BIOCHEM 210 FINAL EXAMINATION
QUESTIONS AND ANSWERS
1. Which of the following conditions would lead to the most effective buffering by a weak
acid with a pKa of 4.76?
A. pH 2.76
B. pH 4.76
C. pH 6.76
D. pH 7.00
Answer: B
Conceptual Explanation: The maximum buffering capacity of a weak acid occurs when the
pH is equal to its pKa, as the concentrations of the acid and its conjugate base are equal.
2. Which amino acid contains a secondary amino group and often acts as a helix breaker in
protein structures?
A. Glycine
B. Alanine
C. Histidine
D. Proline
,Answer: D
Conceptual Explanation: Proline has a cyclic structure that creates a secondary amine
(imino acid) and lacks a hydrogen on its nitrogen when in a peptide bond, preventing it
from participating in the hydrogen-bonding pattern of an alpha helix.
3. In the Ramachandran plot, what do the Phi and Psi angles represent?
A. Bond angles within the R-group
B. Torsion angles around the C-alpha-N and C-alpha-C bonds
C. The angle of the hydrogen bond in beta-sheets
D. The rotation of the peptide bond itself
Answer: B
Conceptual Explanation: Phi is the rotation angle around the N-C-alpha bond, and Psi is
the rotation angle around the C-alpha-C bond. These angles define the secondary structure
of the polypeptide backbone.
4. Hemoglobin’s affinity for oxygen decreases as the concentration of 2,3-
bisphosphoglycerate (2,3-BPG) increases. What is the mechanism?
A. 2,3-BPG binds to the iron in heme
B. 2,3-BPG competes with oxygen for the same binding site
C. 2,3-BPG oxidizes Fe2+ to Fe3+
D. 2,3-BPG stabilizes the T-state (tense) by binding to the central cavity
, Answer: D
Conceptual Explanation: 2,3-BPG is a negative heterotropic effector that binds to the
central cavity of the hemoglobin tetramer, stabilizing the low-affinity T-state and
promoting oxygen release to tissues.
5. According to the Michaelis-Menten model, what does the Km (Michaelis constant)
represent?
A. The maximum velocity of the reaction
B. The substrate concentration at which the reaction rate is half of Vmax
C. The concentration of enzyme required to reach Vmax
D. The turnover number of the enzyme
Answer: B
Conceptual Explanation: Km is defined as the substrate concentration [S] at which the
initial velocity is exactly half of the maximum velocity (Vmax). It is often used as a measure
of an enzyme’s affinity for its substrate.
6. How does a competitive inhibitor affect the Lineweaver-Burk plot of an enzyme?
A. The Y-intercept stays the same, the slope increases
B. The Y-intercept increases, X-intercept stays the same
C. Both intercepts change and the lines are parallel
D. The Y-intercept decreases, the X-intercept increases
QUESTIONS AND ANSWERS
1. Which of the following conditions would lead to the most effective buffering by a weak
acid with a pKa of 4.76?
A. pH 2.76
B. pH 4.76
C. pH 6.76
D. pH 7.00
Answer: B
Conceptual Explanation: The maximum buffering capacity of a weak acid occurs when the
pH is equal to its pKa, as the concentrations of the acid and its conjugate base are equal.
2. Which amino acid contains a secondary amino group and often acts as a helix breaker in
protein structures?
A. Glycine
B. Alanine
C. Histidine
D. Proline
,Answer: D
Conceptual Explanation: Proline has a cyclic structure that creates a secondary amine
(imino acid) and lacks a hydrogen on its nitrogen when in a peptide bond, preventing it
from participating in the hydrogen-bonding pattern of an alpha helix.
3. In the Ramachandran plot, what do the Phi and Psi angles represent?
A. Bond angles within the R-group
B. Torsion angles around the C-alpha-N and C-alpha-C bonds
C. The angle of the hydrogen bond in beta-sheets
D. The rotation of the peptide bond itself
Answer: B
Conceptual Explanation: Phi is the rotation angle around the N-C-alpha bond, and Psi is
the rotation angle around the C-alpha-C bond. These angles define the secondary structure
of the polypeptide backbone.
4. Hemoglobin’s affinity for oxygen decreases as the concentration of 2,3-
bisphosphoglycerate (2,3-BPG) increases. What is the mechanism?
A. 2,3-BPG binds to the iron in heme
B. 2,3-BPG competes with oxygen for the same binding site
C. 2,3-BPG oxidizes Fe2+ to Fe3+
D. 2,3-BPG stabilizes the T-state (tense) by binding to the central cavity
, Answer: D
Conceptual Explanation: 2,3-BPG is a negative heterotropic effector that binds to the
central cavity of the hemoglobin tetramer, stabilizing the low-affinity T-state and
promoting oxygen release to tissues.
5. According to the Michaelis-Menten model, what does the Km (Michaelis constant)
represent?
A. The maximum velocity of the reaction
B. The substrate concentration at which the reaction rate is half of Vmax
C. The concentration of enzyme required to reach Vmax
D. The turnover number of the enzyme
Answer: B
Conceptual Explanation: Km is defined as the substrate concentration [S] at which the
initial velocity is exactly half of the maximum velocity (Vmax). It is often used as a measure
of an enzyme’s affinity for its substrate.
6. How does a competitive inhibitor affect the Lineweaver-Burk plot of an enzyme?
A. The Y-intercept stays the same, the slope increases
B. The Y-intercept increases, X-intercept stays the same
C. Both intercepts change and the lines are parallel
D. The Y-intercept decreases, the X-intercept increases
