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

A purified enzyme loses catalytic activity after brief exposure to 80 degrees Celsius. Chemical analysis shows every peptide bond remains intact. Which explanation accounts for the lost function?

A.Primary structure was randomized because sequence order depends on temperature.
B.Heat disrupted the hydrogen bonds and hydrophobic interactions that maintain tertiary structure.
C.Water was removed from the solution, breaking the protein into amino acids.
D.Substrate molecules denatured first, leaving the enzyme with nothing to bind.

Explanation

Core Concept

Protein function depends on precise three-dimensional folding held together by weak interactions such as hydrogen bonds, ionic attractions, and hydrophobic clustering among side chains. Heat increases molecular motion until these forces fail while the strong covalent peptide bonds of the backbone survive. The polypeptide unfolds, the active site loses its geometry, and catalysis stops even though the chain itself is unbroken. Denaturation therefore destroys higher-order structure, never primary structure, which explains why analysis still finds every peptide linkage in place.

Correct Answer

BHeat disrupted the hydrogen bonds and hydrophobic interactions that maintain tertiary structure.

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