Competitive inhibition and reaction rate

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LakridsA

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Ritonavir is an anti-viral drug that mimics the natural substrate for a key viral protease enzyme. As a competitive inhibitor, ritonavir:

decreases the rate of reaction because it decreases the availability of ATP to catalyze the reaction.

increases the rate of reaction by altering the tertiary structure of the enzyme.

decreases the rate of reaction by binding to the enzyme and altering the structure of its active site.

decreases the rate of reaction by binding to the active site.

I always thought competitive inhibition had no effect on the Vmax?? But all answer choices talk about a change in the reaction rate?

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You are correct, competitive inhibition does not affect Vmax, which is when the substrate concentration is very high. But it does still affect the rate of the reaction at other substrate concentrations. If you have 2 things competing for the same enzyme, the substrate will bind to the enzyme less, so the rate of the conversion of substrate to product will decrease. Vmax doesn't change though because when the substrate concentration is much higher than the concentration of the inhibitor, the inhibitor has no effect.

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