Author: Namrata Chhabra

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Low Glutathione reductase activity

Q- A 45-year-old female presents to her primary care doctor with fatigue and tingling/numbness in her extremities (bilateral). Examination reveals a beefy red and fissured tongue. Further evaluation reveals a low Glutathione reductase activity in the red blood cells. Which of the following vitamin deficiencies could have caused her symptoms? A.Vitamin C B. Niacin C. Vitamin B2 D. B6-P E. Vitamin B12   The correct option is C- vitamin B2. The patient is most probably suffering from Vitamin B2 deficiency (Riboflavin deficiency). Most prominent effects of vitamin B2 deficiency are seen on the skin, mucosa and eyes. The characteristic symptoms...

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Hydroxyurea in the treatment of Leukemia

Case details A physician evaluates a 32-year-old patient for fatigue. The patient is found to have an elevated white blood cell count and an enlarged spleen. A referral to an oncologist results in a diagnosis of chronic myelogenous leukemia. Treatment with hydroxyurea, a ribonucleotide reductase inhibitor is begun. The normal functioning of this enzyme is to do which of the following? A. Converts xanthine to uric acid B. Converts ribonucleotides to deoxyribonucleotides C. Degrades guanine to xanthine D. Degrades AMP to IMP E. Converts PRPP to phosphoribosylamine   The correct answer is- B- Converts ribonucleotides to deoxyribonucleotides. Either hydroxyurea or...

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A microcytic anemia and elevated iron levels in tissues

An 8-year-old child has been brought to his pediatrician by his parents after they noticed that he felt very fatigued. They also noted that his abdomen seemed to be enlarged. Examination reveals an enlarged spleen. Further history reveals that the child been given vitamins and iron supplements over the last few months. Laboratory tests show a microcytic anemia and elevated iron levels in tissues. Which of the following conditions is most consistent with the findings in this patient? A. Aplastic anemia B. Sickle cell anemia C. Pernicious anemia D. Thalassemia major E. Thalassemia minor The correct answer is E- Thalassemia...

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Phenylalanine – a source of energy and precursor of neurotransmitters

A 27- year-old semi professional tennis player seeks advice from a hospital -based nutritionist concerning his diet supplements. His coach had given him amino acid supplements consisting of phenylalanine and tyrosine. The rationale was that these precursors to several neurotransmitters will “help his brain focus” on his game. In reality, the excess amino acids are used for energy, with a poor and eclectic diet. Phenylalanine upon metabolism, enter TCA cycle as which of the following? A) Oxaloacetate B) Citrate C) Succinyl Co A D) Fumarate E) α- Ketoglutarate The correct answer is- Fumarate. Phenylalanine is both glucogenic as well as...

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Effect of Lead poisoning on heme biosynthetic pathway

A 3-year- old boy is brought to the emergency room with abdominal pain, mental status changes and fatigue. On taking history the physician finds the child belongs to a very poor family and lives in an old house and has the habit of licking the paint chips that have crumbled in the window sills. The physician suspects lead poisoning. Lead typically interferes with which of the following enzymes? A) Porphobilinogen deaminase B) Protoporphyrinogen oxidase C) ALA synthase D) Coproporphyrinogen oxidase E) ALAdehydratase The correct option is- ALA dehydratase. All the enzymes mentioned above are related with the pathway of heme biosynthesis. Heme is...

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Enzyme that would exhibit Michaelis–Menten kinetics

During an extended period of exercise, the enzymes involved in the glycolytic pathway in muscle tissue are actively breaking down glucose to provide the muscle energy. The liver, to maintain blood glucose levels, is synthesizing glucose via the gluconeogenic pathway. Which of the following enzymes involved in these pathways would be most likely to exhibit Michaelis–Menten kinetics, that is, have a hyperbolic curve when plotting substrate concentration versus velocity of the reaction? A) Fructose-1, 6-bisphosphatase B) Hexokinase C) Lactate dehydrogenase D) Phosphofructokinase-1 E) Pyruvate kinase The correct option is C- Lactate dehydrogenase. All the above mentioned enzymes are allosteric except...

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Starvation induced metabolic alterations

A 23 –year- old female was brought for consultation by her mother who was troubled by her daughter’s continuous fatigue, dizziness and loss of weight. The patient was 6 feet 2 inches tall and weighed 100 pounds. Further questioning revealed that the young woman had been virtually fasting for 4 months hoping to obtain a ‘skinny figure’ as a prelude to a career in modeling. Physical examination revealed dehydration and a fruity odor in her breath. Laboratory results revealed – Blood glucose 50 mg%. Which substance would most likely be detected in abnormally high concentration upon patient’s urine test? A)...

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Carbohydrates induced obesity

An 18-year-old female is diagnosed as obese. She maintains a sedentary life style and eats a high-fat, high-sugar diet. Maintenance of this diet and lifestyle has led to lipogenesis and obesity. Which of the following best explains carbohydrates induced obesity? A) Excess glycerol is obtained through glycolysis B) Fatty acids are excessively synthesized from Acetyl co A C) NADPH is excessively obtained through HMP pathway D) Triglycerides are excessively synthesized E) All of the above. The correct answer is E- All of the above. Excess carbohydrate ingestion is a major cause of obesity. Obesity is a state of excess adipose...

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Role of Thiamine in HMP pathway

Case details A 50 -year-old alcoholic male presents with pain, numbness, tingling and weakness in his feet. He is diagnosed with thiamine deficiency. Thiamine and ATP condense together to form   thiamine pyrophosphate, a cofactor important for the enzymes that catalyze oxidative decarboxylation of (α-keto acids) in the TCA cycle and also at one of the steps in pentose phosphate pathway, which out of the following enzymes requires TPP as a coenzyme ? A) Glucose-6-P dehydrogenase B) Transaldolase C) Transketolase D) 6-P-Gluconate dehydrogenase E) Gluconolactone hydrolase The correct answer is- C) – Transketolase. Two reactions are catalyzed by Transketolase in HMP...

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Implications of suppressed TCA cycle in Diabetes Mellitus

A 22- year-old diabetic comes to the Accident and Emergency department. She gives a 2-day history of vomiting and abdominal pain. She is drowsy and her breathing is deep and rapid. There is distinctive smell from her breath. She has been diagnosed with Diabetic ketoacidosis. Diabetic ketoacidosis is a complication of uncontrolled diabetes mellitus. The TCA cycle in diabetes mellitus is suppressed and the excess Acetyl co A, resulting from fatty acid oxidation is channeled towards the pathway of ketogenesis. Which of the following intermediates of TCA cycle is depleted in Type 1 Diabetes mellitus to suppress TCA cycle? A)...

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Glycerol kinase deficiency in adipose tissue

A 50-year-old, alcoholic male presents with a swollen face, distended abdomen, and an enlarged fatty liver. Fatty acids react with glycerol-3-P to form triglycerides, which accumulate to cause fatty liver. The liver has glycerol kinase, while adipose tissue lacks glycerol kinase. As a result, in adipose tissue, which of the following occurs? A) Glucose cannot be converted to DHAP (dihydroxyacetone phosphate) B) Glycerol cannot be converted to Glycerol-3-P C) DHAP cannot be converted to Glycerol-3-P D) Diacylglycerol cannot be converted to Triacylglycerol E) Triacylglycerols cannot be stored. The correct answer is- B) – Glycerol cannot be converted to Glycerol-3-P. Glycerol...

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Hypoglycemia due to Biotin deficiency?

A 32-year-old body builder has decided to go on a diet consisting of egg whites to ensure only proteins for muscle growth. After a few weeks he experiences decreased energy and is found to be hypoglycemic. A nutritionist tells the patient that he most likely has the deficiency of vitamin Biotin. Which of the following enzymes is unable to catalyze its step in synthesizing glucose from pyruvate? A) Pyruvate carboxylase B) Phospho enol pyruvate carboxy kinase C) Glucose-6-phosphatase D) Fructose 1, 6 bisphosphatase E) Phosphoglycerate kinase. The correct answer is- A) – Pyruvate carboxylase. Biotin deficiency is very common in...

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Case study- Glycosuria

A young infant, who was nourished with a synthetic formula, had a sugar in the blood and urine. This compound gave a positive reducing sugar test but was negative when measured with glucose oxidase (specific test for detection or estimation of Glucose). Treatment of blood and urine with acid (which cleaves glycosidic bonds) did not increase the amount of reducing sugar measured. Which of the following compounds is most likely to be present in this infant’s blood and urine? A. Glucose B. Fructose C. Maltose D. Sorbitol E. Lactose The right answer is fructose. Reducing sugars are usually detected by Benedict’s...

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An amino acid that acts as a component of histones and a precursor for Nitric oxide (NO)

The general structure of chromatin has been found to be remarkably similar in the cells of all eukaryotes. The most abundant proteins associated with eukaryotic DNA (somewhat more than half its mass) are histones, a family of basic proteins rich in the positively charged amino acids that interact with the negatively charged phosphate groups in DNA. Which of the following amino acids acts as a component of histones and a precursor for Nitric oxide (NO)? A. Arginine B. Histidine C. Lysine D. Asparagine E. Leucine The correct answer is- A- Arginine. Histones are nucleoproteins, rich in basic amino acids such...

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Components of Sucrose

A 7-month-old baby girl, the second child born to unrelated parents was brought to Pediatrics outdoor department. History revealed that she did not respond well to breast-feeding and was changed entirely to a formula based on cow’s milk at 4 weeks. Between 7 and 12 weeks of age, she was admitted to the hospital twice with a history of screaming after feeding, but was discharged after observation without a specific diagnosis. Elimination of cow’s milk from her diet did not relieve her symptoms; her mother reported that the screaming bouts were worse after the child drank juice and that she...

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Case details- VNTR Analysis

A 16-year-old girl was abducted when she went to a local store. Her body was found the next morning and the autopsy revealed that she had been sexually assaulted and strangled. Crime scene investigators were able to collect a semen sample from vaginal fluid as well as tissue samples from underneath the victim’s fingernails. DNA samples were obtained from three suspects besides the victim. A variable number of tandem repeats (VNTR) analysis was performed on the DNA samples from the evidence collected, the victim, and the suspect and the results were compared. Which of the following techniques is the most...

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Osazone test

This test is used for the identification of sugars. It involves the reaction of monosaccharide with phenyl hydrazine, a crystalline compound. All reducing sugars form osazones with excess of phenyl hydrazine when kept at boiling temperature. Each sugar has a characteristic crystal form of osazones. Which “one” of the following shapes corresponds with the shape of sucrosazone crystals? A. Needle shaped B. Petal shaped C. Rhombic plates D. Powder puff shaped E. None of the above. Details The correct answer is E- Sucrose is a non reducing sugar, it does not form osazone crystals. Upon hydrolysis, the products glucose and...

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Cloning

A clone is a population of identical organisms derived from a single parental organism. In Molecular biology- A clone is a collection of molecules or cells, all identical to an original molecule or cell. If the original cells harbored a recombinant DNA molecule in the form of a plasmid, the plasmids within the millions of cells in a bacterial colony represent a clone of original DNA molecules; these molecules can be isolated and studied. The mechanism of cloning involves , i) Cutting DNA at precise locations, ii) Joining two DNA fragments covalently, iii) Selection of a small molecule of DNA...

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DNA Repair

The fidelity of replication is very high, with an overall error rate of 10-9 to 10-10. Insertion of an inappropriate nucleotide that occurs during replication can be corrected by editing during the replication process. This proof reading function is performed by a 3′-5′ exonuclease activity associated with the polymerase complex. The post replication repair process also increases the fidelity of replication. Which “one” of the following is not a post replication DNA repair mechanism? A. 5′-3′ – Exonuclease repair B. Base excision repair C. Mismatch repair D. Nucleotide excision repair E. Direct repair The answer is- A – 5′-3′ – Exonuclease repair....

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Frameshift mutations

Duchenne muscular dystrophy (DMD) is an X-linked disorder due to a frameshift mutation in the muscle protein “Dystrophin”. The patients have proximal muscle weakness and muscle fibrosis, with death occurring as a result of cardiac or respiratory failure. Which ‘one’ of the following statements correctly describes a frameshift mutation? A. The frameshift mutations occur due to substitution of the base analogs B. The reading frame beyond the mutation remains unaltered C. A frameshift mutation may not produce effects due to degeneracy of the genetic code D. Insertion or deletion of three nucleotides does not alter the reading frame beyond the...

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Splicing

The most common cause of β- Thalassemia is the defect in mRNA splicing of the beta globin gene. Mutations that affect the splicing create aberrant transcripts that are degraded before they are translated. If patients inherit a single mutated gene (thalassemia minor), the disease manifests with a mild anemia. However, patients with homozygous mutations (thalassemia major) have severe transfusion-dependent anemia. Which of the following types of RNA are involved in the splicing process? A. Ribosomal RNA (r RNA) B. Small nuclear RNA (sn RNA) C. Transfer RNA (t RNA) D. Small cytoplasmic RNA (sc RNA) E. Heterogeneous nuclear RNA (hn...

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Restriction enzymes and DNA fingerprinting

DNA fingerprinting is used in the legal world to determine parentage, genealogy, or other genetic relationships, or to implicate suspects in law enforcement investigations involving violent crimes. Fragments produced by various restriction enzymes from a number of different loci can be used to identify individuals with the accuracy of a fingerprint. Therefore, this technique is called “Fingerprinting”. Which “one” of the following statements is incorrect about restriction enzymes? A. They are site specific endonucleases B.  The restriction sites are palindrome in nature C. All restriction enzymes are of bacterial origin D. They always produce complementary single stranded overhangs E. They...

