MCAT Biochemistry Question 25: Answer and Explanation

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Question: 25

10. The graph below shows kinetic data obtained for flu virus enzyme activity as a function of substrate concentration in the presence and absence of two antiviral drugs.

Based on the graph, which of the following statements is correct?

A. Both drugs are noncompetitive inhibitors of the viral enzyme.
B. Tamiflu increases the K_m value for the substrate compared to Relenza.
C. Relenza increases the v_max value for the substrate compared to Tamiflu.
D. Both drugs are competitive inhibitors of the viral enzyme.

Correct Answer: B

Explanation:

Based on the graph, when the substrate is present, Tamiflu results in the same v_max and a higher K_m compared to when no inhibitor is added. These are hallmarks of competitive inhibitors. Noncompetitive inhibitors result in decreased v_max and the same K_m as the uninhibited reaction, which is shown by the Relenza line in the graph. Because the question is only comparing the values between the two inhibitors, and not the enzyme without inhibitor, the mechanism of inhibition is less important to determine than the values of K_m and v_max. This is a great example of why previewing the answer choices works well in the sciences.

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