Answer- Vitamin C is required for the synthesis of carnitine. Carnitine ( β hydroxy-γ-trimethyl ammonium butyrate), (CH3)3N+—CH2—CH(OH)—CH2—COO–, is widely distributed and is particularly abundant in muscle. Carnitine facilitates the beta-oxidation of fatty acids, through its role in transporting long chain fatty acids from the cytoplasm into the mitochondrial matrix of cardiac and skeletal muscle. Vitamin C dependent trimethyllysine and -γ butyrobetaine hydroxylases are required for the synthesis of carnitine. Vitamin C acts as a reducing agent in these reactions.
Q.2- Why is it said that Niacin and vitamin D are not true vitamins?
Answer- The distinguishing feature of the vitamins is that they generally cannot be synthesized by mammalian cells and, therefore, must be supplied in the diet.Vitamin D, which is formed in the skin after exposure to sunlight, and niacin, which can be formed from the essential amino acid tryptophan, do not strictly comply with this definition. However, the ability to utilize tryptophan for niacin synthesis is inefficient (60 mg of tryptophan are required to synthesize 1 mg of niacin).
Q.3- What is the cause of bleeding tendencies in obstructive jaundice?
Answer- In obstructive jaundice there is obstruction to the outflow of bile. Bile salts are needed for the absorption of fat soluble vitamins. Vitamin K, a fat soluble vitamin has an active role in coagulation of blood. In conditions of malabsorption or obstructive jaundice, Vitamin K deficiency sets in with the resultant impaired coagulation of blood and bleeding tendencies.
Q.4- Which form of vitamin B2 (Riboflavin) is required for the activity of succinate dehydrogenase enzyme of TCA cycle ?
Answer- Succinate dehydrogenase catalyzes the conversion of succinate to fumarate; FAD form of vitamin B2 is required as a coenzyme for this reaction.
Q.5- Which vitamin is required for the activity of muscle glycogen phosphorylase enzyme?
Answer- B6-P is required for the activity of muscle glycogen phosphorylase enzyme. Approximately 80% of the body’s total vitamin B6 is present in muscle, mostly associated with glycogen phosphorylase. This is not available in deficiency, but is released in starvation, when glycogen reserves become depleted, and is then available, especially in liver and kidney, to meet increased requirement for gluconeogenesis from amino acids.
Q.6- Which vitamin is required in higher amount with increasing carbohydrate load?
Answer- The requirement of thiamine increases with heavy carbohydrate diet. Because thiamine is required for enzymes involved in glucose metabolism such as Pyruvate dehydrogenase complex, Alpha keto glutarate dehydrogenase complex and transketolase, so its requirement also increases with the increasing carbohydrate load for the proper functioning of these enzymes. The severe thiamine deficiency disease known as Beriberi is the result of a diet that is carbohydrate rich and thiamine deficient. In subjects on a relatively high carbohydrate diet, this results in increased plasma concentrations of lactate and pyruvate which may cause life-threatening lactic acidosis.
Q.7- Which vitamin is required for the synthesis of Sphingol required for the formation of sphingomyelin?
Answer- Vitamin B6-P is required for the formation of Sphingol (an amino alcohol) required for the synthesis of sphingomyelins (Sphingophospholipids).
Q.8- Name a vitamin required for as a coenzyme for the activity of SGOT?
Answer- SGOT- Serum Glutamate Oxalo acetate transaminase is B6-P dependent and catalyzes the reversible transamination reaction involving glutamate and oxaloacetate for the formation of aspartate and alpha ketoglutarate.
Q.9-Name a vitamin required for the activity of dihydrofolate reductase?
Answer- Dihydrofolate reductase as the name indicates is associated with folic acid and catalyzes the conversion of dihydrofolate to Tetrahydrofolate (active form). Methotrexate acts as a competitive inhibitor of this enzyme and is used as an anticancer drug.
Q.10- Name a vitamin, the deficiency of which is detected by Reduced Red cell Glutathione reductase activity.
Answer- The deficiency of vitamin B2 is detected by estimating RBC Glutathione reductase enzyme.
Q.11- What should be the clinical outcome if Riboflavin deficiency is detected?
Answer- Most prominent effects are seen on the skin, mucosa and eyes: Glossitis (magenta tongue, geographical tongue), cheilosis, angular stomatitis (fissures at the corners of the mouth), sore throat, burning of the lips, mouth, and tongue ,inflamed mucous membranes, pruritus (itching) and seborrheic dermatitis (moist scaly skin inflammation) are the symptoms commonly observed in deficient individuals.
Q.12- Name a vitamin/ Vitamins required for the activity of Pyruvate dehydrogenase complex.
Answer- Pyruvate dehydrogenase, a multienzyme complex, catalyzes the oxidative decarboxylation of pyruvate to form Acetyl co A. It requires Thiamine pyrophosphate (TPP), pantothenic acid, lipoic acid, riboflavin and niacin for it’s activity. The deficiency of any of these vitamins can affect the activity of this enzyme complex. Most common out of these is thiamine deficiency.
Q.13- Name the vitamin that is required as a coenzyme for the conversion of Acetyl co A to Malonyl co A?
Answer- The conversion of Acetyl co A to malonyl co A , the first step of fatty acid synthesis, is catalyzed by Acetyl co A carboxylase enzyme, that requires biotin as a cofactor. It is a carboxylation reaction.
Q.14- Which enzyme is inhibited by Dicoumarol and what is the mode of inhibition?
Answer- Dicoumarol acts as an anti coagulant. It is a competitive inhibitor of Epoxide reductase, the enzyme that catalyzes the conversion of epoxide form of vitamin K to quinone form. Quinone form is further reduced to hydroquinone form (functional form) that can be further utilized for gamma carboxylation of glutamic acid residues. In the presence of dicoumarol, the functional form of vitamin K is not regenerated and hence coagulation cascade is not triggered.
Q.15- Which vitamin/vitamins participate in the synthesis of catecholamines?
Answer- Vitamin C and B6 are required for the synthesis of catecholamines. B6 is required for the decarboxylation and vitamin C is required for the hydroxylation reactions.
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