Amino Acid: Metabolism MCQs

Based on metabolism, amino acids can be classified into - Ketogenic - These amino acids yield only acetyl CoA on oxidation which cannot be used for gluconeogenesis. Ex: Lysine and leucine Ketogenic and glucogenic - Yield both acetyl CoA and intermediates that can be used for gluconeogenesis. Ex: Phenylalanine, tyrosine, tryptophan, and isoleucine Glucogenic - These amino acids yield only pyruvate, or four- and five-carbon intermediates of the citric acid cycle, which can be used for gluconeogenesis. Ex: All the remaining amino acids Reference: Harper's 32nd edition, page 146

Ans. A. 20% Cephalic phase accounts for 20% of gastric acid secretion and gastric phase accounts 70-80% of gastric acid secretion.

Ans. is 'd' i.e., Nicotinic acid [Ref: Harper's 28th /e p. 266, 268, 254] Tyrosine is a precursor of many important compounds such as catecholamines (epinephrineQ, norepinephrine Q),dopamine), thyroxineQ, triiodothryonine, melanin0.

Ans. is `c' i.e., Temperature inversion A temperature inversion is a thin layer of the atmosphere where the normal decrease in temperature with height swithees to the temperature increasing with height. An inversion can lead to pollution such as smog being trapped close to the grand (lower layers of atmosphere). Temperature inversion may occur during the passage of a cold front or result from the invasion of sea air by a cooler onshore breeze. o Overnight radiative cooling of surface air often results in a nocturnal temperature inversion that is dissipated after sunrise by the warming of air near the ground.

Ans. is 'd' i.e., Mitochondria of Hepatocytes [Ref : Harper 29'/e p. 274] Deamination means removal of amino group of amino acid in the form of ammonia. Thus, an amino acid is converted to a keto acid. Deamination coupled with oxidation is called oxidative deamination. It occurs in the mitochondria. Oxidative deamination occurs primarily in the liver (major organ) and kidney.

Methionine is an essential amino acid, so it cannot be synthesized from Cysteine. Sulfur of cysteine is donated by sulfur of methionine. This is called trans-sulfuration reaction. PLP is the coenzyme of transsulfuration. The reaction is catalyzed by Cystathionine beta Synthase and Cystathionase enzyme. Reference: Harper's 32 nd edition, page 284,285

In the reaction HA → H+ + A– , the conjugate acid and conjugate base The Henderson-Hasselbalch equation describes the behaviour of Weak Acids & Buffers The Henderson-Hasselbalch equation is derived below. A weak acid, HA, ionizes as follows: HA ←→ H+ + A-, A-, is conjugate base & HA is conjugate acid, H + is hydrogen ion So Option B is correct Reference: Harper's illustrated biochemistry 32nd edition CH 2 PN 11

Urinary metabolite in Vitamin B 6 deficiency: Xanthurenic acid Urinary Metabolite in Folic Acid Deficiency: Formimino Glutamic acid, Homocystine Urinary metabolite in Vitamin B 12 deficiency: Homocystine, Methyl Malonic Acid 5-HIAA is elevated in carcinoid syndrome Tryptophan metabolism - Tryptophan is degraded to amphibolic intermediates via the kynurenine-anthranilate pathway. Tryptophan 2,3-dioxygenase opens the indole ring, incorporates molecular oxygen, and forms N-formylkynurenine. Hydrolytic removal of the formyl group of N-formylkynurenine, catalyzed by kynurenine formylase, produces kynurenine. Since kynureninase requires pyridoxal phosphate , excretion of xanthurenate in response to a tryptophan load is diagnostic of vitamin B6 deficiency. Reference: Harper's 32nd edition, page 306,308