Apentix/AP Biology/Unit 1: Chemistry of Life/Question
AP Biologymediummcq1 pt

Pepsin digests protein near pH 2 in the stomach, while trypsin works near pH 8 in the small intestine. Why does each enzyme lose activity when moved outside its optimal pH range?

A.Ionization states of active-site side chains shift, altering enzyme shape and substrate binding.
B.Hydrogen ions directly hydrolyze the enzyme's peptide bonds whenever pH deviates from the optimum.
C.Substrates precipitate outside the optimal range, so nothing reaches the active site.
D.Extreme pH decomposes the enzyme into individual amino acids within seconds.

Explanation

Core Concept

Enzyme activity depends on the charge pattern of the active site. Side chains such as histidine, aspartate, and lysine gain or lose protons as pH changes, disrupting ionic interactions and hydrogen bonds that hold the tertiary structure together and participate directly in catalysis. With charges altered, the active site no longer binds substrate in a productive orientation and the reaction rate falls sharply. Different sequences stabilize different charge patterns, which is why pepsin and trypsin have distinct optima matched to their environments.

Correct Answer

AIonization states of active-site side chains shift, altering enzyme shape and substrate binding.

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