Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologyhardmcq1 pt

A pure noncompetitive inhibitor binds an enzyme at a site distinct from the active site. Which kinetic pattern is expected?

A.Apparent Km rises while Vmax stays reachable, because extra substrate can eventually win the active site back
B.Vmax decreases while Km stays roughly unchanged, because inhibited enzyme molecules are idle yet surviving enzyme binds substrate normally
C.Both Vmax and Km fall, because the inhibitor helps substrate dock at lower concentrations
D.Kinetic parameters disappear because the inhibitor destroys every enzyme molecule covalently

Explanation

Core Concept

For pure noncompetitive inhibition, inhibitor binding reduces the concentration of catalytically active enzyme, so Vmax decreases. Because the inhibitor binds free enzyme and enzyme–substrate complex equally, substrate affinity is unchanged and Km remains approximately the same. Mixed inhibition can alter Km, so the word 'pure' is necessary.

Correct Answer

BVmax decreases while Km stays roughly unchanged, because inhibited enzyme molecules are idle yet surviving enzyme binds substrate normally

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