Question

a noncompetitive inhibitor decreases the rate of an enzymatic reaction by...
binding to the active site of the enzyme.
changing the ag for the reaction.
changing the shape of the enzyme active site.
decreasing the activation energy required for the reaction.

Explanation:

A non - competitive inhibitor binds to an allosteric site (not the active site) of the enzyme. This binding causes a conformational change in the enzyme's active site. The change in the active site shape reduces the enzyme's ability to bind to its substrate effectively, thus decreasing the rate of the enzymatic reaction.

• Binding to the active site is characteristic of competitive inhibitors.
• Enzymes (and their inhibitors) do not change the $\Delta G$ of a reaction. They only affect the rate (by changing the activation energy). A non - competitive inhibitor does not decrease the activation energy; instead, it makes the enzyme less effective at lowering the activation energy by altering its active site shape.

Answer:

changing the shape of the enzyme active site.