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Histidine to histamine conversion

Histamine causes vasodilatation and bronchoconstriction. In the stomach it stimulates the secretion of hydrochloric acid (HCl). Histamine binds to H1 receptors in the stomach, stimulating the release of gastric acid. Pharmacological blockers of H1 receptors are used in the treatment of gastric reflux. H2 receptors are located on basophils; histamine stimulates their degranulation during the allergic responses. H2 receptor blockers are used to treat allergic conditions. Histamine is produced from Histidine by: A. Deamination B. Transamination C. Carboxylation D. Decarboxylation E. Methylation The correct answer is D- Decarboxylation. Histamine is a biogenic amine. A biogenic amine is a potent signaling...

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Cholesterol transport and Tangier disease

Tangier disease is a disease of cholesterol transport. The first case was identified in a patient who lived on the island of Tangier and who had characteristic orange-colored tonsils, a very low HDL level, and an enlarged liver and spleen. Due to a mutation in the transport protein the cholesterol cannot properly exit the cell to bind to apo A (that forms HDL). This results in a very low HDL levels. Cholesterol obtained by HDL from cell membranes is converted to cholesterol esters. Which of the following enzymes catalyzes the esterification of cholesterol? A. HMG Co A reductase B. Lecithin:...

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Lactate to glucose conversion

Lactate is oxidized to pyruvate in a reaction catalyzed by Lactate dehydrogenase. The patients with genetic deficiency of lactate dehydrogenase present with muscle cramping and myoglobinuria after intense exercise. The sources of lactate include muscle and red blood cells. Lactate is a waste product in such cells; it is transported to liver and can be converted to glucose through pathway of gluconeogenesis. The energy requirements for conversion of lactate to glucose are: A. 2 ATP B. 4 ATP C. 6 ATP D. 8 ATP E. 38 ATP. The correct answer is C- 6 ATP. Lactate produced by active skeletal muscle...

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Energy output per Acetyl co A by one round of TCA cycle

The total energy generated by one round of TCA cycle starting with 1 Acetyl co A is approximately 12 ATP. Of this total energy output, what percentage is contributed by oxidation of niacin dependent coenzymes in the electron transport chain? A. 38% B. 42% C. 86% D.75 % E. 100% The correct answer is D- 75%. The citric acid cycle (Krebs cycle, tricarboxylic acid cycle) includes a series of oxidation-reduction reactions in mitochondria that result in the oxidation of an acetyl group to two molecules of carbon dioxide and reduce the coenzymes that are reoxidized through the electron transport chain,...

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Pitocin – a synthetic form of Oxytocin

Pitocin is a synthetic form of Oxytocin that can be administered during labor to initiate uterine contractions or augment labor in the event of the failure of the normal progression of labor. Chemically Oxytocin is a: A. Glycoprotein B. Glycolipid C. Peptide D. Nucleoprotein E. Lipoprotein. The correct answer is C- Peptide Peptides are short polymers of amino acids. Physiologically they perform prominent roles  in the neuroendocrine system as hormones, hormone-releasing factors, neuromodulators, or neurotransmitters. Clinically some of the peptides are used as antibiotics, anticancer drugs and some in toxic dosage promote tumor formation. Summary of biologically important peptides (Alphabetically)...

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Free radical injury and antioxidants

The organic solvent Carbon tetra chloride (CCl4) is used in the dry cleaning industry. The Carbon tetra chloride (CCl4) is metabolized in the body by cytochrome P450 enzyme system to form a free radical species CCl3– . This highly reactive species causes a chain reaction of lipid peroxidation, particularly in the liver, that can lead to hepatocellular necrosis. The cells have developed enzymes and other molecules to help them protect against the free radical damage. Some dietary components also act as anti-oxidants. Which of the following dietary components can provide some protection against free radical injury? A. Glutamine B. Linoleic...

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Glucose transporter-1(GLUT-1)

Glucose travels across the cell membrane on a transport protein. Hereditary deficiency of GLUT-1, insulin -independent transporter, results in decreased glucose transport. Patients manifest with intractable seizures in infancy and a developmental delay. GLUT-1 transporter is expressed in which of the following cell types? A. Liver, kidney and pancreatic β cells B. Brain (neurons) C. Adipose tissue, skeletal muscle and cardiac muscle D. Erythrocytes, Blood -brain barrier, blood-retinal barrier E. Intestinal epithelium, Spermatozoa. The correct answer is- D, Erythrocytes, Blood -brain barrier, blood-retinal barrier. Basic concept Glucose transport across the cell membrane is a facilitated transport, a carrier mediated transport....

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Reaction catalyzed by Xanthine oxidase

Allopurinol, (the inhibitor of xanthine oxidase), is used in the treatment of Gout. More recently, febuxostat, a novel nonpurine analog inhibitor of xanthine oxidase, has been used. Which of the following reactions is catalyzed by xanthine oxidase? A. Hypoxanthine to Xanthine B. Xanthine to Hypoxanthine C. Hypoxanthine to uric acid D. Inosine to hypoxanthine E. Adenosine to Inosine. The correct answer is- A, Conversion of hypoxanthine to xanthine. Basic concept Gout is a metabolic disease most often affecting middle-aged to elderly men and postmenopausal women. It is the result of an increased body pool of urate with hyperuricemia, typically characterized...

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Significance of Glycine

Glycine functions as an inhibitory neurotransmitter in the brain stem and the spinal cord. Its actions are antagonized by the rodenticide Strychnine, leading to twitching and muscle spasm. The non availability of glycine can affect the synthesis of which of the following compounds? A. Methionine B. Hippuric acid C. Glucuronic acid D. Cysteine E. Mercapturic acid. Details The correct answer is- B- Hippuric acid Aromatic compounds like benzoic acid obtained from diet are detoxified by conjugation with glycine to form Hippuric acid (figure-1) which is excreted in urine.  This reaction takes place exclusively in liver. Hippuric acid excretion test is...

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Cholesterol content and membrane fluidity

Membrane fluidity is required for the proper movement of erythrocytes through capillaries of the spleen. Patients with spur cell anemia have increased cholesterol content (> 40%) in the membranes of their erythrocytes, resulting in decreased membrane fluidity. Thus, erythrocytes from these patients are destroyed in the spleen. Which of the following statements is incorrect concerning the significance of cholesterol? A. Elevated levels of cholesterol are associated with atherosclerosis. B. The serum total cholesterol content should be less than 200 mg/dl. C. Cholesterol is a major component of gall stones. D. Excess cholesterol is excreted from the liver in the bile...

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Effect of pH on enzyme activity

The optimal pH for pepsin is 2, reflecting its need as a digestive enzyme in the gastric juice of the stomach; whereas the optimal pH for alkaline phosphatase is 9, reflecting the basic environment in bone (Figure-1)   Figure-1- Effect of pH on catalytic activity of enzyme. Changes in the pH can alter these changes, so that the reaction proceeds at a slower rate. If the pH is too high or too low, the enzyme can also undergo denaturation. Which of the following statements is true of denaturation? A. The enzyme loses its capacity to hold the substrate B. The...

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Chemical nature of sialic acid- Question of the day.

The influenza virus infects cells by binding its viral hemagglutinin to “Sialic acid” on the surface of epithelial cells. Which of the following represents the true chemical nature of sialic acid? A. Glycolipid B. Amino sugar C. Amino sugar acid D. Lipoprotein E. Glycoprotein. Details The correct answer is C- Amino sugar acid. Sialic acid is a sugar derivative. Basic concept Amino sugars Amino groups may be substituted for hydroxyl group of sugars to give rise to amino sugars. Generally, the amino group is added to the second carbon of the hexoses. The most common amino sugars are Glucosamine and...

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Gray Baby syndrome and the role of Glucuronic acid

Case details Infants have decreased ability to conjugate Glucuronic acid on to drugs such as Chloramphenicol. Administration of this antibiotic during the neonatal period can result in elevated plasma levels of the drug and a fetal shock-like syndrome referred to as Gray Baby syndrome. Glucuronic acid is produced from Glucose in the Uronic acid pathway by the process of: A. Oxidation B. Reduction C. Hydrolysis D. Carboxylation E. Decarboxylation. Details The correct answer is- A- Oxidation. Glucuronic acid is produced from Glucose by oxidation in the Uronic acid pathway, which is an alternative pathway of glucose utilization. Glucuronic acid in...

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ATP- The energy currency within the cell

Q.- Adenosine triphosphate (ATP) is the energy currency within the cell. Which of the following best describes the type of compound ATP is? A. Phospholipid B. Amino acid C. Nucleotide D. Triacylglycerol E. Oligosaccharide.  Details The correct answer is -C- Nucleotide. The nucleotide coenzyme adenosine triphosphate (ATP) is the most important form of chemical energy in all cells.  All fuel sources of nature, all foodstuffs of living things, produce ATP, which in turn powers virtually every activity of the cell and organism. Cleavage of ATP is strongly exergonic. The energy provided is used to drive endergonic processes (such as biosynthesis and...

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Characteristics of Phospholipids

Q.1- Which one of the following characteristics of phospholipids is correct? A. They always contain choline and glycerol B. They are important source of energy during fasting C. They are major components of membranes D. They are uncharged at physiological pH E. They are water insoluble. Details The correct answer is -C, they are major components of membranes. The phospholipids are compound lipids. They contain in addition to fatty acids and glycerol/or other alcohol, a phosphoric acid residue, nitrogen containing base and other substituents. Phospholipids may be regarded as derivatives of phosphatidic acid , in which the phosphate is esterified...

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Aromatase inhibitor acting by increasing km value

Case details An 8-year-old girl presents with precocious puberty, short stature, and coffee-colored macules. The patient has been diagnosed with McCune-Albright syndrome that results from estrogen production due to excessive Aromatase activity from ovarian follicular cysts. To treat the precocious puberty and other symptoms, the patient has been prescribed with a drug that inhibits the Aromatase activity. The drug is known to act by binding to substrate binding site, producing an increase in km. Which of the following choices best describes the mechanism of inhibition of the drug? A. Competitive B. Non Competitive C. Allosteric D. Suicidal E. Feedback inhibition...

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Question of the day-Enzyme catalyzing Carbon-Carbon bond cleavage in Glycolysis

Which of the following enzymes cleaves a carbon-carbon bond in glycolysis? A. Phospho triose isomerase B. Aldolase C. Phospho glycerate kinase D. Enolase E. Pyruvate Kinase The correct answer is B- Aldolase. The Aldolase cleaves fructose-1,6-bisphosphate (the product of 2nd glycolytic reaction catalyzed by Phospho fructo kinase -1) between the C-3 and C-4 carbons to yield two triose phosphates. The products are dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (figure). Figure- Reactions of glycolysis. Phospho triose isomerase Of the two products of the Aldolase reaction, only glyceraldehyde-3-phosphate goes directly into the second phase of glycolysis. The other triose phosphate, dihydroxyacetone phosphate, must be...

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Role of “Nucleoside analogs” in HIV infection

Case details A 34-year-old homosexual man has recently been diagnosed with HIV (human immunodeficiency virus) infection. His CD4+ T-cell count has dramatically decreased, and he has a high viral load. He has been referred to an infectious disease clinic where he has been prescribed with a nucleoside analog. The nucleoside analogs inhibit DNA synthesis. Which of the following chemical groups essentially required for DNA polymerization is absent in the nucleoside analogs? A. 5′ Phosphate B. 3′ Hydroxyl C. 2′ Methyl D. 3′-Phosphate E. 5′ Hydroxyl. The correct answer is- B-3′ Hydroxyl. Basic concept Nucleosides Nucleosides are derivatives of purines and pyrimidines...

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Prokaryotes versus Eukaryotes

Case details A young man was brought to the emergency room after being hit by a car. His leg bone was broken in half, and the bone was protruding through the skin. He was recovering well after the orthopedic surgery. After several days he developed wound infection. The wound culture revealed a new bacterial organism that was resistant to all available antibiotics. The drugs acting as antibiotics specifically inhibit bacterial proliferation by inhibiting any of the processes such as replication, transcription or translation. Which of the following statements is exclusively true of prokaryotes but not of eukaryotes? A. Most of...

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Nonessential in normal health but essential during conditions of enhanced growth or surgical recovery

Case details An 8-year-old child requires surgical intervention and substantial recovery time in the hospital. A nutritionist recommends a specific dietary plan. The plan includes a protein rich diet with the special supplementation of an amino acid that is typically considered a nonessential, but becomes an essential amino acid under conditions of enhanced growth or surgical recovery. Which of the following amino acids should be considered in this dietary plan? A. Alanine B. Arginine C. Glycine D. Serine E. Tyrosine The correct answer is Arginine. Arginine is a semi essential amino acid. It can be synthesized in the human body...

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Elevated Acylcarnitine compounds and associated hypoglycemia- What is the defect?

Case details A 5- year-old boy suffered gastroenteritis for two days and was brought to emergency in the semiconscious state. Blood glucose at the time of admission was 45 mg/dl and his urine was negative for glucose and ketone bodies. Glucose was administered intravenously and his condition improved within 10 minutes. Subsequent laboratory investigations revealed elevated acylcarnitine residues. The child was diagnosed with an enzyme deficiency. The parents were instructed to feed the child more frequently. Which of the following enzymes might be deficient? A. Acyl Co A synthetase B. Carnitine Acyl transferase-1 C. Translocase D. Carnitine Acyl transferase-2 E....

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Diabetic ketoacidosis- Enzyme for ketones formation?

