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Which of the following statements about Michaelis-Menten kinetics is correct?
a) Km, the Michaelis constant, is defined as the concentration of substrate required for the reaction to reach maximum velocity.
b) Km, the Michaelis constant, is defined as the dissociation constant of the enzyme-substrate complex.
c) Km, the Michaelis constant, is expressed in terms of the reaction velocity.
d) Km, the Michaelis constant, is a measure of the affinity the enzyme has for its substrate.
Question 4
Which of the following statements about the competitive inhibition of an enzyme-catalyzed reaction is correct?
a) A competitive inhibitor and substrate can bind simultaneously to the enzyme.
b) The Vmax and Km (Michaelis constant) for a reaction are unchanged in the presence of a competitive inhibitor.
c) The Vmax for a reaction remains unchanged in the presence of a competitive inhibitor.
d) The Km for a reaction remains unchanged in the presence of a competitive inhibitor.
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Which of the following statements about Michaelis-Menten kinetics is correct?
Your Answer:
d) Km, the Michaelis constant, is a measure of the affinity the enzyme has for its substrate.
Feedback:
An enzyme that displays hyperbolic kinetics (single substrate enzyme) is referred to as a Michaelis-Menten enzyme. For such an enzyme, the plot of velocity of the reaction against substrate concentration is hyperbolic. The Michaelis-Menten equation describes the kinetics of such an enzyme at initial rates before any product is formed. The Michaelis-Menten equation can be used to calculate the Michaelis constant (Km). This is defined as that concentration of substrate at which the enzyme is working at half maximum velocity. Km is expressed in units of molar concentration and is independent of the enzyme concentration. Km is also a measure of the affinity that the enzyme has for its substrate. The higher the Km, the lower the affinity of the enzyme for its substrate.
Page reference: page 91
Question 4
Which of the following statements about the competitive inhibition of an enzyme-catalyzed reaction is correct?
Your Answer:
c) The Vmax for a reaction remains unchanged in the presence of a competitive inhibitor.
Feedback:
Competitive inhibitors have a similar structure to the substrate and compete with the latter for binding to the active site of an enzyme. A competitive inhibitor binds reversibly to the active site. It will have no effect on the reaction at infinite substrate concentration since the substrate will win in the competition to bind to the enzyme active site. Consequently a competitive inhibitor and substrate cannot bind simultaneously to the enzyme. A comparison of the double reciprocal plots of an enzyme reaction with and without competitive inhibitor shows that:
1) Vmax, the maximum velocity for the reaction, remains unchanged in the presence of a competitive inhibitor
2) Km, the Michaelis constant for the reaction, increases in the presence of a competitive inhibitor. This is because the affinity that the enzyme has for its substrate is reduced in the presence of a competitive inhibitor.
Page reference: Page 93
