Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologymediummcq1 pt

An enzyme's reaction rate climbs steadily from 10 degrees Celsius to a peak near 40 degrees Celsius, then collapses almost to zero by 55 degrees Celsius. Which explanation accounts for both parts of the curve?

A.Cold temperatures denature the enzyme, and warming gradually refolds it.
B.Heat lowers the activation energy below what the enzyme requires at low temperature.
C.At high temperature the substrate decomposes faster than any enzyme could act.
D.Moderate heating raises molecular motion and collision frequency, but past the peak it breaks hydrogen bonds and ionic interactions that hold the active site shape.

Explanation

Core Concept

Below the optimum, warmer molecules move and collide more often, so more enzyme-substrate encounters occur each second and the rate climbs. Beyond the optimum, thermal agitation overwhelms the weak bonds maintaining tertiary structure. The active site distorts, substrates fit poorly, and catalysis plunges, often irreversibly once the protein unfolds. One physical account, kinetic boost then structural failure, covers the whole curve.

Correct Answer

DModerate heating raises molecular motion and collision frequency, but past the peak it breaks hydrogen bonds and ionic interactions that hold the active site shape.

More Unit 3: Cellular Energetics practice questions

Try a random question →

Practice more AP Biology questions with full explanations

Practice Unit 3: Cellular Energetics Questions →