Case details A 54- year-old man with Type 1 diabetes is referred to an ophthalmologist for evaluation of developing cataract. Blood chemistry results are shown below- Fasting blood glucose   198 mg/dl Hemoglobin A                  15 gm/dl Hemoglobin A 1c             10% of total Hb Urine ketones                   Positive Urine glucose                    Positive Which of the following enzymes is most strongly associated with ketones formation in this patient? A) Pyruvate dehydrogenase complex B) Thioesterase C) Thiophorase D) Thiokinase E) Thiolase. The correct answer is- E- Thiolase. Out of the given options thiolase is the only enzyme involved in the ketogenesis. The process of ketogenesis starts from...

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Case study- Glycogen storage disease

Case details A female infant appeared normal at birth but developed signs of liver disease and muscular weakness at 3 months. She had periods of hypoglycemia, particularly on awakening. Examination revealed an enlarged liver. Laboratory analyses following fasting revealed ketoacidosis, blood pH 7.25, and elevations in both alanine transaminase (ALT) and aspartate transaminase (AST). Administration of glucagon following a carbohydrate meal elicited a normal rise in blood glucose, but glucose levels did not rise when glucagon was administered following an overnight fast. Liver biopsy revealed an increase in the glycogen content (6 percent of wet weight). In which of the...

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Mechanism of action of Rifampin?

Case details A 37-year-old, female develops fever, night sweat, weight loss, and a blood- tinged cough. While in the emergency room, an infectious disease specialist is consulted, she is suspected to have pulmonary tuberculosis and is immediately prescribed with a multidrug regimen that includes rifampin (Figure). Rifampin inhibits RNA transcription because it inhibits the enzyme- A) DNA- dependent DNA polymerase B) DNA- dependent RNA polymerase C) RNA- dependent DNA polymerase D) RNA- dependent RNA polymerase E) Reverse transcriptase. Figure- Rifampin is widely used as an antitubercular drug. The correct answer is- B) DNA dependent RNA polymerase. DNA-dependent RNA polymerase is...

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RNA splicing

Case details A 45-year- old female of Indian origin reported for a routine checkup. She had no complaints and was in good health; however she reported a family history of anemia. Her complete blood count demonstrated mild anemia and the attending physician suspected thalassemia minor in the patient. Thalassemia is most often due to a defect in RNA splicing, which is best explained by which of the following statements? A) A high molecular weight precursor is trimmed to a short and mature m RNA. B) The coding regions found on the introns are rearranged and joined together. C) The introns...

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Excessive Nasogastric (NG) drainage and acid base status

Case details A postoperative surgical patient had a nasogastric tube (figure) in for three days.   Figure- Nasogastric tube   The nurse caring for the patient stated that there was much drainage from the tube that is why she felt so sick. What could be the reason? A. Metabolic Acidosis B. Metabolic Alkalosis C. Respiratory Acidosis D. Respiratory Alkalosis E. None of the above. The correct answer is- B-Metabolic alkalosis. Metabolic alkalosis is primary increase in HCO3 − with or without compensatory increase in PCO2; pH may be high or nearly normal. Whenever a hydrogen ion is excreted, a bicarbonate ion is gained into the extracellular...

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Breathing difficulty- What is the acid- base imbalance?

Case details An 80-year-old man had a bad cold. After two weeks he said, “It went in to my chest; I am feeling tightness in my chest, I am coughing, suffocated and unable to breathe!” (Figure) Figure- The gaseous exchange is impaired in pulmonary diseases What could be the possible reason? A. Metabolic Acidosis B. Metabolic Alkalosis C. Respiratory Acidosis D. Respiratory Alkalosis E. None of the above. Answer- C- Respiratory acidosis is the correct answer. Respiratory acidosis is CO2 accumulation (hypercapnia) from a decrease in respiratory rate, respiratory volume (hypoventilation), or both. It can be due to severe pulmonary...

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Vitamin deficiency in cystic fibrosis

Case details A 30-month-old female child whose growth rate has been in the lower 10th percentile over the last year presents with chronic, nonproductive cough and diarrhea with foul-smelling stools. She is diagnosed as having cystic fibrosis (figure-1). For which of the following vitamins is this child most likely to be at risk of deficiency? A. Ascorbic acid (vitamin C) B. Biotin C. Folic acid D. Retinol (vitamin A) E. Riboflavin (vitamin B2) Answer- D. Because cystic fibrosis leads to pancreatic damage and diminution of the ability to secrete HCO3 ions and pancreatic digestive enzymes with the result that fat...

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Alcohol induced hypoglycemia

Case details A known alcoholic is found lying semiconscious at the bottom of a stairwell with a broken arm by his landlady, who called an ambulance to take him to the emergency room. Initial laboratory studies showed are relatively large anion gap of 34 (normal = 9 to 15). His blood alcohol was elevated at 245 mg/dL (intoxication level = 150 to 300 mg/dL), and his blood glucose was 38 mg/dL (low normal). The patient/s large anion gap and hypoglycemia can best be explained by which of the following? A. Decreased secretion of glucagon B. Increased secretion of insulin C....

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Protein folding defect

Case details A 50-year-old male presents with “dancing –like” movements of his arms and progressive dementia. He cannot control the movement of his arms. He states that he knows that he has Huntington’s disease because his mother has the same disease. The disease is caused by abnormal protein folding. Which of the following helps to mediate proper protein folding? A. Chaperones B. Transcription factors C. DNA binding proteins D. RNA binding proteins E. All of the above.   Figure-Folding of a protein to acquire a mature functional conformation Discussion- The correct answer is Chaperones. Most proteins must fold into defined three-dimensional...

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Implications of maternal hyperglycemia

Case details A pregnant mother with a history of long-standing uncontrolled diabetes mellitus has come for a routine check up. The examination reveals a normal pregnancy. Blood chemistry reveals random blood glucose – 165 mg/dl and Glycated hemoglobin (HbA1c) of 10.5 %. What are the possible complications in a fetus under such conditions of maternal hyperglycemia? A. Fetal hyperglycemia B. Large fetal size C. Hypoglycemia after birth D. Fetal hyperinsulinemia E. All of the above. See the image below and try to find out the answer Figure- Showing the implications of maternal hyperglycemia. The correct answer – E- all of the...

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Role of ACAT in the esterification of cholesterol

See the image below and note the role of ACAT (Acyl Co A cholesterol acyl transferase) in the esterification of cholesterol. Cholesterol is stored in the cell in the form of cholesteryl esters. Esterification involves the coupling of cholesterol with a fatty acid, generally this fatty acid is a- A. Saturated fatty acid B. Monounsaturated fatty acid C. Polyunsaturated fatty acid D. Dienoic acid E. Any of the above. Figure-1- Uptake of LDL and fate of cholesterol The correct answer is- Monounsaturated fatty acid, Commonly Oleic acid is used for the esterification (figure-2) Oleic acid is a mono- unsaturated fatty...

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The role of Phytosterols in reducing the risk of heart disease

A 65-year-old man has been taking low-dose aspirin to reduce his risk of heart disease. He adds phytosterols to his daily regime for which of the following? A. To reduce circulating triglyceride levels B. To reduce circulating cholesterol levels C. To reduce endogenous cholesterol synthesis D. To decrease insulin secretion E. To reduce fatty acid biosynthesis The answer is B: To reduce circulating cholesterol levels. Phytosterols interfere with cholesterol absorption in the intestine (through blockage of cholesterol incorporation into the mixed micelles, which are necessary for intestinal epithelial cells to absorb dietary cholesterol), (figure-1), thereby leading to a reduction in...

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Case study- Hyperammonemia

Question of the day -Hyperammonemia A new-born becomes progressively lethargic after feeding. His respiratory rate increases and he becomes virtually comatose, responding only to painful stimuli, and exhibits mild respiratory alkalosis. Suspicion of a urea cycle disorder is aroused and evaluation of serum amino acid levels is initiated. In the presence of hyperammonemia, production of which of the following amino acids is always increased? A. Glycine B. Arginine C. Proline D. Histidine E. Glutamine Answer- The correct answer is Glutamine. Urea cycle disorder results in reduced ammonia disposal and hence the patients present with symptoms of hyperammonemia. Ammonia is detoxified by...

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A common intermediate of Urea and TCA cycle

Question of the day Which one of the following can be converted to an intermediate of either the citric acid cycle or urea cycle? A. Tyrosine B. Lysine C. Leucine D. Tryptophan E. Aspartate Answer- The correct answer is- E -Aspartate. 1) Role of Aspartate in urea cycle Aspartate participates in urea cycle for condensation with citrulline to form Argino succinic acid. The reaction is catalyzed by Argino succinic acid synthetase (Aspartate provides one out of the two nitrogens of urea, the other nitrogen is contributed by Glutamate). In the subsequent reaction, Argino succinic acid undergoes a lytic reaction to...

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Immediate treatment of Acute MI

Case details A 56-year-old man with hypercholesterolemia was rushed to the hospital with crushing chest pain radiating to his left arm and a probable heart attack. Which of the following treatments should be considered? A. A platelet transfusion B. Heparin transfusion C. Thrombin transfusion D. Fibrinogen infusion E. Tissue plasminogen activator infusion The correct answer is- E- Tissue plasminogen activator infusion. Tissue plasminogen activator (tPA) causes activation of plasminogen (zymogen form) to plasmin (active form). Plasmin hydrolyzes fibrin to form soluble degradation products (Figure-1). Figure-1- Mechanism of action of tPA The main goals of medical therapy of acute myocardial infarction...

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Action of Alpha- Amylase on starch

Prior to a race, many marathon runners will try to increase their glycogen concentrations by loading up with foods with high starch content, such as pasta. α-Amylase secreted by the pancreas will digest the starch into which of the following major products? A. Amylose, amylopectin, and maltose B. Glucose, galactose, and fructose C. Glucose, sucrose, and maltotriose D. Limit dextrins, maltose, and maltotriose E. Limit dextrins, lactose, and sucrose   Answer- The correct answer is-D- Limit dextrins, maltose, and maltotriose Starch consists of two fractions. About 20% is a water soluble material called Amylose. The majority of the starch is...

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Angular stomatitis and impaired TCA cycle activity

Case details A postoperative patient on intravenous fluids develops lesions in the mouth (angular stomatitis). Urinalysis indicates an excretion of 15 μg riboflavin/mg creatinine, which is abnormally low. Which of the following TCA cycle enzymes is most likely to be affected? A. Citrate synthase B. Isocitrate dehydrogenase C. Fumarase D. Malate dehydrogenase E. Succinate dehydrogenase Answer- The correct answer is- E- Succinate dehydrogenase Angular stomatitis and low excretion of riboflavin are indicators of underlying Riboflavin deficiency, hence the activities of only Riboflavin requiring enzymes would be affected . Riboflavin functions in several different enzyme systems. Two derivatives, riboflavin 5′ phosphate (flavin...

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Which amino acid is both glucogenic as well as ketogenic ?

A 54-year-old male who was diagnosed with HIV (human immuno deficiency virus) infection 2 years back, is currently in the terminal stage. He is now cachectic and having a difficult time obtaining any caloric intake yet he refuses to take a naso gastric or gastric feeding tube. Since his muscle and organs are metabolically active, which of the following amino acids will produce both glucose and ketone bodies as an energy source? A. Alanine B. Tyrosine C. Proline D. Glycine E. Leucine The correct answer is B- Tyrosine. Amino acids can be classified based on their metabolic fate- I) Purely...

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Role of dietary fiber

A 65-year-old man expresses his concern about developing colon cancer to his physician. He states that his father as well as grandmother died of colon cancer. After performing a physical exam and observing unremarkable colonoscopy, the physician recommends a diet low in fat and high in fiber. The physician explains that studies have shown a decreased risk of colon cancer with insoluble fiber consumption. Which of the following bonds is responsible for the fiber’s inability to be digested? A. α (1->4) B. α (1->6) C. β (1->4) D. β (1->6) E. α (1->2) Answer- The correct answer is – C-...

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Low body fat mass and hormone levels ?

An 11-year-old girl is presented at the clinic with reports of frequent fainting and lethargy. The girl is 5 ft tall and weighs 80 lb. Skin fold tests show an abnormally low percentage of body fat mass. Which of the following hormones is likely to be severely diminished in this patient? A. Cortisol B. Epinephrine C. Glucagon D. Insulin E. Thyroid Answer- The correct answer is D. The patient has low body weight and fat mass and there are frequent fainting attacks. Apparently her condition is consistent with a low energy state that might be due to poor diet or...

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Galactosemia and impaired interconversions ?

A newborn infant presents with poor feeding, vomiting, jaundice and an enlarged liver. The urine test is positive for a reducing substance. Which of the following conversions is most likely to be normal? A. Glucose to Galactose B. Activated galactose to activated Glucose C. Lactose to galactose D. Excretion of galactose by kidney E. Excretion of glucose by kidney Answer- The correct answer is- B- Conversion of activated galactose to activate glucose. As evident from the clinical features, the child is suffering from Galactosemia. Galactosemia is associated with the following 3 enzyme deficiencies; 1) Classical galactosemia is a major symptom...

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Nitrogen balance

A 22 -year-old man started to work out twice a day with the goal of competing in an upcoming bodybuilding competition. Despite his strict working routine, he continues eating a diet of fast food hamburgers and French fries. After a gain of 15 pounds, it is likely he is in a: A. Vitamin overload B. Negative nitrogen balance C. Positive nitrogen balance D. State of decreased BMR E. State of increased BMR Answer- The correct answer is- C-Positive nitrogen balance. The gain in weight despite strict work out signifies positive nitrogen balance. The state of protein nutrition can be determined...

