Competitive inhibitors reduce reaction rate by...

• A. Completely destroying the enzyme
• B. Resembling the substrate and competing for the active site
• C. Binding to the substrate instead of the enzyme
• D. Increasing enzyme production

Answer: (B)

Competitive inhibition slows a reaction by blocking substrate binding at the enzyme’s active site. The inhibitor mimics the substrate and competes for that same spot, so fewer enzyme–substrate complexes form at a given substrate concentration, lowering the rate. This effect can be overcome by increasing substrate concentration, since more substrate molecules outcompete the inhibitor for the active site. This type of inhibition doesn’t destroy the enzyme, doesn’t involve the inhibitor binding to the substrate, and doesn’t increase enzyme production. The maximum rate (Vmax) can still be reached if substrate levels are high enough, though the apparent affinity (Km) is decreased because more substrate is needed to outcompete the inhibitor.