This set of Biochemistry Multiple Choice Questions & Answers (MCQs) focuses on “Enzyme Kinetics as an Approach to Understanding Mechanism”.
1. Which of the following is true about Michaelis-Menten kinetics?
a) Km, the Michaelis constant, is defined as that concentration of substrate at which enzyme is working at maximum velocity
b) It describes single substrate enzymes
c) Km, the Michaelis constant is defined as the dissociation constant of the enzyme-substrate complex
d) It assumes covalent binding occurs between enzyme and substrate
View Answer
Explanation: Km is defined as the concentration of substrate at which enzyme is working at half of maximum velocity. It is also a measure of the affinity that the enzyme has for its substrate. Michaelis-Menten kinetics assumes non-covalent binding between enzyme and substrate.
2. When the velocity of enzyme activity is plotted against substrate concentration, which of the following is obtained?
a) Hyperbolic curve
b) Parabola
c) Straight line with positive slope
d) Straight line with negative slope
View Answer
Explanation: At low substrate concentration, the rate of a reaction is determined by the rate of formation of an enzyme-substrate complex.
3. Which of the following is the correct Line weaver-Burk equation?
a) \(\frac{1}{V_0} = \frac{K_m}{V_{max} [S]} + \frac{1}{V_{max}} \)
b) \(\frac{1}{V_{max}} = \frac{K_m}{V_0 [S]} + \frac{1}{V_0} \)
c) \(V_0 = \frac{V_{max} [S]}{K_m+[S]} \)
d) \(V_{max} = \frac{V_0 [S]}{K_m+[S]} \)
View Answer
Explanation:
Line weaver-Burk equation: \(\frac{1}{V_0} = \frac{K_m}{V_{max} [S]} + \frac{1}{V_{max}} \)
Michaelis-Menten equation: \(V_0 = \frac{V_{max} [S]}{K_m+[S]} \)
4. Which of the following statements is true about competitive inhibitors?
a) It is a common type of irreversible inhibition
b) In the presence of a competitive inhibitor, the Michaelis-Menten equation becomes
\(V_0 = \frac{V_{max} [S]}{α K_m+[S]} \)
c) The apparent Km decreases in the presence of inhibitor by a factor α
d) The maximum velocity for the reaction decreases in the presence of a competitive inhibitor
View Answer
Explanation: Competitive inhibition is a common type of reversible inhibition.
The apparent Km increases in the presence of inhibitor by a factor α.
The maximum velocity for the reaction remains same in the presence of a competitive inhibitor.
5. Which of the following statements is true about uncompetitive inhibitors?
a) They bind covalently at a site distinct from the substrate active site
b) In the presence of a uncompetitive inhibitor, the Michaelis-Menten equation becomes
\(V_0 = \frac{V_{max} [S]}{K_m+α’ [S]} \)
c) They increase the measured Vmax
d) Apparent Km also increases
View Answer
Explanation: They bind non-covalently at a site distinct from the substrate active site.
They decrease the measured Vmax and also apparent Km.
6. The rate determining step of Michaelis-Menten kinetics is __________
a) The complex dissociation step to produce products
b) The complex formation step
c) The product formation step
d) None of the mentioned
View Answer
Explanation: The breakdown of ES complex is the rate determining step of Michaelis Menten kinetics.
7. The molecule which acts directly on an enzyme to lower its catalytic rate is __________
a) Repressor
b) Inhibitor
c) Modulator
d) Regulator
View Answer
Explanation: An inhibitor is a substance that interferes with the substrate-active site binding and slows down the catalytic rate.
8. Which of the following is an example for irreversible inhibitor?
a) Disulfiram
b) Oseltamivir
c) Protease inhibitors
d) DIPF
View Answer
Explanation: Disulfiram, Oseltamivir and protease inhibitors are reversible inhibitors.
9. Which of the following is an example of reversible inhibitor?
a) DIPF
b) Penicillin
c) Iodoacetamide
d) Protease inhibitors
View Answer
Explanation: DIPF, Penicillin and Iodoacetamide are irreversible inhibitors.
10. Where does inhibitor binds on enzyme in mixed inhibition?
a) At active site
b) Allosteric site
c) Does not bind on enzyme
d) Binds on substrate
View Answer
Explanation: The inhibitor binds at a place different from active site allosterically.
11. The catalytic efficiency of two distinct enzymes can be compared based on which of the following factor?
a) Km
b) Product formation
c) Size of the enzymes
d) pH of optimum value
View Answer
Explanation: Km is the substrate concentration. Increased substrate concentration increases the rate of reaction.
12. What is the general mechanism of an enzyme?
a) It acts by reducing the activation energy
b) It acts by increasing the activation energy
c) It acts by decreasing the pH
d) It acts by increasing the pH
View Answer
Explanation: For the reaction to occur at a faster rate, activation energy should be less.
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