Competitive inhibition
MCAT glossary · Biological & Biochemical Foundations of Living Systems
Definition
Inhibitor binds the enzyme active site, raising apparent Km while leaving Vmax unchanged.
Competitive inhibition in plain English
Enzymes are helpers that speed up chemical reactions, and they work by grabbing their target molecule in a special pocket called the active site. A competitive inhibitor is an impostor that fits into that same pocket, blocking the real molecule from getting in — like someone taking the one parking spot your car needed. The good news is it's a fair fight: if you flood the area with enough of the real molecule, it out-competes the impostor and the enzyme can still hit full speed (V_max is unchanged). It just takes more of the real molecule to get there, which is why we say the apparent K_m (roughly, the amount needed to work at half-speed) goes up.
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