Explain why denaturation of an enzyme results in loss of its catalytic activity.

IB DP Biology Higher Level (2023 syllabus) — B1.2 Proteins · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Denaturation breaks the non‑covalent bonds that maintain the enzyme’s tertiary structure, causing it to unfold. The altered three‑dimensional conformation changes the shape of the active site, so the substrate can no longer bind. Without substrate binding the enzyme–substrate complex cannot form and the enzyme cannot lower the activation energy, so catalytic activity is lost.

Examiner tips

Show the chain: denaturation → loss of tertiary structure → altered active site → no substrate binding → no catalysis
Use terms: hydrogen bonds, ionic bonds, hydrophobic interactions, tertiary structure, active site, induced fit

Common mistakes

Confusing denaturation with irreversible inactivation; forgetting to mention loss of substrate binding
Using vague phrases like ‘enzyme is damaged’ without linking to structure and activity

Mark scheme (4 marks)

Denaturation disrupts non-covalent interactions (hydrogen bonds, ionic bonds, hydrophobic interactions) that maintain tertiary structure
The three-dimensional (tertiary) structure / conformation of the enzyme is altered / unfolded
The active site changes shape so substrate can no longer bind (induced fit / complementary shape is lost)
Without substrate binding, the enzyme–substrate complex cannot form and so catalysis / lowering of activation energy does not occur

Key terms in this question

denaturation