BCH 4053 Exam 2 V1 | BCH 4053
Biochemistry I | Actual Q&A with
Rationale (BCH4053 Exam 2) | University
of Central Florida
1. Which of the following describes the effect of 2,3-bisphosphoglycerate (2,3-BPG) on
hemoglobin?
A. It increases the affinity of hemoglobin for oxygen by stabilizing the R-state.
B. It decreases oxygen affinity by stabilizing the T-state, facilitating oxygen release in
tissues.
C. It binds to the iron atom in the heme group to prevent carbon monoxide poisoning.
D. It acts as a competitive inhibitor for oxygen at the heme binding site.
Answer: B
Rationale: 2,3-BPG is a heterotropic allosteric effector that binds to the central cavity of
the hemoglobin tetramer. By binding to the T-state (deoxy-hemoglobin), it stabilizes this
low-affinity conformation and shifts the equilibrium away from the R-state. This
mechanism is essential for the efficient delivery of oxygen to peripheral tissues where
oxygen tension is low.
2. In the Michaelis-Menten model, what does the constant Km represent?
A. The maximum velocity of the reaction when the enzyme is saturated.
,B. The substrate concentration at which the reaction velocity is half of Vmax.
C. The number of substrate molecules converted to product per unit time.
D. The equilibrium constant for the dissociation of the product from the enzyme.
Answer: B
Rationale: Km, the Michaelis constant, is defined as the substrate concentration required
for an enzyme to reach one-half of its maximum velocity. It provides an inverse measure of
the enzyme’s affinity for its substrate, with a low Km indicating high affinity. This value is
characteristic for a specific enzyme-substrate pair under defined conditions of temperature
and pH.
3. Which type of inhibition can be overcome by increasing the substrate concentration?
A. Competitive inhibition
B. Uncompetitive inhibition
C. Non-competitive inhibition
D. Mixed inhibition
Answer: A
Rationale: Competitive inhibitors resemble the substrate and compete for binding at the
active site of the enzyme. Because the inhibitor and substrate compete for the same site,
adding excess substrate eventually outcompetes the inhibitor. Consequently, the Vmax of
the reaction remains unchanged, even though the apparent Km increases.
, 4. What is the characteristic appearance of a Lineweaver-Burk plot for uncompetitive
inhibition compared to no inhibitor?
A. The lines intersect at the y-axis.
B. The lines intersect at the x-axis.
C. The lines intersect in the second quadrant.
D. The lines are parallel to each other.
Answer: D
Rationale: Uncompetitive inhibitors bind only to the enzyme-substrate (ES) complex, not
the free enzyme. This binding reduces both the apparent Vmax and the apparent Km by the
same factor, resulting in a shift of both intercepts on a double-reciprocal plot. Because the
ratio of the slopes remains constant, the resulting lines for inhibited and uninhibited
reactions are parallel.
5. Which amino acids constitute the catalytic triad found in serine proteases like
chymotrypsin?
A. Aspartate, Histidine, and Serine
B. Serine, Histidine, and Lysine
C. Cysteine, Histidine, and Aspartate
D. Serine, Glutamate, and Histidine
Answer: A
Biochemistry I | Actual Q&A with
Rationale (BCH4053 Exam 2) | University
of Central Florida
1. Which of the following describes the effect of 2,3-bisphosphoglycerate (2,3-BPG) on
hemoglobin?
A. It increases the affinity of hemoglobin for oxygen by stabilizing the R-state.
B. It decreases oxygen affinity by stabilizing the T-state, facilitating oxygen release in
tissues.
C. It binds to the iron atom in the heme group to prevent carbon monoxide poisoning.
D. It acts as a competitive inhibitor for oxygen at the heme binding site.
Answer: B
Rationale: 2,3-BPG is a heterotropic allosteric effector that binds to the central cavity of
the hemoglobin tetramer. By binding to the T-state (deoxy-hemoglobin), it stabilizes this
low-affinity conformation and shifts the equilibrium away from the R-state. This
mechanism is essential for the efficient delivery of oxygen to peripheral tissues where
oxygen tension is low.
2. In the Michaelis-Menten model, what does the constant Km represent?
A. The maximum velocity of the reaction when the enzyme is saturated.
,B. The substrate concentration at which the reaction velocity is half of Vmax.
C. The number of substrate molecules converted to product per unit time.
D. The equilibrium constant for the dissociation of the product from the enzyme.
Answer: B
Rationale: Km, the Michaelis constant, is defined as the substrate concentration required
for an enzyme to reach one-half of its maximum velocity. It provides an inverse measure of
the enzyme’s affinity for its substrate, with a low Km indicating high affinity. This value is
characteristic for a specific enzyme-substrate pair under defined conditions of temperature
and pH.
3. Which type of inhibition can be overcome by increasing the substrate concentration?
A. Competitive inhibition
B. Uncompetitive inhibition
C. Non-competitive inhibition
D. Mixed inhibition
Answer: A
Rationale: Competitive inhibitors resemble the substrate and compete for binding at the
active site of the enzyme. Because the inhibitor and substrate compete for the same site,
adding excess substrate eventually outcompetes the inhibitor. Consequently, the Vmax of
the reaction remains unchanged, even though the apparent Km increases.
, 4. What is the characteristic appearance of a Lineweaver-Burk plot for uncompetitive
inhibition compared to no inhibitor?
A. The lines intersect at the y-axis.
B. The lines intersect at the x-axis.
C. The lines intersect in the second quadrant.
D. The lines are parallel to each other.
Answer: D
Rationale: Uncompetitive inhibitors bind only to the enzyme-substrate (ES) complex, not
the free enzyme. This binding reduces both the apparent Vmax and the apparent Km by the
same factor, resulting in a shift of both intercepts on a double-reciprocal plot. Because the
ratio of the slopes remains constant, the resulting lines for inhibited and uninhibited
reactions are parallel.
5. Which amino acids constitute the catalytic triad found in serine proteases like
chymotrypsin?
A. Aspartate, Histidine, and Serine
B. Serine, Histidine, and Lysine
C. Cysteine, Histidine, and Aspartate
D. Serine, Glutamate, and Histidine
Answer: A