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Question of the day- Energy required for conversion of glycerol to glucose?

A 45-year-old obese male presents for a routine examination. He has a sedentary life style and eats a high-fat diet. His triglyceride level is abnormally elevated. When glycerol derived from adipose triglycerides is converted to glucose, how many moles of high- energy phosphates are required? A. 1 B. 2 C. 3 D. 4 E. 6 Answer- The correct answer is B- 2 ATP. Glycerol is phosphorylated at the expense of ATP to form Glycerol-3-P; the reaction is catalyzed by glycerol Kinase. Glycerol-3-P enters the main pathway of Gluconeogenesis at the level of Dihydroxy acetone-P (Figure-1). Since glycerol is a three...

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Mechanism of action of Insulin ?

Case details A 16-year-old type 1 diabetic female checks her finger stick blood glucose before a meal. She injects herself subcutaneously with exogenous insulin and then starts to eat. As Insulin is absorbed in to her blood, it binds to insulin receptors that activate: A. Tyrosine kinase B. Adenylate cyclase C. Cyclic AMP D. Protein kinase C E. Phospholipase C The correct answer is- A- Tyrosine kinase. Insulin binding to its receptor stimulates intrinsic tyrosine kinase activity (figure -1) leading to receptor auto phosphorylation and the recruitment of intracellular signaling molecules, such as insulin receptor substrates (IRS). IRS and other...

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Source of glycerol-3-P in adipose tissue?

Glycerol produced from hydrolysis of triglycerides in adipose tissue is a waste product, since it has to be in glycerol-3-P form and the enzyme for phosphorylation, glycerol kinase is absent in the adipose tissue. Glycerol -3-P can still be produced in the adipose tissue through interconversion of one of the glycolytic intermediates. Which of the following glycolytic intermediates can be used for the synthesis of glycerol-3-P? A. Phosphoenol pyruvate B. 1, 3 Bisphosphoglycerate C. Dihydroxyacetone phosphate D. Fructose 1, 6 bisphosphate E. 2-Phosphoglycerate The correct answer is C- Dihydroxy acetone phosphate. In adipose tissue glycerol-3-p is obtained through glycolysis from...

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Prolonged fasting and gluconeogenesis…

A 14-year-old high school girl who is extremely conscious about her appearance has gone a full day fasting to fit in to a dress she intentionally brought a size smaller than her actual size for a dance party. Which of the following organs/tissues contribute to the glucose that is being synthesized through gluconeogenesis during periods of prolonged fasting? A. Spleen B. Red blood cells C. Skeletal muscle D. Liver E. Brain D-Liver is the correct answer. Gluconeogenesis is the process of converting noncarbohydrate precursors to glucose or glycogen. The major substrates are the glucogenic amino acids, lactate, glycerol, and propionate....

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Milky plasma- Your diagnosis ??

A teenage boy presents with moderate to severe epigastric pain. Physical examination reveals extensive eruptive xanthomas and hepatosplenomegaly. A blood sample reveals milky plasma. Which of the following is the most likely lipoprotein to be elevated in this patient’s plasma? A. Chylomicrons B. Chylomicron remnants C. HDL D. IDL E. LDL The correct answer is A- Chylomicrons. Clinical features and history are suggestive of Type I Hyperlipidemia (Chylomicronemia) that occurs due to deficiency of Lipoprotein lipase . Familial lipoprotein lipase deficiency is an example of a primary disorder in which a deficiency of lipoprotein lipase in tissue leads to a...

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Role of Insulin in Diabetic ketoacidosis

Case details An 8-year old boy, a known diabetic (type 1 DM), has been brought to emergency room in a state of coma. His breathing is rapid and deep, and his breath has a fruity odor. His blood glucose is 480 mg/dL. The attending physician has administered IV fluids, insulin, and potassium chloride. A rapid effect of insulin in this situation is to stimulate A. Gluconeogenesis in liver B. Fatty acid release from adipose C. Glucose transport in muscle D. Ketone utilization in the brain E. Glycogenolysis in the liver Answer- The right answer is- c) Glucose transport in muscle....

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Significance of Lipoproteins

Case details A 50 -year-old male presents with weakness in his left leg. History reveals that he is a known hypertensive and a diabetic from the past 5 years, but is non- compliant to medication. Based on the clinical findings and imaging of the brain, he has been diagnosed with “Brain stroke”. His serum total cholesterol is abnormally elevated. Which of the following would also be expected to be abnormally high? A. Chylomicrons B. LDL C. HDL D. VLDL E. IDL The correct option is- B, LDL (Low density lipoprotein) Lipids absorbed from the diet and synthesized by the liver...

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# About the web site

Dear viewers, This web site emphasizes on discussion of the essentials of Biochemistry with Clinical correlations. The purpose of this web site is to present a clear discussion of Biochemistry in relation to physiological processes occurring at the cellular levels and to cite examples of deviant biochemical processes in different clinical conditions. A clinical problem is published and the discussion is held subsequently. Through each case study the fundamentals of the basic defect, entire format of pathophysiology and the clinically relevant details are provided. The motive of this web site is not only to inculcate knowledge but also to make...

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Case study- Starvation

Case details A 25 –year-old woman living alone became severely depressed after the termination of her engagement. Two months later, she was brought to the emergency room by a friend because of weakness and lethargy. She appeared thin and pale. Questioning revealed that she had not eaten for several weeks. Analysis of a plasma sample indicated elevated levels of acetoacetate, β hydroxybutyrate, and blood urea nitrogen (BUN). However her plasma glucose concentration was within normal limits. She was hospitalized, given intravenous feeding and antidepressant medications and subsequently shifted to an 1800 Cal (7500 kJ) diet. Her recovery was uneventful. During...

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Case study- Renal glycosuria

Case details A 22-year-old man collapsed from dehydration during maneuvers in the desert and was sent to the emergency. A high level of glucose was observed in his urine. He was suspected of being a diabetic. Further tests, however, determined that his serum insulin level was normal. A glucose tolerance test exhibited a normal pattern; further testing of the urine revealed that only D-glucose was elevated. Other sugars were not elevated. The patient was diagnosed with, ‘Renal glycosuria’. This patient’s elevated urinary glucose and his dehydration episode are caused by a deficiency in which of the following? A. GLUT 2...

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Hyperglycemia induced complications in diabetes mellitus

A 65-year-old man with a history of type 2 diabetes mellitus is complaining of blurred vision and numbness in his toes. Laboratory results are significant for an increased BUN and creatinine, indicative of renal failure and high HbA1c indicative of chronic persistent hyperglycemia. Out of the several mechanisms proposed, one mechanism responsible for hyperglycemia induced complications in diabetes mellitus is non enzymatic attachment of excess glucose with structural proteins by forming covalent bonds. This reaction should be best described as- A. Acylation B. Carboxylation C. Hydroxylation D. Esterification E. Glycation The correct answer is E- Glycation. In diabetes mellitus, insulin...

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Methotrexate in rheumatoid arthritis

Case details A 63- year-old woman presents with a long history of joint pains. Physical examination reveals severely deformed fingers secondary to rheumatoid arthritis. The rheumatologist recommends Methotrexate. This drug inhibits which of the following conversions? A. Dopamine to norepinephrine B. Tyrosine to Dopa C. Folate to dihydrofolate D. Histidine to formiminoglutamate (FIGLU) E. Norepinephrine to Vanillylmandelic acid The correct answer is- C. Folate to dihydrofolate conversion. The reaction is catalyzed by dihydrofolate reductase; the same enzyme catalyzes the conversion of Dihydrofolate to tetrahydrofolate. The enzyme is competitively inhibited by Methotrexate, which is also used as an anticancer drug. It...

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Fructose 2, 6 Bis phosphate and regulation of glycolysis

Case details A patient presents with dizziness, fatigue and tremors. A finger stick test indicates blood glucose of 36mmol/L. Of the allosteric activators of glycolysis in the liver, which of the following is the most important in maintaining a normal blood glucose level? A. Citrate B. ATP C. Fructose 2, 6 bisphosphate D. Glucose-6-Phosphate E. Acetyl Co A The correct answer is- C- Fructose 2,6 bisphosphate Generally, enzymes that catalyze essentially irreversible steps in metabolic pathways are potential sites for regulatory control.  Although most of the reactions of glycolysis are reversible, three are markedly exergonic and must therefore be considered...

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Muscle glycogen synthesis in the resting phase…

A 28- year-old professional cyclist has been training for a race. His coach strongly suggests the intake of carbohydrates after his workout to ensure a muscle glycogen storage that can endure the 28-day race. The activity of muscle Glycogen synthase in the resting muscles is increased by the action of which of the following? A. Epinephrine B. Glucagon C. Insulin D. Cortisol E. Thyroid hormone The correct answer is- C- Insulin. Glucose homeostasis reflects a balance between hepatic glucose production and peripheral glucose uptake and utilization. Insulin is the most important regulator of this metabolic equilibrium, but neural input, metabolic signals,...

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Digoxin- Chemistry and mechanism of action

A 57 -year-old man has been admitted with congestive heart failure. He has been given Digoxin, which helps the heart to beat more strongly and regularly. Digoxin is an ester that contains a sugar component (glycol) and a non sugar (aglycone) component attached via oxygen. Digoxin should be best classified as a: A. Disaccharide B. Glycoprotein C. Glycoside D. Mucopolysaccharide E. Oligosaccharide The correct answer is- C-  Glycoside. Digoxin is a cardiac glycoside. Glycosides are compounds containing a carbohydrate and a non carbohydrate residue in the same molecule. In these compounds the carbohydrate residue is attached by an acetal linkage...

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Liver cirrhosis and ammonia intoxication

Case details A 55-year-old man suffers from cirrhosis of liver. Toxins such as ammonia are not properly metabolized by the liver in this disease and can damage the organs such as brain. Which of the following amino acids covalently binds ammonia, transports and stores it in a non toxic form? A. Tryptophan B. Alanine C. Aspartate D. Glutamate E. Glutamine The correct answer is- D- Glutamate. Glutamate occupies a central place in the amino acid metabolism. Basically it acts as a collector of amino group of the amino acids. Free ammonia is toxic to the body especially to brain cells;...

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Absorption of dietary glucose

A 45-year-old morbidly obese woman has been attempting to lose weight using a low- carbohydrate diet. After 2 months of little success, she confides in her son that she does add glucose to her coffee in the morning and after dinner but feels only some of this will be absorbed and should not be the cause of her limited success. Her son, a medical student, states that glucose is almost completely absorbed from the gut. What type of transport does glucose utilize for gastro intestinal absorption? A. Active- Carrier mediated, against the concentration gradient and energy dependent B. Facilitated- Carrier...

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Classification of lipoproteins as per density

Chylomicrons, intermediate- density- lipoproteins (IDLs), low- density- lipoproteins (LDLs), and very low-density lipoproteins (VLDLs) are all serum lipoproteins. What is the correct ordering of these particles from the lowest to the highest density? A.LDLs, IDLs, VLDLs and chylomicrons B. Chylomicrons, VLDLs, IDLs, LDLs C.VLDLs, IDLs, LDLs and Chylomicrons D.LDLs, VLDLs, IDLs, Chylomicrons E. Chylomicrons, IDLS, VLDLs and LDLs. The correct answer is B- Chylomicrons, VLDLs, IDLs, LDLs Based on density Lipoproteins can be classified as follows Since fat is less dense than water, the density of a lipoprotein decreases as the proportion of lipid to protein increases.  Lipoproteins with high lipid...

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Mechanism of action of Ciprofloxacin

Case details A 38-year-old woman, who works as an administrative assistant for a large company, opened a package and found a suspicious white powder. Analysis of the powder indicates that it contained traces of the bacterium Bacillus anthracis. The woman was treated with ciprofloxacin, an effective antibiotic. Ciprofloxacin’s mechanism of action is best described as an inhibition of which of the following? A. Bacterial dihydrofolate reductase B. Bacterial peptidyl transferase activity C. Bacterial RNA polymerase D. DNA gyrase E. DNA polymerase III The correct answer is D- DNA gyrase. The quinolones, including nalidixic acid and its fluorinated derivatives (ciprofloxacin, levofloxacin,...

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Case study- Wernicke-Korsakoff syndrome

Case details A 58-year-old man with a history of heavy drinking presents with confusion, unstable gait, and nystagmus. A provisional diagnosis of Wernicke’s- Korsakoff syndrome is made. Which of the patient’s enzymes of the pentose phosphate pathway is inhibited due to vitamin deficiency in this case? A. Transaldolase B. Transketolase C. Glucose-6-P- dehydrogenase D. Epimerase E. Phosphogluconate dehydrogenase The correct answer is B. – Transketolase. Wernicke-Korsakoff syndrome (thiamine deficiency) is often associated with chronic alcoholics. Thiamine deficiency is uncommon except in alcoholics as a result of nutritional deficiencies and malabsorption. The term Wernicke’s encephalopathy is used to describe the clinical...

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Case study- HIV infection

Case details A 25-year-old female is sexually active with a new partner and would like to have an HIV test. The current standard for HIV testing is to start with an enzyme- linked immuno sorbent assay (ELISA). HIV antigens are coated on a plate, and the patient’s serum is added. If the patient has HIV antibodies, binding of these antibodies to the antigens on the plate will be detected. If the ELISA test is positive, a confirmatory test is done. In this confirmatory test, the patient’s serum is added to HIV antigens, which are on a nitrocellulose membrane. This confirmatory...

