BCH5413 Advanced Biochemistry Exam 1 Prep: Master
Enzyme Kinetics, Metabolism, and Thermodynamics
Practice Questions & Detailed Explanations
Subject: Enzyme Kinetics, Bioenergetics, and Metabolic Regulation
Question 1: In a bisubstrate reaction following a Ping-Pong (double-displacement) mechanism,
which of the following best describes the kinetic pattern observed on a Lineweaver-Burk plot as
the concentration of the second substrate is varied at several fixed concentrations of the first
substrate?
A) The lines intersect at a point to the left of the y-axis.
B) The lines are parallel to each other.
C) The lines intersect on the y-axis.
D) The lines intersect on the x-axis.
Correct Answer: B) The lines are parallel to each other.
Explanation: In a Ping-Pong mechanism, the first substrate binds and a product is released
before the second substrate binds. This results in parallel lines in a Lineweaver-Burk plot
because the ratio of $V_{max}/K_m$ remains constant as the concentration of the second
substrate changes, unlike sequential mechanisms where the lines would intersect.
Question 2: Which parameter is most significantly affected by a non-competitive inhibitor in a
Michaelis-Menten enzyme system?
A) The Michaelis constant ($K_m$).
B) The maximum velocity ($V_{max}$).
C) Both $K_m$ and $V_{max}$ in equal proportions.
D) The substrate binding affinity ($K_d$).
Correct Answer: B) The maximum velocity ($V_{max}$).
Explanation: A non-competitive inhibitor binds to both the free enzyme and the enzyme-substrate
complex with equal affinity, effectively reducing the concentration of functional enzyme. This
decreases $V_{max}$ but leaves $K_m$ unchanged because the inhibitor does not interfere with
the binding of the substrate.
, Question 3: A metabolic pathway is regulated by allosteric feedback inhibition. If a downstream
product binds to a regulatory site on the committed step enzyme, what occurs to the
conformational state of the enzyme?
A) It shifts toward the T-state (tense), decreasing substrate affinity.
B) It shifts toward the R-state (relaxed), increasing catalytic turnover.
C) It remains in the T-state but undergoes phosphorylation.
D) It converts the enzyme into a monomeric form to reduce activity.
Correct Answer: A) It shifts toward the T-state (tense), decreasing substrate affinity.
Explanation: Allosteric inhibitors of metabolic pathways typically stabilize the T-state, which
has a lower affinity for the substrate. This ensures that when the pathway product is abundant,
the commitment to the pathway is reduced, conserving cellular resources.
Question 4: Given an enzyme with a $k_{cat}$ of $500 \text{ s}^{-1}$ and a $K_m$ of $0.05
\text{ mM}$, what is the catalytic efficiency of the enzyme?
A) $100 \text{ mM}^{-1} \text{ s}^{-1}$
B) $1,000 \text{ mM}^{-1} \text{ s}^{-1}$
C) $10,000 \text{ mM}^{-1} \text{ s}^{-1}$
D) $25,000 \text{ mM}^{-1} \text{ s}^{-1}$
Correct Answer: C) $10,000 \text{ mM}^{-1} \text{ s}^{-1}$
Explanation: Catalytic efficiency is defined by the ratio $k_{cat}/K_m$. Here, $500 \text{ s}^{-
1} / 0.05 \text{ mM} = 10,000 \text{ mM}^{-1} \text{ s}^{-1}$. This value describes how well an
enzyme performs when substrate concentration is low.
Question 5: Which of the following thermodynamic values must be negative for a reaction to
occur spontaneously under standard conditions?
A) $\Delta G^{\circ'}$
B) $\Delta H^{\circ'}$
C) $\Delta S^{\circ'}$
D) $\Delta E^{\circ'}$
Enzyme Kinetics, Metabolism, and Thermodynamics
Practice Questions & Detailed Explanations
Subject: Enzyme Kinetics, Bioenergetics, and Metabolic Regulation
Question 1: In a bisubstrate reaction following a Ping-Pong (double-displacement) mechanism,
which of the following best describes the kinetic pattern observed on a Lineweaver-Burk plot as
the concentration of the second substrate is varied at several fixed concentrations of the first
substrate?
A) The lines intersect at a point to the left of the y-axis.
B) The lines are parallel to each other.
C) The lines intersect on the y-axis.
D) The lines intersect on the x-axis.
Correct Answer: B) The lines are parallel to each other.
Explanation: In a Ping-Pong mechanism, the first substrate binds and a product is released
before the second substrate binds. This results in parallel lines in a Lineweaver-Burk plot
because the ratio of $V_{max}/K_m$ remains constant as the concentration of the second
substrate changes, unlike sequential mechanisms where the lines would intersect.
Question 2: Which parameter is most significantly affected by a non-competitive inhibitor in a
Michaelis-Menten enzyme system?
A) The Michaelis constant ($K_m$).
B) The maximum velocity ($V_{max}$).
C) Both $K_m$ and $V_{max}$ in equal proportions.
D) The substrate binding affinity ($K_d$).
Correct Answer: B) The maximum velocity ($V_{max}$).
Explanation: A non-competitive inhibitor binds to both the free enzyme and the enzyme-substrate
complex with equal affinity, effectively reducing the concentration of functional enzyme. This
decreases $V_{max}$ but leaves $K_m$ unchanged because the inhibitor does not interfere with
the binding of the substrate.
, Question 3: A metabolic pathway is regulated by allosteric feedback inhibition. If a downstream
product binds to a regulatory site on the committed step enzyme, what occurs to the
conformational state of the enzyme?
A) It shifts toward the T-state (tense), decreasing substrate affinity.
B) It shifts toward the R-state (relaxed), increasing catalytic turnover.
C) It remains in the T-state but undergoes phosphorylation.
D) It converts the enzyme into a monomeric form to reduce activity.
Correct Answer: A) It shifts toward the T-state (tense), decreasing substrate affinity.
Explanation: Allosteric inhibitors of metabolic pathways typically stabilize the T-state, which
has a lower affinity for the substrate. This ensures that when the pathway product is abundant,
the commitment to the pathway is reduced, conserving cellular resources.
Question 4: Given an enzyme with a $k_{cat}$ of $500 \text{ s}^{-1}$ and a $K_m$ of $0.05
\text{ mM}$, what is the catalytic efficiency of the enzyme?
A) $100 \text{ mM}^{-1} \text{ s}^{-1}$
B) $1,000 \text{ mM}^{-1} \text{ s}^{-1}$
C) $10,000 \text{ mM}^{-1} \text{ s}^{-1}$
D) $25,000 \text{ mM}^{-1} \text{ s}^{-1}$
Correct Answer: C) $10,000 \text{ mM}^{-1} \text{ s}^{-1}$
Explanation: Catalytic efficiency is defined by the ratio $k_{cat}/K_m$. Here, $500 \text{ s}^{-
1} / 0.05 \text{ mM} = 10,000 \text{ mM}^{-1} \text{ s}^{-1}$. This value describes how well an
enzyme performs when substrate concentration is low.
Question 5: Which of the following thermodynamic values must be negative for a reaction to
occur spontaneously under standard conditions?
A) $\Delta G^{\circ'}$
B) $\Delta H^{\circ'}$
C) $\Delta S^{\circ'}$
D) $\Delta E^{\circ'}$
