Advanced Placement (AP) Biology Practice Exam

What type of inhibition occurs when an inhibitor competes with the substrate for binding to the enzyme?

1. Non-competitive inhibition

2. Competitive inhibition

3. Allosteric inhibition

4. Feedback inhibition

The correct answer is: Competitive inhibition

Competitive inhibition occurs when an inhibitor competes with the substrate for the active site of the enzyme. In this scenario, both the substrate and the inhibitor are trying to bind to the same location on the enzyme. Because they vie for the same binding site, the presence of the inhibitor can prevent the substrate from binding effectively, thereby decreasing the rate of the enzymatic reaction. This type of inhibition can often be overcome by increasing the concentration of the substrate. If substrate concentrations are high enough, they can outcompete the inhibitor for the active site, restoring the enzyme's activity. This characteristic distinguishes competitive inhibition from other forms of inhibition, where the inhibitor may bind to a different site or change the enzyme's shape, making it less effective regardless of substrate concentration. Non-competitive inhibition, allosteric inhibition, and feedback inhibition involve different mechanisms that do not involve direct competition for the active site, thus highlighting the unique nature of competitive inhibition.