What defines a competitive inhibitor in enzyme activity?

A competitive inhibitor is defined by its ability to bind to the active site of an enzyme, effectively blocking the substrate from attaching. This type of inhibition occurs because the structure of the competitive inhibitor often resembles that of the substrate, allowing it to compete for binding at the same site. When the competitive inhibitor is bound to the active site, the enzyme cannot catalyze the reaction that would normally occur with the substrate. This can lead to a decrease in the overall rate of the reaction, as the presence of the inhibitor inhibits substrate binding and reduces product formation. The key factor in competitive inhibition is the direct competition between the inhibitor and substrate for the active site, which differentiates it from other types of inhibition, such as non-competitive inhibition, where the inhibitor binds to a different site on the enzyme.