Category: Chemistry of Biomolecules

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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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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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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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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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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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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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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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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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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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