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Case study- Mutation in complex II of ETC

An -8 year-old boy is seen by an ophthalmologist for difficulties in seeing in all visual fields as well as slow eye movements. The ophthalmologist finds pigmentary retinopathy and ophthalmoplegia. The child is suspected to have Kearns- Sayre syndrome, a disorder due to a mutation in complex II of ETC. The electron transport from which substance would be impaired? A. Malate B. Isocitrate C. Succinate D. Pyruvate E. Alpha Keto glutarate Answer- The correct answer is C- Succinate. Electrons flow through the respiratory chain through a redox span of 1.1 V from NAD+/NADH to O2/2H2O passing through three large protein...

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Biotin deficiency- A case report

Case details A 23-year-old body builder visits his physician with complaints of fatigue, depression, insomnia, hair loss and dry skin. He tells the physician he has been “bulking up” for an upcoming competition, and his meals consist mostly of eight raw eggs along with low-fat milk. The physician suspects biotin deficiency given the patients’ diet and symptoms. Which of the following is biotin required for? A. The formation of cis-retinal B. Transfer of 1-carbon units C. Hydroxylation reactions D. Carboxylation of pyruvate E. Decarboxylation of α-Keto acids Answer- D- Carboxylation of pyruvate is the right answer. Biotin is required for...

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Which of the following statements is correct regarding transcription?

CASE DETAILS A 4-year-old child, on a well-child- check up, is found to have a large flank mass. A computed tomography (CT) scan demonstrates a large mass arising from the kidney, and a subsequent biopsy reveals a diagnosis of Wilm’s tumor. A pediatric oncologist starts chemotherapy containing the transcription inhibitor Actinomycin D. Which of the following statements is correct regarding transcription? A. Eukaryotes often produce polycistronic mRNA B. RNA polymerase requires a primer C. The RNA chain grows in the 3′-5′ direction D. Rho factor is critical for the initiation of RNA transcription E. The TATA box contains a consensus...

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Nucleic acid with modified nucleotides

Case Details A second year medical student looking to match into a competitive residency joins a laboratory studying gene regulation in a mouse model of hepatocellular carcinoma. He isolates nucleic acids from the cells after exposure to a known carcinogen and has the sequence analyzed. He is surprised to find that some of the nucleotides are Pseudouridine and ribothymidine. Which type of nucleic acid has the student likely isolated? A. t RNA B. r RNA C. hn RNA D. m RNA E. sn RNA Answer- The correct answer is- A- t RNA. Transfer RNA s are post transcriptionally modified. Ribothymidine...

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Biochemical basis of difference in the electrophoretic mobilities of Hb A and HbS

Normal hemoglobin (Hb A) and sickle-cell hemoglobin (Hb S) have different electrophoretic mobilities because these two proteins have different what? A. Amount of bound oxygen B. Amount of bound 2, 3 bisphosphoglycerate C. Charges D. Size E. Hydrophobicity Answer- The correct answer is-C- charges. In Sickle cell disease, also called as sickle-cell anemia, a single nucleotide alteration (point mutation) in the β globin gene of hemoglobin causes a change of thymine for adenine (GAG to GTG.), at the sixth codon of the ß gene. This change encodes Valine instead of Glutamic acid in the sixth position on the ß-globin molecule....

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Case study-Hemochromatosis

Case details A 53-year-old man sees his family physician with concerns that his skin is “bronzing”- Figure Figure- Bronze skin and diabetes, a sign of hemochromatosis He is found to have diabetes as well as an elevated ferritin (a sign of iron over load).The physician suspects hemochromatosis and finds the patient carries a mutation where tyrosine is substituted  for cysteine at position 282(C282Y) of the HFE gene. The patient is diagnosed with hemochromatosis, which is a disease that results from which type of mutation? A. Silent B. Missense C. Nonsense D. Frameshift E. Deletion Answer- The correct answer is B-...

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RNA editing in humans

Details A scientist is studying post -transcriptional processing in human stem cells. He clones an unknown segment of DNA to express the gene in culture. However when he sequences the protein, he finds that one of the amino acids does not match the amino acid that would be predicted from the genetic code. After confirmations, he suspects that RNA editing has taken place. Which of the following is an example of RNA editing in humans? A. Production of Calcitonin and Calcitonin related peptide from the same gene B. Production of membrane bound (m Ig M) and secreted (s IgM) from...

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Which of the following is not a characteristic of genetic code?

Which of the following is not a characteristic of genetic code? A. It is a triplet code B. It is non overlapping and without punctuation C. It is nearly universal D. It is degenerate – one code may code for more than one amino acid E. It is unambiguous Answer- The correct answer is D. Genetic code is degenerate, but that does not mean, a given code may code for more than one amino acids. In fact, multiple codons can decode the same amino acid, but vice versa is not true (figure) Genetic Code- Characteristics Specificity- Genetic code is specific...

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Case study- Pneumonia

Case details A 54-year-old man develops a productive cough and a low- grade fever. He visits his family physician who suspects mycoplasma pneumonia. The physician tries to treat the patient empirically with Erythromycin. Which of the following describes the mechanism of Erythromycin? A. Binds to 5′ cap of RNA B. Inhibits the 30S ribosomal RNA C. Binds to the Shine Dalgarno sequence D. Inhibits the initiation factor IF-1 E. Inhibits the 50 S ribosomal subunit. Answer- E-Inhibits the 50 S ribosomal subunit. Ribosomes are large complexes of protein and r RNA. They consist of two subunits one large (Heavy) and one...

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Case study – Urinary Tract infection

Case Details A 30-year-old female presents with burning on urination and blood in her urine. She is diagnosed with a urinary tract infection. She is prescribed an antibiotic that inhibits an enzyme that prevents extreme supercoiling of DNA. Super coiling of DNA results from unwinding at a replication fork. This enzyme breaks and rejoins DNA chains. Which of the following is the most characteristic of this enzyme? A. Helicase B. Single strand binding protein C. Topo isomerase D. DNA polymerase I E. DNA polymerase III Answer- The correct answer is C- Topoisomerase. The Supercoiling is controlled by a remarkable group...

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Case study- Mushroom poisoning ?

Case details Two couples present to the emergency room with severe nausea, vomiting and diarrhea. One of the patients admits that she served salad at the dinner party to which she had added a few mushrooms she picked on a hike earlier. With such information, it is likely that their symptoms are a result of inhibition of which molecular event?  A. Inhibition of RNA polymerase II B. Inhibition of RNA polymerase I C. Inhibition of RNA splicing D. Inhibition of RNA Polyadenylation E. Inhibition of RNA polymerase III Answer- The correct answer is RNA polymerase II. It is a case...

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Medication that acts by activating c GMP ?

Case details A 50-year-old male is brought to the emergency room with chest pain and shortness of breath. He is given a medication that activates cGMP, resulting in relaxation of vascular smooth muscle. This medication is most likely a derivative of: A. Creatine phosphate B. S-Adenosyl Methionine C. Glutathione D. Melatonin E. Nitric oxide Answer- E- Nitric oxide Nitric oxide is a highly reactive gas. It participates in many chemical reactions. Endothelium-derived relaxing factor was originally the name given to several proposed factors causing vasodilatation. The major endothelial derived relaxing factor was later discovered to be nitric oxide (NO). Nitric...

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Phenylketonuria- A case report

Case details A newborn male infant was diagnosed as having phenylketonuria (PKU), and immediately placed on diet low in phenylalanine ; careful compliance with the diet and frequent monitoring of the patient’s plasma Phenyl alanine level resulted in the level being maintained at the lower limit of the normal range. The patient appeared to be developing normally until 4 months of age, when he developed truncal hypotonia and spasticity of the limbs. Despite being on a low-phenylalanine diet, at 5 months the patient had several grand mal (epileptic) seizures. After an abnormal Phenyl alanine-loading test, the patient’s urine was found to...

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Condition causing hypouricemia ?

Which out of the following conditions is associated with hypouricemia? A. Lesch Nyhan syndrome B. Adenosine deaminase deficiency C. Over activity of PRPP synthetase D. Over activity of Amido transferase E. Von Gierke’s disease Answer- The correct answer is Adenosine deaminase deficiency. Adenosine deaminase deficiency, also called ADA deficiency or ADA-SCID is an Autosomal recessive disorder that causes immunodeficiency. It accounts for about 15% of all cases of severe combined immunodeficiency (SCID). The SCID syndrome is characterized by gross functional impairment of both humoral and cell-mediated immunity and by susceptibility to devastating fungal, bacterial, and viral infections. Adenosine deaminase- catalyzes...

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Type 1 Diabetes mellitus – Etiology ?

A 10- year-old child has been diagnosed with Juvenile diabetes mellitus (type 1 diabetes mellitus). This is a disorder of carbohydrate metabolism caused by insulin deficiency. The disease is often preceded by viral infection with inflammation of the beta cells of pancreas, but also exhibits genetic predisposition with a 40-50% concordance rate in monozygotic twins and clustering in families. Type 1 diabetes mellitus may be best described as a A. Sex linked disorder B. Congenital disorder C. Sporadic disorder D. Multifactorial disorder E. Mendelian disorder Answer- The correct answer is- D, Multifactorial disorder. Many common diseases are caused by a combination...

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Co-factor for GABA, Dopamine, and Histamine ?

The neurotransmitters GABA, dopamine, and histamine are all derived from an amino acid precursor. The generation of these neurotransmitters from the appropriate amino acids requires which one of the following cofactors? A. NAD+ B. B1 C. B2 D. B6 E. B12 Answer- The correct answer is B6. All the neurotransmitters in question are derived by a common process of decarboxylation that requires the presence of vitamin B6 as a coenzyme. 1) GABA is derived from Glutamic acid (figure-1) Figure-1- Glutamic acid to GABA conversion. The reaction is catalyzed by glutamic acid decarboxylase that requires the presence of B6-P as a...

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Respiratory Distress syndrome- Case discussion

Case Details An infant is born prematurely at 28 weeks and has developed increasing difficulty in breathing. His skin starts to turn blue from lack of oxygen(cyanosis).He is diagnosed with Respiratory distress syndrome due to deficiency of lung surfactant . Which of the following is the phospholipid of primary importance in surfactant? A. Dipalmitoyl phosphatidyl choline B. Dipalmitoyl phosphatidyl ethanolamine C. Dipalmitoyl phosphoglyceride D. Dipalmitoyl phosphatidyl Inositol E. Dipalmitoyl phosphatidyl serine  Case discussion The correct answer is A- Dipalmitoyl phosphatidyl choline. Respiratory distress syndrome, also known as hyaline membrane disease, occurs almost exclusively in premature infants. Lung surfactant is a...

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Respiratory distress syndrome- A case report

An infant is born prematurely at 28 weeks and has developed increasing difficulty in breathing. His skin starts to turn blue from lack of oxygen(cyanosis).He is diagnosed with Respiratory distress syndrome due to deficiency of lung surfactant . Which of the following is the phospholipid of primary importance in surfactant? A. Dipalmitoyl phosphatidyl choline B. Dipalmitoyl phosphatidyl ethanolamine C. Dipalmitoyl phosphoglyceride D. Dipalmitoyl phosphatidyl Inositol E. Dipalmitoyl phosphatidyl serine Figure- Chest radiograph of an infant with respiratory distress syndrome of the newborn. For case discussion follow the link http://usmle.biochemistryformedics.com/respiratory-distress-syndrome-case-discussion/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every...

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Familial hypercholesterolemia- Case discussion

Case Details In familial hypercholesterolemia, cholesterol is deposited in various tissues because of the high concentration of LDL cholesterol in the plasma. Of particular concern is the oxidation of the excess blood LDL to form oxidized LDL (oxLDL). The oxLDL is taken up by immune-system cells called macrophages, which become engorged to form foam cells. Which statement best describes the formation of foam cells? A. LDL receptors on peripheral cells are upregulated B. LDL receptors for modified LDL (Ox LDL) are not down regulated C. LDL enters by pinocytosis to form foam cells D. There is increased de no synthesis...

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Familial hypercholesterolemia- A case report

Case Details In familial hypercholesterolemia, cholesterol is deposited in various tissues because of the high concentration of LDL cholesterol in the plasma. Of particular concern is the oxidation of the excess blood LDL to form oxidized LDL (oxLDL). The oxLDL is taken up by immune-system cells called macrophages, which become engorged to form foam cells. Which statement best describes the formation of foam cells? A. LDL receptors on peripheral cells are upregulated B. LDL receptors for modified LDL (Ox LDL) are not down regulated C. LDL enters by pinocytosis to form foam cells D. There is increased de no synthesis...

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Case discussion- Treatment with Hydroxyurea- A case of chronic myelogenous Leukemia

Case Details A physician evaluates a 32-year-old patient for fatigue. The patient is found to have an elevated white blood cell count and an enlarged spleen. A referral to an oncologist results in a diagnosis of chronic myelogenous leukemia. Treatment with hydroxyurea, a ribonucleotide reductase inhibitor is begun. The normal functioning of this enzyme is to do which of the followings? A. Converts xanthine to uric acid B. Converts ribonucleotides to deoxy ribonucleotides C. Degrades guanine to xanthine D. Degrades AMP to IMP E. Converts PRPP to phosphoribosylamine Answer- The correct answer is- B Hydroxyurea is prescribed to the patients...

