ADVANCED BIOCHEMISTRY 210 EXAM
QUESTIONS AND ANSWERS
1. A buffer is prepared by mixing 500 mL of 0.2 M acetic acid (pKa = 4.76) and 500 mL of 0.1 M
sodium acetate. What is the final pH of this buffer?
A. 4.76
B. 4.46
C. 5.06
D. 4.16
Answer: B
Conceptual Explanation: Using the Henderson-Hasselbalch equation: pH = pKa + log([A-
]/[HA]). Here, [A-] = 0.05 mol and [HA] = 0.1 mol in 1L. pH = 4.76 + log(0.05/0.1) = 4.76 +
log(0.5) = 4.76 - 0.301 = 4.459.
2. Which amino acid possesses a side chain with a pKa value closest to physiological pH (7.4),
allowing it to act as both a proton donor and acceptor in enzyme catalysis?
A. Lysine
B. Histidine
C. Arginine
,D. Cysteine
Answer: B
Conceptual Explanation: The imidazole side chain of Histidine has a pKa of approximately
6.0, which is close to physiological pH, making it highly versatile in acid-base catalysis.
3. In the Ramachandran plot, which region corresponds to the conformation of a right-
handed alpha-helix?
A. Bottom-left quadrant
B. Top-right quadrant
C. Top-left quadrant
D. Bottom-right quadrant
Answer: A
Conceptual Explanation: Right-handed alpha-helices have phi angles around -57 and psi
angles around -47, placing them in the bottom-left quadrant of the plot.
4. During the formation of a peptide bond, what is the nature of the reaction and the primary
geometry of the resulting C-N bond?
A. Hydrolysis; free rotation
B. Condensation; partial double-bond character
C. Oxidation; tetrahedral geometry
D. Reduction; triple-bond character
, Answer: B
Conceptual Explanation: Peptide bond formation is a condensation reaction. Due to
resonance, the C-N bond has partial double-bond character, which restricts rotation and
keeps the bond planar.
5. Which of the following thermodynamics statements is true regarding protein folding?
A. The change in enthalpy (dH) is the primary driving force.
B. The overall change in Gibbs free energy (dG) for folding is usually highly positive.
C. Folding is driven by the hydrophobic effect, which increases the entropy of water
molecules.
D. Folding decreases the total entropy of the universe.
Answer: C
Conceptual Explanation: The ‘hydrophobic effect’ is driven by an increase in the entropy
of the surrounding solvent (water) as non-polar residues sequester into the protein core,
releasing ordered water cages.
6. An enzyme follows Michaelis-Menten kinetics. If the substrate concentration [S] is equal to
3 times the Km, what is the initial velocity (v0) as a fraction of Vmax?
A. 0.25 Vmax
B. 0.75 Vmax
C. 0.50 Vmax
QUESTIONS AND ANSWERS
1. A buffer is prepared by mixing 500 mL of 0.2 M acetic acid (pKa = 4.76) and 500 mL of 0.1 M
sodium acetate. What is the final pH of this buffer?
A. 4.76
B. 4.46
C. 5.06
D. 4.16
Answer: B
Conceptual Explanation: Using the Henderson-Hasselbalch equation: pH = pKa + log([A-
]/[HA]). Here, [A-] = 0.05 mol and [HA] = 0.1 mol in 1L. pH = 4.76 + log(0.05/0.1) = 4.76 +
log(0.5) = 4.76 - 0.301 = 4.459.
2. Which amino acid possesses a side chain with a pKa value closest to physiological pH (7.4),
allowing it to act as both a proton donor and acceptor in enzyme catalysis?
A. Lysine
B. Histidine
C. Arginine
,D. Cysteine
Answer: B
Conceptual Explanation: The imidazole side chain of Histidine has a pKa of approximately
6.0, which is close to physiological pH, making it highly versatile in acid-base catalysis.
3. In the Ramachandran plot, which region corresponds to the conformation of a right-
handed alpha-helix?
A. Bottom-left quadrant
B. Top-right quadrant
C. Top-left quadrant
D. Bottom-right quadrant
Answer: A
Conceptual Explanation: Right-handed alpha-helices have phi angles around -57 and psi
angles around -47, placing them in the bottom-left quadrant of the plot.
4. During the formation of a peptide bond, what is the nature of the reaction and the primary
geometry of the resulting C-N bond?
A. Hydrolysis; free rotation
B. Condensation; partial double-bond character
C. Oxidation; tetrahedral geometry
D. Reduction; triple-bond character
, Answer: B
Conceptual Explanation: Peptide bond formation is a condensation reaction. Due to
resonance, the C-N bond has partial double-bond character, which restricts rotation and
keeps the bond planar.
5. Which of the following thermodynamics statements is true regarding protein folding?
A. The change in enthalpy (dH) is the primary driving force.
B. The overall change in Gibbs free energy (dG) for folding is usually highly positive.
C. Folding is driven by the hydrophobic effect, which increases the entropy of water
molecules.
D. Folding decreases the total entropy of the universe.
Answer: C
Conceptual Explanation: The ‘hydrophobic effect’ is driven by an increase in the entropy
of the surrounding solvent (water) as non-polar residues sequester into the protein core,
releasing ordered water cages.
6. An enzyme follows Michaelis-Menten kinetics. If the substrate concentration [S] is equal to
3 times the Km, what is the initial velocity (v0) as a fraction of Vmax?
A. 0.25 Vmax
B. 0.75 Vmax
C. 0.50 Vmax
