B.Pharm. Bachelor of Pharmacy Bachelor of Pharmacy (B.Pharm.) Biochemistry 2 — Questions and Answers
Question 1: Which coenzyme is required for the oxidative decarboxylation of pyruvate to acetyl-CoA?
- FAD
- NAD+
- Coenzyme A
- Thiamine pyrophosphate (Correct answer)
Correct answer: Thiamine pyrophosphate
Thiamine pyrophosphate (TPP) is the essential coenzyme for the pyruvate dehydrogenase complex that catalyzes decarboxylation of pyruvate.
Question 2: In the urea cycle, which amino acid donates both nitrogen atoms that appear in urea?
- Glutamine
- Aspartate and ammonia (Correct answer)
- Alanine
- Glutamate
Correct answer: Aspartate and ammonia
One nitrogen in urea comes from free ammonia (via carbamoyl phosphate) and the second comes from aspartate.
Question 3: Which enzyme is rate-limiting in cholesterol biosynthesis?
- Thiolase
- HMG-CoA synthase
- HMG-CoA reductase (Correct answer)
- Mevalonate kinase
Correct answer: HMG-CoA reductase
HMG-CoA reductase catalyzes the conversion of HMG-CoA to mevalonate and is the committed, rate-limiting step in cholesterol synthesis.
Question 4: The Cori cycle transfers energy from the liver to working muscles in what chemical form?
- Fatty acids
- Lactate
- Glucose (Correct answer)
- Ketone bodies
Correct answer: Glucose
The liver converts lactate (from muscles) back to glucose via gluconeogenesis and releases it into the blood for muscle use.
Question 5: Which type of RNA carries amino acids to the ribosome during translation?
- mRNA
- rRNA
- tRNA (Correct answer)
- snRNA
Correct answer: tRNA
Transfer RNA (tRNA) carries specific amino acids to the ribosome and matches them to codons on mRNA via its anticodon loop.
Question 6: Competitive inhibition of an enzyme increases the apparent Km but leaves Vmax unchanged. Which statement best explains this?
- The inhibitor permanently destroys active sites
- Excess substrate can displace the inhibitor from the active site (Correct answer)
- The inhibitor changes the enzyme's tertiary structure
- The inhibitor binds at an allosteric site
Correct answer: Excess substrate can displace the inhibitor from the active site
Competitive inhibitors bind reversibly to the active site; high substrate concentrations outcompete the inhibitor, restoring full Vmax.
Question 7: Which vitamin deficiency causes beriberi and is directly linked to impaired pyruvate dehydrogenase activity?
- Vitamin B2 (riboflavin)
- Vitamin B3 (niacin)
- Vitamin B1 (thiamine) (Correct answer)
- Vitamin B6 (pyridoxine)
Correct answer: Vitamin B1 (thiamine)
Thiamine (B1) is a precursor of TPP, the required cofactor for pyruvate dehydrogenase; its deficiency impairs aerobic glucose metabolism causing beriberi.