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Treatment with hyrdroxyurea- A case of chronic myelogenous leukemia

A physician evaluates a 32-year-old patient for fatigue. The patient is found to have an elevated white blood cell count and an enlarged spleen. A referral to an oncologist results in a diagnosis of chronic myelogenous leukemia. Treatment with hydroxyurea, a ribonucleotide reductase inhibitor is begun. The normal functioning of this enzyme is to do which of the followings ? a) Converts xanthine to uric acid b) Converts ribonucleotides to deoxy ribonucleotides c) Degrades guanine to xanthine d) Degrades AMP to IMP e) Converts PRPP to phosphoribosylamine   Figure- Blood film of a patient suffering from Chronic myelogenous leukemia For...

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Megaloblastic anemia in the presence of normal Folic acid and Vitamin B12- Case discussion

Case details A 6-month-old infant is seen by the pediatrician for developmental delay. Blood work shows megaloblastic anemia, although measurements of B12 and folate are in the high normal range. Urinalysis demonstrates, upon standing, the formation of a crystalline substance. Supplementation of the child’s diet with uridine reversed virtually all of the clinical problems. The crystalline substance was most likely composed of which of the following? A. Uracil B. Thymine C. Orotate D. Aspartate E. Cytosine Answer- The correct answer is C-Orotate. The child seems to be suffering from Hereditary orotic aciduria. Orotic aciduria refers to an excessive excretion of orotic acid...

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Megaloblastic anemia in the presence of normal Folic acid and B12- A case report

Case details A 6-month-old infant is seen by the pediatrician for developmental delay. Blood work shows megaloblastic anemia, although measurements of B12 and folate are in the high normal range. Urinalysis demonstrates, upon standing, the formation of a crystalline substance. Supplementation of the child’s diet with uridine reversed virtually all of the clinical problems. The crystalline substance was most likely composed of which of the following? A. Uracil B. Thymine C. Orotate D. Aspartate E. Cytosine   Figure- Megaloblastic anemia and macrocytosis To check the answer follow the link http://usmle.biochemistryformedics.com/megaloblastic-anemia-in-the-presence-of-normal-folic-acid-and-vitamin-b12-case-discussion/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time...

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Methotrexate therapy- Case discussion

Case details A 60-year-old female patient has psoriasis and has been treated with methotrexate for several years. She has no other medical problems and her preventive screenings, including fecal occult blood tests and colonoscopy, have all been normal. She has developed an anemia. Which of the following would you expect to find when working up her anemia? A. A macrocytic anemia B. A microcytic anemia C. Thalassemia D. Spherocytosis E. A low vitamin B12 level Answer- The correct answer is- A, Macrocytic anemia. Methotrexate is an antimetabolite, it is recommended as a treatment for psoriasis to inhibit cellular proliferation. It...

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Methotrexate therapy- A case report

A 60-year-old female patient has psoriasis and has been treated with methotrexate for several years. She has no other medical problems and her preventive screenings, including fecal occult blood tests and colonoscopy, have all been normal. She has developed an anemia. Which of the following would you expect to find  when working up her anemia? A. A macrocytic anemia B. A microcytic anemia C. Thalassemia D. Spherocytosis E. A low vitamin B12 level For answer follow the link http://usmle.biochemistryformedics.com/methotrexate-therapy-case-discussion/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Answer- Case study- Hypoglycemia and Hepatomegaly

A female infant appeared normal at birth but developed signs of liver disease and muscular weakness at 3 months. She had periods of hypoglycemia, particularly on awakening. Examination revealed an enlarged liver. Laboratory analyses following fasting revealed ketoacidosis, blood pH 7.25, and elevations in both alanine transaminase (ALT) and aspartate transaminase (AST). Administration of glucagon following a carbohydrate meal elicited a normal rise in blood glucose, but glucose levels did not rise when glucagon was administered following an overnight fast. Liver biopsy revealed an increase in the glycogen content (6 percent of wet weight). In which of the following enzymes...

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Case study- Hypoglycemia and Hepatomegaly

QUESTION OF THE DAY A female infant appeared normal at birth but developed signs of liver disease and muscular weakness at 3 months. She had periods of hypoglycemia, particularly on awakening. Examination revealed an enlarged liver. Laboratory analyses following fasting revealed ketoacidosis, blood pH 7.25, and elevations in both alanine transaminase (ALT) and aspartate transaminase (AST). Administration of glucagon following a carbohydrate meal elicited a normal rise in blood glucose, but glucose levels did not rise when glucagon was administered following an overnight fast. Liver biopsy revealed an increase in the glycogen content (6 percent of wet weight). In which...

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Case study- Lactose Intolerance

Case details A 30- year-old Asian male presents with bloating, abdominal cramps, and diarrhea. He states that he develops these symptoms whenever he drinks milk or eat dairy products. He is diagnosed with lactose intolerance, a common condition in which lactose is not digested normally and accumulates in the gut. Lactase converts lactose into : A. Two glucose molecules B. Glucose and Fructose C. Glucose and Galactose D. Fructose and Galactose E. Sucrose and Maltose Answer- The correct answer is C- Glucose and galactose. Lactose is a disaccharide made up of Galactose and glucose residues  linked together by beta 1-4...

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Case study- Lactose intolerance

QUESTION OF THE DAY A 30- year-old Asian male presents with bloating, abdominal cramps, and diarrhea. He states that he develops these symptoms whenever he drinks milk or eat dairy products. He is diagnosed with lactose intolerance, a common condition in which lactose is not digested normally and accumulates in the gut. Lactase converts lactose into : A. Two glucose molecules B. Glucose and Fructose C. Glucose and Galactose D. Fructose and Galactose E. Sucrose and Maltose For answer- follow the link http://usmle.biochemistryformedics.com/answer-case-study-lactose-intolerance/   Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank...

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Answer- Case study- Breast lump

A 23-year-old woman is seen for a lump in her breast that she palpated on self breast examination. History reveals that her mother and her aunt both had breast and ovarian cancer. Given this presentation, it is suspected that the patient might be having a mutation in which of the following genes involved in DNA repair? A. BRCA-1 B. p53 C. Rb D. p10 E. ras Answer- The correct answer is- A. BRCA- 1 gene is implicated in breast and ovarian cancer. A major cause of familial breast cancer results from mutation in the breast cancer susceptibility gene, BRCA1. BRCA1...

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Case study- Breast lump

Question of the day A 23-year-old woman is seen for a lump in her breast that she palpated on self breast examination. History reveals that her mother and her aunt both had breast and ovarian cancer. Given this presentation, it is suspected that the patient might be having a mutation in which of the following genes involved in DNA repair? A. BRCA-1 B. p53 C. Rb D. p10 E. ras   Figure- Breast lump For answer, follow the link http://usmle.biochemistryformedics.com/answer-case-study-breast-lump/   Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Answer- Case study- Epilepsy

Question of the day A 12-year-old boy develops convulsions. After running an electroencephalogram (EEG), a neurologist determines that the child has epilepsy. He is started on Benzodiazepine, which promotes the activity of GABA. GABA is derived from the amino acid glutamate via which of the following biochemical reactions? A. Deamination B. Decarboxylation C. Hydroxylation D. Iodination E. Methylation Answer- The correct answer is B- Decarboxylation, Glutamic acid undergoes decarboxylation to yield GABA. The reaction is catalyzed by Glutamic acid decarboxylase that requires vitamin B6-P as a coenzyme. GABA is an inhibitory neurotransmitter and is thus helpful in controlling convulsions. Deamination...

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Case study- Epilepsy-A 12-year-old boy develops convulsions..

Question of the day A 12-year-old boy develops convulsions. After running an electroencephalogram (EEG), a neurologist determines that the child has epilepsy. He is started on Benzodiazepine, which promotes the activity of GABA . GABA is derived from the amino acid glutamate via which of the following biochemical reactions ? A. Deamination B. Decarboxylation C. Hydroxylation D. Iodination E. Methylation Figure- Benzodiazepines  bind to the gamma sub-unit of the GABA-A receptor. Their binding causes an allosteric (structural) modification of the receptor that results in an increase in GABA A receptor activity. Benzodiazepines do not substitute for GABA, which bind at the...

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Answer to the question- Amino acids in the post absorptive state ..

During a medical rotation, a medical student volunteered for a respiratory physiology exam that determines basal metabolic rate and the respiratory quotient. She followed the protocol for a resting individual in the post absorptive state. Which of the following amino acids would be found in the highest concentration in serum? A. Alanine and Glutamine B. Arginine and Ornithine C. Glutamate and Aspartate D. Branched chain amino acids E. Hydrophobic amino acids Answer- A- Alanine and Glutamine. Post absorptive state is the state of the body 3-5 hours after meals. It is that period of time in the body during which...

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Amino acids in the post absorptive state ?

Question of the day During a medical rotation, a medical student volunteered for a respiratory physiology exam that determines basal metabolic rate and the respiratory quotient. She followed the protocol for a resting individual in the post absorptive state. Which of the following amino acids would be found in the highest concentration in serum? A. Alanine and Glutamine B. Arginine and Ornithine C. Glutamate and Aspartate D. Branched chain amino acids E. Hydrophobic amino acids   Figure- Post absorptive state For answer follow the link http://usmle.biochemistryformedics.com/answer-to-the-question-amino-acids-in-the-post-absorptive-state/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit...

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Answer- Case study- Hyperammonemia and orotic aciduria

A newborn becomes lethargic and drowsy 24 hour after birth. Blood analysis shows hyperammonemia, coupled with Orotic aciduria. This individual has an enzyme deficiency that leads to an inability to directly produce which of the following? A. Carbamoyl phosphate B. Ornithine C. Citrulline D. Argininosuccinate E. Arginine Answer- The correct answer is -C-Citrulline. Orotic aciduria refers to an excessive excretion of Orotic acid in urine. This is a disorder of pathway of pyrimidine biosynthesis inherited in an autosomal recessive manner. Increased excretion of orotic acid, uracil, and uridine also accompanies a deficiency in liver mitochondrial ornithine transcarbamoylase, an enzyme of...

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Case study- Hyperammonemia and Orotic aciduria

Question of the day A newborn becomes lethargic and drowsy 24 hour after birth. Blood analysis shows hyperammonemia, coupled with Orotic aciduria. This individual has an enzyme deficiency that leads to an inability to directly produce which of the following? A. Carbamoyl phosphate B. Ornithine C. Citrulline D. Argininosuccinate E. Arginine   Figure- Structure of Orotic acid For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-hyperammonemia-and-orotic-aciduria/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Answer- Case study- Oral contraceptives induced vitamin deficiencies

Case Details Oral contraceptives are known to lower blood levels of folate and vitamin B6. Which of the following conversion processes might be directly affected? A. Ornithine to Citrulline B. Histidine to histamine C. Glutamate to Glutamine D. Propionyl co A to Methyl malonyl co A E. Phenyl alanine to Tyrosine Answer- B- The correct answer is conversion of Histidine to histamine. The reaction is catalyzed by decarboxylase that requires B6-P as a cofactor (Figure-1) that gets deficient in women upon long-term oral contraceptive usage. Folic acid is not required in this reaction. Figure-1- Decarboxylation of Histidine is carried out...

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Case- Oral contraceptive induced Vitamin deficiencies

Question of the day Oral contraceptives are known to lower blood levels of folate and vitamin B6. Figure- Oral contraceptives Which of the following conversion processes might be directly affected ? A. Ornithine to Citrulline B. Histidine to histamine C. Glutamate to Glutamine D. Propionyl co A to Methyl malonyl co A E. Phenyl alanine to Tyrosine For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-oral-contraceptives-induced-vitamin-deficiencies/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Answer- Case study- Primaquine induced hemolytic anemia

Question of the day A 20-year-old, African-American male military recruit is about to be sent on his assignment. In preparation for his tour of duty, he is given a prophylactic dose of primaquine to prevent malaria. Several days after he begins taking the drug, he develops fatigue and hemolytic anemia. Which of the following enzymes is likely deficient? A. Galactokinase B. Fructokinase C. Glucose-6-P dehydrogenase D. Pyruvate kinase E. Aldolase B Answer- The correct answer is- C-Glucose-6-P dehydrogenase deficiency The patient has presented with primaquine induced hemolytic anemia. Primaquine is an antimalarial drug known to trigger an attack of hemolysis...

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Case study- Primaquine induced hemolytic anemia

Question of the day A 20-year-old, African-American male military recruit is about to be sent on his assignment. In preparation for his tour of duty, he is given a prophylactic dose of primaquine to prevent malaria. Several days after he begins taking the drug, he develops fatigue and hemolytic anemia. Which of the following enzymes is likely deficient? A. Galactokinase B. Fructokinase C. Glucose-6-P dehydrogenase D. Pyruvate kinase E. Aldolase B For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-primaquine-induced-hemolytic-anemia/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Answer- Case study- Urea cycle disorder

Case details A 2-year-old girl was seen in the emergency room for vomiting and tremors. The elevated plasma ammonium ion concentration was 200 μM/L (normal 11-40 μM/L). Metabolic screens of blood and serum were ordered and were remarkable for an elevation in the amino acid arginine in serum. Which of the following enzymes would most likely cause an elevation in the plasma Arginine levels? A. Carbamoyl phosphate synthetase I B. Carbamoyl phosphate synthetase II C. Ornithine transcarbamoylase D. Arginase E. Argino succinate lyase Answer- The correct answer is D- Arginase Arginine is an intermediate of urea cycle. Its high concentration...

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Case study- Ammonia Intoxication-A 2-year-old girl was seen in the emergency room ..

Question of the day A 2-year-old girl was seen in the emergency room for vomiting and tremors. The elevated plasma ammonium ion concentration was 200 μM/L (normal 11-40 μM/L). Metabolic screens of blood and serum were ordered and were remarkable for an elevation in the amino acid arginine in serum. Which of the following enzymes would most likely cause an elevation in the plasma Arginine levels? A. Carbamoyl phosphate synthetase I B. Carbamoyl phosphate synthetase II C. Ornithine transcarbamoylase D. Arginase E. Argino succinic acid lyase Figure- Structure of Arginine For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-urea-cycle-disorder/ Please help Biochemistry for...

