Final answer:
An inhibitor affects an enzyme by preventing a substrate from binding, either by direct competition at the active site or through conformational changes of the enzyme induced by binding at different sites.
Step-by-step explanation:
The effect of an inhibitor on an enzyme is to interfere with its normal function, which is to catalyze chemical reactions. When an inhibitor binds to an enzyme, it can prevent a substrate from attaching to the enzyme. Depending on the type of inhibitor, the binding can occur at the active site of the enzyme (competitive inhibition) or at a different site (noncompetitive or allosteric inhibition). If it binds at the active site, it competes with the substrate for the site, thereby preventing substrate binding and subsequent reaction. This is known as competitive inhibition. When an inhibitor binds to a site other than the active site, it can cause a conformational change in the enzyme that either reduces the enzyme's affinity for the substrate (allosteric inhibition) or completely alters the active site (noncompetitive inhibition).