Question

A student conducts an experiment to test how temperature affects enzyme activity. The student observes that the reaction rate increases with temperature up to a point, then sharply declines.



Based on this data and your understanding of protein structure, which claim is best supported by the evidence?

A.
Enzymes are lipids, and high temperatures cause them to dissolve in water, stopping the reaction.

B.
Enzymes are carbohydrates, and heat breaks their sugar bonds, preventing substrate binding.

C.
Enzymes are nucleic acids, and heat causes mutations that prevent them from catalyzing reactions

D.
Enzymes are proteins, and excessive heat denatures their structure, altering the active site and reducing function.

Answer 1

D. Enzymes are proteins, and excessive heat denatures their structure, altering the active site and reducing function.

Explanation: Reaction rate rises with temperature because increased kinetic energy raises collision frequency between enzyme and substrate. Above an optimum temperature, heat disrupts the weak bonds (hydrogen bonds, ionic interactions, hydrophobic packing) that maintain a protein's tertiary/quaternary structure, changing the active site's shape and preventing substrate binding — so activity falls sharply.