Enzyme Catalysis

AP Biology· difficulty 2/5

A student measured initial reaction rate of an enzyme at increasing substrate concentrations and produced the curve shown.

[Substrate] Rate (V) Vmax Km

The graph shows enzyme reaction rate vs substrate concentration. What does Km represent?

  • A

    Rate at which enzyme denatures under increased substrate

  • B

    Substrate concentration at which enzyme activity stops

  • C

    Maximum reaction rate when enzyme is fully saturated

  • D

    Substrate concentration at half Vmax, indicating enzyme-substrate affinity

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Explanation

Km (Michaelis constant) is the substrate concentration at which the reaction rate equals 1/2 Vmax. A lower Km indicates higher affinity between enzyme and substrate.

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