Explain why a protein loses its function when it is denatured.

IB DP Biology Standard 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 hydrogen, ionic and disulfide bonds that stabilise the protein’s tertiary structure. The loss of these bonds alters or destroys the three‑dimensional shape of the protein. As a result the active or binding site changes shape, so substrates or ligands can no longer fit or bind. Because the function of a protein depends on its specific shape, any change in conformation prevents the protein from carrying out its role, such as catalysis, transport or signalling.

Examiner tips

  • Use the term ‘tertiary structure’ and mention the specific bonds broken. Include the effect on the active site and the loss of function. Keep the answer concise and directly linked to the marks.

Common mistakes

  • Confusing denaturation with degradation or mis‑labeling the bonds involved; writing about primary structure instead of tertiary.

Mark scheme (4 marks)

  1. Denaturation involves the breaking of bonds (hydrogen bonds / ionic bonds / disulfide bonds) that maintain the tertiary structure of the protein.
  2. The tertiary (three-dimensional) shape / conformation of the protein is altered / lost.
  3. The active site (or binding site) changes shape, so substrate / ligand can no longer fit / bind.
  4. Function depends on the specific shape of the protein, so any change in shape prevents the protein from carrying out its role (e.g., catalysis, transport, signalling).

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