Tagged: Namrata Chhabra

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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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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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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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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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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 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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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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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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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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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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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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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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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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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- 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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‘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 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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