A current problem in modern medicine is the development of drug resistance mutations. This occurs when a mutation arises in a disease-causing microbe making it resistant to a drug and thus rendering the drug useless in treating a specific disease. Many useful drugs are competitive inhibitors of specific enzymes, and the drug-resistance mutations prevent the binding of the drug. These types of mutations, in addition to preventing competitive inhibitor binding, can also sometimes reduce the activity of the enzyme. Why is that the case? a. Binding to the competitive inhibitor is essential for the function of the enzyme. b. These mutations most likely affect an allosteric site on the enzyme. c. These mutations lower the activation energy of the reaction catalyzed by the enzyme. d. These mutations most likely change the shape of the active site of the enzyme.

d. These mutations most likely change the shape of the active site of the enzyme.

Explanation:

A competitive inhibitor competes with an enzyme substrate for the binding of the enzyme. When it binds, the enzyme substrate cannot bind unless the inhibitor is removed from the active site by some mechanism.

The ability of a competitive inhibitor of an enzyme to function is due to the fact that these inhibitors are structurally similar to the enzyme's substrate.

So when a mutation which also affects the activity occurs in a microbe, that renders it resistant to a drug serving as a competitive inhibitor of that enzyme in the microbe, most likely, this resistance is due to a structural change in the enzyme which changes the shape of the enzyme's active site. Therefore, both the drug as well as the enzyme's substrate, will be unable to bind to the enzymes active site.

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