Q1. Which is an example of a 'mechanism-based inhibitor' of an enzyme? (C) Allopurinol - It is a classic suicide/mechanism-based inhibitor of xanthine oxidase; the enzyme converts it to alloxanthine, which remains tightly bound and inactivates the enzyme.

Q2. Correct order of electron flow in the ETC: (A) Complex I → Coenzyme Q → Complex III → Complex IV - Electrons from NADH enter Complex I, are shuttled by the mobile carrier CoQ to Complex III, then (via cytochrome c) to Complex IV, and finally to ATP synthase. Option A is the only sequence with no incorrect step (CoQ correctly placed between Complex I and III).

Q3. Absorbed dietary lipids are transported as: (B) Chylomicrons - Dietary (exogenous) lipids absorbed in the intestine are packaged into chylomicrons for transport via lymph into the bloodstream (VLDL carries endogenous lipids from the liver; mixed micelles are the intraluminal form before absorption).

Q4. Arachidonic acid is: (A) An omega-6 fatty acid containing 20 carbons and four double bonds - (Option B is incorrect because linoleic acid is an omega-6, not omega-3, fatty acid.)

Q5. Net ATP yield from beta-oxidation of palmitic acid (C16): (D) 106 ATP - 7 cycles give 7 FADH2 (1.5 ATP each) + 7 NADH (2.5 ATP each); 8 acetyl-CoA through TCA give 10 ATP each = 80+10.5+17.5 = 108 gross ATP, minus 2 ATP used for fatty acid activation = 106 net ATP.

Q6. Vitamins involved in carboxylation reactions: (C) Vitamin K and biotin - Biotin is the cofactor for carboxylases (e.g., pyruvate carboxylase); vitamin K is required for gamma-carboxylation of clotting factors (II, VII, IX, X).

Q7. Both Wernicke's disease and beriberi are treated with: (A) Thiamine - Both are classic manifestations of thiamine (vitamin B1) deficiency.

Q8. Alpha-tocopherol prevents rancidity by virtue of being: (A) Antioxidant - Vitamin E scavenges free radicals/reactive oxygen species, preventing lipid peroxidation (rancidity) of polyunsaturated fatty acids.

Q9. Vitamin that may mask anemia due to vitamin B12 deficiency: (A) Folic acid - High-dose folate can correct the megaloblastic/hematologic picture of B12 deficiency while the underlying neurological damage silently progresses - hence it "masks" the diagnosis.

Q10. Rennin acts on casein of milk in infants in the presence of: (D) Ca⁺⁺ - Rennin (chymosin) converts soluble casein to insoluble paracasein, which requires calcium ions to form the curd (calcium paracaseinate).

Q11. Marker enzyme for peroxisomes: (B) Catalase - Catalase is the classic peroxisomal marker enzyme, used to break down H2O2 generated during peroxisomal beta-oxidation and other oxidase reactions.

Quick answer key: 1-C, 2-A, 3-B, 4-A, 5-D, 6-C, 7-A, 8-A, 9-A, 10-D, 11-B

These align with the standard biochemistry references (Harper's Illustrated Biochemistry; Basic Medical Biochemistry - A Clinical Approach, 6e) and match the pen-marked answers visible on your paper for Q5-Q9.

Q12. Cellular oxidant species are: (D) Oxygen containing free radicals and highly reactive species containing oxygen or both oxygen and nitrogen - this is the most complete definition, covering both reactive oxygen species (ROS) and reactive nitrogen species (RNS).

Q13. Homopolysaccharide made of fructose: (C) Inulin - Inulin is a fructose homopolysaccharide (a fructan) found in tubers like dahlia and Jerusalem artichoke, used clinically to measure GFR. Cellulose and starch are both glucose homopolysaccharides.

Q14. Hallmark of untreated type 1 diabetes mellitus: (C) Hyperglycemia and ketoacidosis - Absolute insulin deficiency in T1DM drives unrestrained lipolysis and ketogenesis, causing diabetic ketoacidosis. (Hyperglycemic hyperosmolar state is characteristic of T2DM.)

Q15. Phenylalanine enters the TCA cycle at: (C) Fumarate - Phenylalanine → tyrosine → ... is degraded to fumarate and acetoacetate (→ acetyl-CoA), making it both glucogenic and ketogenic; it enters the TCA cycle as fumarate.

Q16. Milk protein (casein) in the infant stomach is digested by: (D) Rennin - Rennin (chymosin) is the milk-clotting enzyme active in infant gastric mucosa, converting caseinogen to insoluble casein (paracasein) for digestion by pepsin.

Q17. Amino acid required for heme synthesis: (C) Glycine - Glycine condenses with succinyl-CoA (catalyzed by ALA synthase) to form delta-aminolevulinic acid (ALA), the first step of heme synthesis.

Q18. Equation commonly used to estimate GFR from serum creatinine, age, sex, and race: (D) CKD-EPI equation - The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation, incorporating age, sex, and race with serum creatinine, is now the preferred/most commonly used method (more accurate than MDRD, especially at higher GFR); Schwartz equation is for pediatric patients.

Q19. Associated with ping-pong mechanism: (B) Facilitated diffusion - The "ping-pong" model describes carrier proteins (e.g., GLUT transporters) alternating between two conformational states ("ping" exposed outward, "pong" exposed inward) to move solute across the membrane - this is the classic model for facilitated diffusion (Harper's Illustrated Biochemistry).

Q20. Hormone primarily responsible for regulating appetite and energy balance: (B) Leptin - Secreted by adipocytes in proportion to fat mass, leptin acts on the hypothalamus to suppress appetite and increase energy expenditure, serving as the principal long-term regulator of energy balance.

Quick answer key (Q12-Q20): 12-D, 13-C, 14-C, 15-C, 16-D, 17-C, 18-D, 19-B, 20-B

Note on Q19: your paper has (C) Active transport pen-marked, but per Harper's Illustrated Biochemistry the ping-pong carrier model specifically describes facilitated diffusion (uniporter mechanism), not active transport - worth double-checking with your course material/answer key if this was explicitly taught differently in your lectures.