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Answer- Case study- HIV infection- A 33 -year-old, homosexual man..

Case details A 33 -year-old, homosexual man is recently diagnosed with human immuno deficiency virus (HIV) infection. His CD4+T- cell count is dramatically decreased, and he has a high HIV viral load. He is referred to an infectious disease clinic where they begin him on a nucleoside analog. These drugs inhibit DNA synthesis because they lack which of the following properties required for the normal DNA polymerization? A. 5′- phosphate B. 3′ – hydroxyl C. 7- methyl guanosine triphosphate D. Poly (A) tail E. A consensus sequence Answer- The correct option is B) – 3′-hydroxyl group .The replication proceeds with...

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Case study- HIV infection – A 33 -year-old, homosexual man is recently diagnosed..

Question of the day A 33 -year-old, homosexual man is recently diagnosed with human immuno deficiency virus (HIV) infection. His CD4+T- cell count is dramatically decreased, and he has a high HIV viral load.   Figure- A cross sectional view of HIV structure He is referred to an infectious disease clinic where they begin him on a nucleoside analog. These drugs inhibit DNA synthesis because they lack which of the following properties required for the normal DNA polymerization? A. 5′- phosphate B. 3′ – hydroxyl C. 7- methyl Guanosine triphosphate D. Poly (A) tail E. A consensus sequence For answer...

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Case study- Achlorhydria (Discussion)

A 65- year-old woman is evaluated by a gastroenterologist for progressive signs and symptoms of malnutrition. Throughout her work up, she is found to have significantly decreased stomach acid. She is also found to have antibodies to gastric parietal cells, which are normally responsible for the production of acid. Why is hydrochloric acid important in digestion? A. It stimulates the cleavage of trypsinogen to trypsin B. It is required for the activity of α- Amylase C. It converts pepsinogen to pepsin D. It is required for lipid digestion E. It drives the secondary transport of amino acids Answer- The correct...

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Case study- Achlorhydria-A 65- year-old woman is evaluated by a gastroenterologist

Question of the day A 65- year-old woman is evaluated by a gastroenterologist for progressive signs and symptoms of malnutrition. Throughout her work up, she is found to have significantly decreased stomach acid. She is also found to have antibodies to gastric parietal cells, which are normally responsible for the production of acid. Why is hydrochloric acid important in digestion? A. It stimulates the cleavage of trypsinogen to trypsin B. It is required for the activity of α- Amylase C. It converts pepsinogen to pepsin D. It is required for lipid digestion E. It drives the secondary transport of amino...

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Answer- Case study- Chronic Alcoholism- A 75-year-old chronic alcoholic presents to the emergency room…

A 75-year-old chronic alcoholic presents to the emergency room after being found on the rail road tracks passed out. On examination, he is found to have a distended abdomen that is equivalent in size to a full term pregnant woman’s belly. Which of the following functions of the liver has been compromised to cause this finding? A. Lipid metabolism B. Albumin synthesis C. Bilirubin metabolism D. Alcohol detoxification E. Decreased production of coagulation factors Answer- The right answer is B- Albumin synthesis. The patient has alcoholic liver disease. Excessive alcohol intake can lead to fatty liver, hepatitis, and cirrhosis (figure)....

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Case study- Chronic Alcoholism-A 75-year-old chronic alcoholic presents to the emergency room..

QUESTION OF THE DAY A 75-year-old chronic alcoholic presents to the emergency room after being found on the rail road tracks passed out. On examination, he is found to have a distended abdomen that is equivalent in size to a full term pregnant woman’s belly. Which of the following functions of the liver has been compromised to cause this finding? A. Lipid metabolism B. Albumin synthesis C. Bilirubin metabolism D. Alcohol detoxification E. Decreased production of coagulation factors For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-chronic-alcoholism-a-75-year-old-chronic-alcoholic-presents-to-the-emergency-room/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank...

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Answer- Case study- Gestational Diabetes Mellitus and Neonatal hypoglycemia-A patient who had gestational diabetes has just delivered …

A patient who had gestational diabetes has just delivered a 10 lb baby. The baby appears “jittery” and heel stick glucose is 30 mg/dL. Which of the following mechanisms is the explanation for the newborn’s hypoglycemia? A. The mother’s relative hyperinsulinemia B. The baby’s relative hyperinsulinemia C. The mother’s hyperglycemia D. The baby’s hyperglycemia E. Placental insulin production Answer- The correct answer is- B- The baby’s relative hyperinsulinemia. Gestational diabetes is a condition characterized by high blood glucose levels that is first recognized during pregnancy. The condition occurs in approximately 4% of all pregnancies. Almost all women have some degree...

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Case study- Gestational Diabetes and neonatal hypoglycemia-A patient who had gestational diabetes has just delivered ..

A patient who had gestational diabetes has just delivered a 10 lb baby. The baby appears “jittery” and a heel stick glucose is 30 mg/dL. Which of the following mechanisms is the explanation for the newborn’s hypoglycemia ? A. The mother’s relative hyperinsulinemia B. The baby’s relative hyperinsulinemia C. The mother’s hyperglycemia D. The baby’s hyperglycemia E. Placental insulin production For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-gestational-diabetes-mellitus-and-neonatal-hypoglycemia-a-patient-who-had-gestational-diabetes-has-just-delivered/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Answer case study- Exophthalmos- A 50-year-old woman complains of feeling warm all the time…

Case details A 50-year-old woman complains of feeling warm all the time. Her eyes appear as they are bulging out of their sockets (exophthalmos). She sees a family physician to evaluate her condition. Her labs demonstrate a decreased level of TSH. Which of the following would you expect in this patient? A. Reduced blood pressure B. Weight gain C. Increased basal metabolic rate D. Reduced heart rate E. Excess sleep Answer- The patient presents with signs and lab reports consistent with hyperthyroidism (thyrotoxicosis). Hence the right option is – C- Increased basal metabolic rate.Thyroid hormone is an important regulator of basal...

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Weekly Plan- From 28/01- 03/02- 2014

28/01/2014- Tuesday- Endocrinology 29/01/2014- Wednesday- Diabetes Mellitus and Metabolic syndrome 30/01/2014- Thursday- Integrative metabolism 31/01/2014- Friday- Biochemistry of Digestion 01/02/2014- Saturday- DNA Replication and Transcription o2/02/2014- Sunday- Amino acid catabolism 03/02/2014- Monday- Metabolism of carbohydrates   Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Case study- Exophthalmos- A 50-year-old woman complains of feeling warm …

QUESTION OF THE DAY A 50-year-old woman complains of feeling warm all the time. Her eyes appear as they are bulging out of their sockets (exophthalmos). She sees a family physician to evaluate her condition. Her labs demonstrate a decreased level of TSH. Which of the following would you expect in this patient ? A. Reduced blood pressure B. Weight gain C. Increased basal metabolic rate D. Reduced heart rate E. Excess sleep For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-exophthalmos-a-50-year-old-woman-complains-of-feeling-warm-all-the-time/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Answer- Case study- DNA Replication- A scientist is replicating human DNA in a test tube…

A scientist is replicating human DNA in a test tube and has added intact DNA, the replisome complex, and the four deoxyribonucleoside triphosphates. To the surprise of the scientist, there was no DNA synthesized, as determined by the incorporation of radio-labeled precursors into acid-precipitable material. The scientist’s failure to synthesize DNA is most likely due to a lack of which of the following in his reaction mixture? A. Reverse transcriptase B. Ribonucleoside triphosphates C. Templates D. Dideoxynucleoside triphosphates E. Sigma factor The answer is B: Ribonucleoside triphosphates. DNA Replication is the basis for inheritance. It is the fundamental process occurring in...

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Case study- Replication-A scientist is replicating human DNA in a test tube ..

QUESTION OF THE DAY A scientist is replicating human DNA in a test tube and has added intact DNA, the replisome complex, and the four deoxyribonucleoside triphosphates.   Figure- DNA Replication To the surprise of the scientist, there was no DNA synthesized, as determined by the incorporation of radio-labeled precursors into acid-precipitable material. The scientist’s failure to synthesize DNA is most likely due to a lack of which of the following in his reaction mixture? A. Reverse transcriptase B. Ribonucleoside triphosphates C. Templates D. Dideoxynucleoside triphosphates E. Sigma factor For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-dna-replication-a-scientist-is-replicating-human-dna-in-a-test-tube/ Please help Biochemistry for Medics...

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Answer-Case study- Sickle cell disease-A 15-year-old African-American female presents to the emergency room ..

A 15-year-old African-American female presents to the emergency room with complaints of bilateral thigh and hip pain. The pain has been present for 1 day and is steadily increasing in severity. Acetaminophen and ibuprofen have not relieved her symptoms. She denies any recent trauma or excessive exercise. She does report feeling fatigued and has been having burning with urination along with urinating frequently. She reports having similar pain episodes in the past, sometimes requiring hospitalization. On examination, she is afebrile (without fever) and in no acute distress. No one in her family has similar episodes. Her conjunctiva and mucosal membranes...

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Case study- Sickle cell disease-A 15-year-old African-American female presents to the emergency room…

A 15-year-old African-American female presents to the emergency room with complaints of bilateral thigh and hip pain. The pain has been present for 1 day and is steadily increasing in severity. Acetaminophen and ibuprofen have not relieved her symptoms. She denies any recent trauma or excessive exercise. She does report feeling fatigued and has been having burning with urination along with urinating frequently. She reports having similar pain episodes in the past, sometimes requiring hospitalization. On examination, she is afebrile (without fever) and in no acute distress. No one in her family has similar episodes. Her conjunctiva and mucosal membranes...

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Significance of km

ENZYMOLOGY A teenager finishes eating a hot fudge sundae and a milk shake. As her blood sugar rises, the liver recruits both Glucokinase (km = 10.0m M) and Hexokinase (km = 0.10 mM) to metabolize the glucose. Which of the following is a correct statement about the kinetics of these two enzymes? A. Hexokinase will metabolize 100 times more glucose molecules B. Hexokinase will lower the energy of activation more than glucokinase C. Hexokinase has a much higher affinity to glucose than glucokinase D. Hexokinase will have a higher Vmax than glucokinase E. Hexokinase will be induced more than glucokinase...

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Case study- Enzymology- A teenager finishes eating a hot fudge sundae and a milk shake…

ENZYMOLOGY A teenager finishes eating a hot fudge sundae and a milk shake. As her blood sugar rises, the liver recruits both Glucokinase (km = 10.0m M) and Hexokinase (km = 0.10mM) to metabolize the glucose. Which of the following is a correct statement about the kinetics of these two enzymes? A. Hexokinase will metabolize 100 times more glucose molecules B. Hexokinase will lower the energy of activation more than glucokinase C. Hexokinase has a much higher affinity to glucose than glucokinase D. Hexokinase will have a higher Vmax than glucokinase E. Hexokinase will be induced more than glucokinase by...

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Answer- Case study- Amino acid supplements- A 27- year-old, semiprofessional tennis player seeks advice from a hospital-based nutritionist…

AMINO ACID METABOLISM A 27- year-old, semiprofessional tennis player seeks advice from a hospital-based nutritionist concerning his diet supplements. His coach had given him amino acid supplements consisting of phenyl alanine and tyrosine. The rationale was that these precursors to several neurotransmitters will “help his brain focus” on his game. In reality, the excess amino acids are used for energy, with a poor and eclectic diet. Phenyl alanine upon metabolism enters TCA cycle as which of the following? A. Oxaloacetate B. Fumarate C. Succinyl co A D. Citrate E. α- Keto glutarate Answer- The right answer is B- Fumarate. Phenyl...

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Case study- Amino acid supplements-A 27- year-old, semiprofessional tennis player seeks advice from a hospital-based nutritionist concerning his diet…

QUESTION OF THE DAY AMINO ACID METABOLISM A 27- year-old, semiprofessional tennis player seeks advice from a hospital-based nutritionist concerning his diet supplements. His coach had given him amino acid supplements consisting of phenyl alanine and tyrosine. The rationale was that these precursors to several neurotransmitters will “help his brain focus” on his game. Figure- Amino acid supplements In reality, the excess amino acids are used for energy, with a poor and eclectic diet. Phenyl alanine upon metabolism enters TCA cycle as which of the following? A. Oxaloacetate B. Fumarate C. Succinyl co A D. Citrate E. α- Keto glutarate...

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Answer- Case study-Jamaican Sickness- A 35-year-old man in New York City, originally from Jamaica, purchased an illegally imported fruit from a street vendor….

QUESTION OF THE DAY A 35-year-old man in New York City, originally from Jamaica, purchased an illegally imported fruit from a street vendor and, within 4 hours of eating the fruit, began vomiting severely. When brought to the emergency department the man was severely dehydrated and exhibited several seizures. The toxic effects of the fruit were interfering with which of the following? A. Fatty acid release from the adipocytes B. Fatty acid entry into the liver cell C. Fatty acid activation D.Fatty acid oxidation E. Oxidative phosphorylation Answer- D- Fatty acid oxidation. The patient is suffering from Jamaican vomiting sickness....

