B.Pharm. Bachelor of Pharmacy Bachelor of Pharmacy (B.Pharm.) Biochemistry 3 — Questions and Answers
Question 1: Which bond links nucleotides together in a DNA strand?
- Hydrogen bond
- Peptide bond
- Phosphodiester bond (Correct answer)
- Glycosidic bond
Correct answer: Phosphodiester bond
Phosphodiester bonds connect the 3'-OH of one deoxyribose to the 5'-phosphate of the next nucleotide, forming the DNA backbone.
Question 2: During fatty acid synthesis, malonyl-CoA is formed by carboxylation of acetyl-CoA. Which cofactor is essential for this reaction?
- Biotin (Correct answer)
- Lipoic acid
- Coenzyme A
- Pyridoxal phosphate
Correct answer: Biotin
Acetyl-CoA carboxylase requires biotin as a CO2 carrier to carboxylate acetyl-CoA to malonyl-CoA in the committed step of fatty acid synthesis.
Question 3: The Km value of an enzyme for its substrate reflects:
- The maximum reaction rate achievable
- The substrate concentration at which reaction rate is half of Vmax (Correct answer)
- The dissociation constant of the enzyme-product complex
- The total enzyme concentration in the reaction
Correct answer: The substrate concentration at which reaction rate is half of Vmax
By definition, Km is the substrate concentration ([S]) at which the reaction velocity equals Vmax/2, indicating enzyme-substrate affinity.
Question 4: Which purine base pairs with thymine in DNA?
- Guanine
- Cytosine
- Uracil
- Adenine (Correct answer)
Correct answer: Adenine
Adenine pairs with thymine via two hydrogen bonds in the Watson-Crick model of DNA base pairing.
Question 5: What is the net ATP yield from complete oxidation of one molecule of palmitate (16-carbon saturated fatty acid)?
- 106 ATP
- 129 ATP (Correct answer)
- 38 ATP
- 80 ATP
Correct answer: 129 ATP
Oxidation of palmitoyl-CoA yields 7 FADH2, 7 NADH, 8 acetyl-CoA; total accounting gives approximately 129 ATP equivalents.
Question 6: Sickle cell anemia results from a point mutation causing which amino acid substitution in hemoglobin?
- Valine replaces glutamic acid at position 6 of the beta chain (Correct answer)
- Glutamic acid replaces valine at position 6 of the alpha chain
- Lysine replaces glutamine at position 6 of the beta chain
- Proline replaces leucine at position 1 of the beta chain
Correct answer: Valine replaces glutamic acid at position 6 of the beta chain
A GAG→GTG mutation converts glutamic acid to valine at position 6 of the β-globin chain, causing HbS polymerization under low oxygen.
Question 7: Which enzyme catalyzes the first committed step of glycolysis?
- Aldolase
- Phosphoglucose isomerase
- Hexokinase
- Phosphofructokinase-1 (Correct answer)
Correct answer: Phosphofructokinase-1
Phosphofructokinase-1 (PFK-1) converts fructose-6-phosphate to fructose-1,6-bisphosphate and is the key regulatory, committed step of glycolysis.
B.Pharm. Bachelor of Pharmacy Bachelor of Pharmacy (B.Pharm.) Biochemistry 3
Which bond links nucleotides together in a DNA strand?