CHEM 210 Biochemistry Module 3: Enzymes and Kinetics Exam
2026/2027 UPDATE
1. What is the primary role of an enzyme in a biochemical reaction?
A. To lower the activation energy required for the reaction
B. To increase the standard free energy change of the reaction
C. To shift the equilibrium constant toward the products
D. To increase the temperature of the reaction environment
Answer: A
Rationale: Enzymes act as catalysts by lowering the activation energy barrier, allowing the
reaction to proceed faster without changing the overall equilibrium or free energy.
2. The specific region of an enzyme where the substrate binds and catalysis
occurs is called the:
A. Active site
B. Apoenzyme
C. Allosteric site
D. Regulatory site
Answer: A
Rationale: The active site is the pocket or cleft in the enzyme’s structure where the
substrate fits and the chemical reaction takes place.
,3. According to the Michaelis-Menten model, what does the constant Km
represent?
A. The maximum velocity of the reaction
B. The substrate concentration at which the reaction velocity is half of Vmax
C. The equilibrium constant for the total reaction
D. The rate constant for the formation of product
Answer: B
Rationale: Km (the Michaelis constant) is defined as the substrate concentration [S] at
which the initial reaction velocity is exactly half of the maximum velocity (Vmax).
4. In a Lineweaver-Burk plot, the y-intercept is equal to:
A. 1/Vmax
B. -1/Km
C. Km/Vmax
D. Vmax/Km
Answer: A
Rationale: The double-reciprocal Lineweaver-Burk equation is 1/v = (Km/Vmax)(1/[S]) +
1/Vmax. The y-intercept occurs when 1/[S] is zero, yielding 1/Vmax.
5. Which type of inhibitor binds only to the enzyme-substrate (ES) complex and
not to the free enzyme?
A. Competitive inhibitor
B. Non-competitive inhibitor
C. Uncompetitive inhibitor
D. Mixed inhibitor
Answer: C
Rationale: Uncompetitive inhibitors bind exclusively to the ES complex, preventing the
reaction from completing. This typically lowers both Vmax and Km.
, 6. How does a competitive inhibitor affect the kinetic parameters of an enzyme?
A. Decreases Vmax and increases Km
B. Leaves Vmax unchanged and increases Km
C. Increases Vmax and leaves Km unchanged
D. Decreases both Vmax and Km
Answer: B
Rationale: Competitive inhibitors compete with the substrate for the active site. Increasing
substrate can overcome the inhibitor, so Vmax remains the same, but the apparent affinity
decreases (Km increases).
7. An enzyme that is catalytically active only when combined with its required
cofactor is called a(n):
A. Apoenzyme
B. Holoenzyme
C. Zymogen
D. Isozyme
Answer: B
Rationale: A holoenzyme is the complete, active form of an enzyme consisting of the
protein part (apoenzyme) and the necessary non-protein component (cofactor).
8. The ‘induced fit’ model of enzyme action suggests that:
A. The enzyme and substrate are rigid and fit like a key in a lock
B. The substrate changes shape to fit the enzyme’s rigid active site
C. The enzyme is permanently altered after each reaction
D. The enzyme changes shape upon substrate binding to optimize the fit
Answer: D
Rationale: Induced fit describes the dynamic change in the enzyme’s conformation when
the substrate binds, ensuring a more precise orientation for catalysis.
2026/2027 UPDATE
1. What is the primary role of an enzyme in a biochemical reaction?
A. To lower the activation energy required for the reaction
B. To increase the standard free energy change of the reaction
C. To shift the equilibrium constant toward the products
D. To increase the temperature of the reaction environment
Answer: A
Rationale: Enzymes act as catalysts by lowering the activation energy barrier, allowing the
reaction to proceed faster without changing the overall equilibrium or free energy.
2. The specific region of an enzyme where the substrate binds and catalysis
occurs is called the:
A. Active site
B. Apoenzyme
C. Allosteric site
D. Regulatory site
Answer: A
Rationale: The active site is the pocket or cleft in the enzyme’s structure where the
substrate fits and the chemical reaction takes place.
,3. According to the Michaelis-Menten model, what does the constant Km
represent?
A. The maximum velocity of the reaction
B. The substrate concentration at which the reaction velocity is half of Vmax
C. The equilibrium constant for the total reaction
D. The rate constant for the formation of product
Answer: B
Rationale: Km (the Michaelis constant) is defined as the substrate concentration [S] at
which the initial reaction velocity is exactly half of the maximum velocity (Vmax).
4. In a Lineweaver-Burk plot, the y-intercept is equal to:
A. 1/Vmax
B. -1/Km
C. Km/Vmax
D. Vmax/Km
Answer: A
Rationale: The double-reciprocal Lineweaver-Burk equation is 1/v = (Km/Vmax)(1/[S]) +
1/Vmax. The y-intercept occurs when 1/[S] is zero, yielding 1/Vmax.
5. Which type of inhibitor binds only to the enzyme-substrate (ES) complex and
not to the free enzyme?
A. Competitive inhibitor
B. Non-competitive inhibitor
C. Uncompetitive inhibitor
D. Mixed inhibitor
Answer: C
Rationale: Uncompetitive inhibitors bind exclusively to the ES complex, preventing the
reaction from completing. This typically lowers both Vmax and Km.
, 6. How does a competitive inhibitor affect the kinetic parameters of an enzyme?
A. Decreases Vmax and increases Km
B. Leaves Vmax unchanged and increases Km
C. Increases Vmax and leaves Km unchanged
D. Decreases both Vmax and Km
Answer: B
Rationale: Competitive inhibitors compete with the substrate for the active site. Increasing
substrate can overcome the inhibitor, so Vmax remains the same, but the apparent affinity
decreases (Km increases).
7. An enzyme that is catalytically active only when combined with its required
cofactor is called a(n):
A. Apoenzyme
B. Holoenzyme
C. Zymogen
D. Isozyme
Answer: B
Rationale: A holoenzyme is the complete, active form of an enzyme consisting of the
protein part (apoenzyme) and the necessary non-protein component (cofactor).
8. The ‘induced fit’ model of enzyme action suggests that:
A. The enzyme and substrate are rigid and fit like a key in a lock
B. The substrate changes shape to fit the enzyme’s rigid active site
C. The enzyme is permanently altered after each reaction
D. The enzyme changes shape upon substrate binding to optimize the fit
Answer: D
Rationale: Induced fit describes the dynamic change in the enzyme’s conformation when
the substrate binds, ensuring a more precise orientation for catalysis.
