B.Pharm. Bachelor of Pharmacy Bachelor of Pharmacy (B.Pharm.) Biochemistry 4 — Questions and Answers
Question 1: In oxidative phosphorylation, the proton gradient across the inner mitochondrial membrane drives ATP synthesis via which complex?
- Complex I
- Complex III
- Complex IV
- Complex V (ATP synthase) (Correct answer)
Correct answer: Complex V (ATP synthase)
Complex V (ATP synthase/F0F1-ATPase) harnesses the proton-motive force to phosphorylate ADP to ATP through rotary catalysis.
Question 2: Transamination reactions require which coenzyme derived from vitamin B6?
- Pyridoxal phosphate (PLP) (Correct answer)
- Thiamine pyrophosphate (TPP)
- Nicotinamide adenine dinucleotide (NAD+)
- Flavin adenine dinucleotide (FAD)
Correct answer: Pyridoxal phosphate (PLP)
Pyridoxal phosphate forms a Schiff base with the amino acid substrate and shuttles the amino group between donors and α-ketoglutarate in transamination.
Question 3: Which metabolic pathway is exclusively located in the cytosol of eukaryotic cells?
- Citric acid cycle
- Beta-oxidation of fatty acids
- Glycolysis (Correct answer)
- Oxidative phosphorylation
Correct answer: Glycolysis
All ten enzymatic steps of glycolysis occur in the cytoplasm; the other pathways listed are mitochondrial.
Question 4: What is the role of feedback inhibition by CTP on aspartate transcarbamoylase (ATCase) in pyrimidine biosynthesis?
- It activates ATCase to produce more pyrimidines
- It inhibits ATCase to prevent overproduction of pyrimidines (Correct answer)
- It degrades excess uracil in the cell
- It stimulates purine biosynthesis instead
Correct answer: It inhibits ATCase to prevent overproduction of pyrimidines
CTP, the end product of pyrimidine synthesis, allosterically inhibits ATCase at the regulatory subunit, providing classic feedback regulation.
Question 5: Which lipoprotein is primarily responsible for transporting dietary triglycerides from the intestine to peripheral tissues?
- LDL
- HDL
- VLDL
- Chylomicrons (Correct answer)
Correct answer: Chylomicrons
Chylomicrons are assembled in intestinal enterocytes and transport exogenous dietary triglycerides via lymph into the bloodstream to peripheral tissues.
Question 6: Which enzyme unwinds the DNA double helix ahead of the replication fork?
- DNA polymerase III
- DNA ligase
- DNA helicase (Correct answer)
- Primase
Correct answer: DNA helicase
DNA helicase uses ATP hydrolysis to break hydrogen bonds between base pairs and separate the two DNA strands at the replication fork.
Question 7: The pentose phosphate pathway primarily produces which two products used in biosynthesis?
- ATP and FADH2
- NADPH and ribose-5-phosphate (Correct answer)
- Acetyl-CoA and OAA
- Pyruvate and lactate
Correct answer: NADPH and ribose-5-phosphate
The oxidative branch of the pentose phosphate pathway generates NADPH (for reductive biosynthesis and antioxidant defense) and ribose-5-phosphate (for nucleotide synthesis).
B.Pharm. Bachelor of Pharmacy Bachelor of Pharmacy (B.Pharm.) Biochemistry 4
In oxidative phosphorylation, the proton gradient across the inner mitochondrial membrane drives ATP synthesis via which complex?