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Case study- Jamaican Sickness-A 35-year-old man in New York City, originally from Jamaica

METABOLISM OF LIPIDS QUESTION OF THE DAY A 35-year-old man in New York City, originally from Jamaica, purchased an illegally imported fruit from a street vendor and, within 4 hour of eating the fruit, began vomiting severely. When brought to the emergency department the man was severely dehydrated and exhibited several seizures. Figure- Jamaican fruit (Ackee fruit) The toxic effects of the fruit were interfering with which of the following? A. Fatty acid release from the adipocytes B. Fatty acid entry into the liver cell C. Fatty acid activation D.Fatty acid oxidation E. Oxidative phosphorylation For answer, Follow the link...

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Answer- Case study- Hartnup disease- A 28- year-old man complains of a rash on his sun- exposed skin, diarrhea and loss of balance..

A 28- year-old man complains of a rash on his sun- exposed skin, diarrhea and loss of balance. His urinalysis results are significant for an increase in neutral amino acids. The patient is diagnosed with Hartnup’s disease that occurs due to a defective transport of neutral amino acids in the kidney. Apart from tryptophan which of the following amino acids would have been found in urine? A. Lysine B. Arginine C. Histidine D. Phenyl alanine E. Glutamic acid Answer The right option is D- Phenyl alanine. Hartnup disease is an autosomal recessive disorder caused by impaired neutral (i.e., mono amino...

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Case study- Hartnup’s disease- A 28- year-old man complains of a rash on his sun exposed skin, diarrhea and ..

22/01/2014 Amino acid chemistry QUESTION OF THE DAY A 28- year-old man complains of a rash on his sun exposed skin, diarrhea and loss of balance. His urinalysis results are significant for an increase in neutral amino acids. The patient is diagnosed with Hartnup’s disease that occurs due to  defective transport of neutral amino acids in the kidney. Apart from tryptophan which of the following amino acids would have been found in urine? A. Lysine B. Arginine C. Histidine D. Phenyl alanine E. Glutamic acid Figure- Patient with hartnup disease showing pellagra like rashes For answer- Follow the link http://usmle.biochemistryformedics.com/answer-case-study-hartnup-disease-a-28-year-old-man-complains-of-a-rash-on-his-sun-exposed-skin-diarrhea-and-loss-of-balance/...

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Case study- Cholera

 Case study Cholera A 21- year old female working in a rural school suddenly began to pass profuse watery stools almost continuously. She soon started to vomit, her general condition declined abruptly, and she was rushed to the general hospital. On admission she was cyanotic, skin turgor was poor, blood pressure was 70/50 mm Hg and her pulse was rapid and weak. The doctor on duty diagnosed cholera .The stool sample was taken for culture and the treatment was started immediately. Which type of lipid is a receptor for cholera toxin in the intestine? A. GM2 Ganglioside B.GM1 Ganglioside C....

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About the Author- Biochemistry for Medics-Clinical Cases

Dr. Namrata Chhabra is a distinguished Senior-Level Medical Biochemistry Professional with extensive clinical, instructional, research, and administrative experience within prestigious institutions. Over the course of her career she has developed and conducted numerous courses focused on Chemistry, Biochemistry, Research & Analysis, and various other topics. She carries an award-winning track record in conducting high-caliber research, with complementary qualifications in quality management systems and medical laboratory auditing. She has proven herself committed to improving learning experiences for diverse student populations through strategic administrative leadership and curriculum development. She also serves on various academic and extracurricular committees. She also possesses a lengthy...

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Case study- Cholera – A 21- year old female working in a rural school suddenly began to pass profuse watery stools …

21/01/2014 CHEMISTRY OF LIPIDS QUESTION OF THE DAY A 21- year old female working in a rural school suddenly began to pass profuse watery stools almost continuously. She soon started to vomit, her general condition declined abruptly, and she was rushed to the general hospital. On admission she was cyanotic, skin turgor was poor, blood pressure was 70/50 mm Hg and her pulse was rapid and weak. The doctor on duty diagnosed cholera .The stool sample was taken for culture and the treatment was started immediately. Which type of lipid is a receptor for cholera toxin in the intestine? A....

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Answer- DNA Structure-A sample of human DNA is subjected to increasing temperature

QUESTION A sample of human DNA is subjected to increasing temperature until the major fraction exhibits optical density changes due to disruption of its helix (melting or denaturation). A smaller fraction is atypical in that it requires a much higher temperature for melting. This smaller, atypical fraction of DNA must contain a higher content of A. Adenine plus Cytosine B. Cytosine plus Guanine C. Adenine plus Thymine D. Cytosine plus Thymine E. Adenine plus Guanine Answer-The answer is- B- Cytosine plus Guanine. Deoxyribonucleic acid (DNA) is the chemical basis of heredity and is organized into genes, the fundamental units of...

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Question of the day- DNA structure

A sample of human DNA is subjected to increasing temperature until the major fraction exhibits optical density changes due to disruption of its helix (melting or denaturation). A smaller fraction is atypical in that it requires a much higher temperature for melting. This smaller, atypical fraction of DNA must contain a higher content of A. Adenine plus Cytosine B. Cytosine plus Guanine C. Adenine plus Thymine D. Cytosine plus Thymine E. Adenine plus Guanine Figure- DNA Structure For answer follow the link http://usmle.biochemistryformedics.com/answer-dna-structure-a-sample-of-human-dna-is-subjected-to-increasing-temperature/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Weekly Plan (from 21-27/01/2014)

21/01/2014- Tuesday-Chemistry of Lipids 22/01/2014 – Wednesday- Chemistry of amino acids, peptides and protein 23/01/2014- Thursday- Metabolism of Lipids 24/01/2014- Friday- Metabolism of amino acids 25/01/2014- Saturday- Enzymology 26/01/2014- Sunday- Hemoglobinopathies 27/01/2014- Monday- Molecular Biology Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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Porphyria – A case discussion

QUESTION OF THE DAY A 21-year-old young woman, who recently began taking birth control pills, presents to the emergency room with cramping abdominal pain, anxiety, paranoia, and hallucinations. A surgical evaluation, including ultrasound and computed tomography (CT) scan, fails to demonstrate an acute abdominal process. A urinalysis reveals an increase in urine porphyrins. Which of the following is the most likely defect? A. Congenital erythropoietic porphyria B. Variegate porphyria C. Porphyria cutanea tarda D. Acute intermittent porphyria E. Erythropoietic porphyria Answer- D- Acute intermittent porphyria; the patient is suffering from acute intermittent porphyria as  is evident from the clinical manifestations-...

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Case study- Porphyria

19/01/2014 Heme metabolism  Heme synthesis Heme biosynthesis involves eight enzymatic steps in the conversion of glycine and succinyl-CoA to heme (figure). The first and last three enzymes in the pathway are located in the mitochondrion, whereas the other four are in the cytosol. Heme is required for a variety of hemoproteins such as hemoglobin, myoglobin, respiratory cytochromes, and the cytochrome P450 enzymes (CYPs). Hemoglobin synthesis in erythroid precursor cells accounts for approximately 85% of daily heme synthesis in humans. Hepatocytes account for most of the rest, primarily for synthesis of CYPs, which are especially abundant in the liver endoplasmic reticulum,...

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‘Hereditary fructose Intolerance’- Case discussion

QUESTION OF THE DAY A 3-month-old girl is brought to the pediatrician due to fussiness and lethargy. According to the parents, the baby was just fine until the mother needed to return to work, and the baby was being switched from breast milk to baby foods, formula, and fruit juices. At that time, the child cried while feeding, sometimes vomited, and had been lethargic. The baby’s appetite seemed to have worsened. The parents thought that if only formula was used, the baby was better, but they really could not remember. Which possible enzyme defect might lead to this case presentation?...

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Case study- Metabolic disorder- A 3-month-old girl is brought to the pediatrician due to fussiness and lethargy….

QUESTION OF THE DAY A 3-month-old girl is brought to the pediatrician due to fussiness and lethargy. According to the parents, the baby was just fine until the mother needed to return to work, and the baby was being switched from breast milk to baby foods, formula, and fruit juices. At that time, the child cried while feeding, sometimes vomited, and had been lethargic. The baby’s appetite seemed to have worsened. The parents thought that if only formula was used, the baby was better, but they really could not remember. Which possible enzyme defect might lead to this case presentation?...

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Case study- Pellagra

QUESTION OF THE DAY A 56 – year-old male on Isoniazid therapy for tuberculosis has developed rashes on the exposed parts of the body. History is also suggestive of disoriented memory and diarrhea. The patient has been diagnosed with pellagra. Pellagra is known to manifest in individuals deficient of niacin. What is the correlation of Isoniazid therapy and niacin deficiency? A. Isoniazid inhibits biological activation of niacin B. Isoniazid prevents absorption of niacin C. Isoniazid promotes excessive excretion of niacin D. Isoniazid inhibits endogenous synthesis of niacin E. Isoniazid acts a competitive inhibitor of niacin Answer- D- Isoniazid inhibits the...

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Case study- Pellagra- A 56–year-old male on Isoniazid therapy for tuberculosis …..

Niacin and Pellagra Basic concept Niacin (nicotinic acid and nicotinamide) is also known as vitamin B3. Both nicotinic acid and nicotinamide can serve as the dietary source of vitamin B3. Niacin is a pyridine carboxylic acid that is converted into an amide in the body. Niacin is not a true vitamin in the strictest definition since it can be derived from the amino acid tryptophan. However, the ability to utilize tryptophan for niacin synthesis is inefficient (60 mg of tryptophan are required to synthesize 1 mg of niacin). Also, synthesis of niacin from tryptophan requires vitamins B1, B2 and B6...

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Case study Malignant hyperthermia (Electron transport chain and oxidative phosphorylation)

Case details A 23-year-old college foot ball player sustains a compound fracture on the field. He is taken to surgery, during which the anesthesiologist notes a significantly increased body temperature (102 0 F). The operation is terminated without completion, as malignant hyperthermia is suspected. Which of the following components of ETC is likely to be responsible for this phenomenon? A. Complex I B. Complex II C. Complex III D. Complex IV E.  ATP synthase complex Answer- The right answer is- E- ATP Synthase complex. Patients with malignant hyperthermia experience uncoupling of oxidative phosphorylation . OXIDATIVE PHOSPHORYLATION Chemiosmosis- As the electrons...

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Case study- Malignant hyperthermia (Electron transport chain and oxidative phosphorylation)

Basic concept Electron Transport Chain The electron transport chain (ETC) is a series of membrane-bound electron carriers (Figure-1) Embedded in the mitochondrial inner membrane Electrons from NADH and FADH2 are transferred to complexes of the ETC Each complex transfers the electrons to the next complex in the chain. COMPLEXES OF ELECTRON TRANSPORT CHAIN Electrons flow through the respiratory chain through a redox span of 1.1 V from NAD+/NADH to O2/2H2O passing through three large protein complexes; NADH-Q oxidoreductase (Complex I), where electrons are transferred from NADH to coenzyme Q (Q) (also called ubiquinone); Q-cytochrome c oxidoreductase (Complex III), which passes...

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Case study- Enzyme Inhibition

A 54- year-old man complains of an acute onset of unilateral eye pain and reduction in the visual acuity. On physical examination, conjunctival injection (eye redness) and a mild-dilated and non reactive pupil is observed. Fundoscopic examination reveals cupping of the optic disc. Recognizing the signs and symptoms as glaucoma, the medication Acetazolamide is administered to decrease the production of aqueous fluid and lower the intraocular pressure. Acetazolamide is a non competitive inhibitor of carbonic anhydrase and therefore will cause: A. An increase in Km B. A decrease in Km C. An increase in Vmax D. A decrease in Vmax...

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Case study- Enzyme Inhibition- A 54-year-old man complains of an acute onset of unilateral eye pain and reduction in the visual acuity….

Basic concept Enzymes are catalysts of biological system. They speed up the rate of the reaction without themselves getting consumed during the process of catalysis. Active site is the place where the actual reaction between enzyme and substrate takes place. Coenzymes and cofactors are required by some of the enzymes to further accelerate the rate of enzyme catalyzed reaction. Many factors influence the rate of reaction including temperature, pH, substrate, enzyme and product concentration. Km denotes the affinity of the enzyme for its substrate, whereas Vmax signifies the maximum reaction velocity attained by enzyme catalyzed reaction. The enzyme activity can...

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Mucopolysaccharidoses- A case discussion

QUESTION  OF THE DAY A 6-year-old boy is seen by a pediatrician because his parents are concerned about his aggressive behavior, hyperactivity, and a loss of language skills. He also has recently become increasingly unsteady on his feet and has experienced a recent seizure. Slight facial feature coarsening is noted. In which of the following processes is this child most likely to have a disorder? A. Mobilization of glycogen B. Gluconeogenesis C. Salvage of purine bases D. Degradation of glycosaminoglycans E. Cholesterol metabolism ANSWER Answer- D- Degradation of Glycosaminoglycans Glycosaminoglycans are degraded by lysosomal hydrolases. A deficiency of one of the hydrolases results in Mucopolysaccharidoses. These are hereditary disorders in which...

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A 6 year-old boy who became aggressive

BASIC CONCEPT Please read the following text before attempting the question below. The carbohydrates are a group of naturally occurring carbonyl compounds (aldehydes or ketones) that also contain several hydroxyl groups. The carbohydrates include single sugars (monosaccharides) and their polymers, the oligosaccharides and polysaccharides. Glucose is the most important carbohydrate in mammalian system because nearly all carbohydrate in food is converted to glucose for metabolism. Sugars have large numbers of stereoisomers because they contain several asymmetric carbon atoms. The physiologically important monosaccharides include glucose, the “blood sugar,” and ribose, an important constituent of nucleotides and nucleic acids. The important disaccharides...

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