In competitive inhibition, what does the inhibitor do?

• A. Binds to active site and competes with substrate
• B. Binds to allosteric site
• C. Denatures enzyme
• D. Increases substrate concentration

Answer: (A)

In competitive inhibition the inhibitor targets the active site itself, fitting in like the substrate and blocking substrate binding. This competition can be overcome by raising the substrate concentration, because the substrate is more likely to occupy the active site when it’s abundant. The enzyme’s maximum rate (Vmax) stays the same, since once substrate does bind, the catalysis proceeds normally, but the apparent affinity for substrate increases (Km appears higher) because more substrate is needed to reach half-maximal velocity. This differs from inhibitors that bind elsewhere (allosteric sites) or that unfold or denature the enzyme, which would change Vmax or enzyme stability rather than simply blocking the active site.