Explain how the structure of an enzyme allows it to carry out its function, and describe what happens to the enzyme when the temperature rises significantly above its optimum.

Eduqas A-Level Biology — 1.2 Cell structure and organisation · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

1. Enzymes have an active site with a specific shape.
2. The shape of the active site is complementary to the substrate.
3. The substrate binds to the active site, forming an enzyme‑substrate complex.
4. At temperatures far above the optimum the enzyme becomes denatured.
5. Denaturation permanently changes the shape of the active site, so the substrate can no longer fit and no enzyme‑substrate complexes form.

Examiner tips

  • Use the keyword ‘active site’ and ‘substrate’ to show understanding of structure. Show the sequence: active site → complementary shape → binding → complex. Mention denaturation and permanent shape change. Keep each point concise to fit the 5‑mark limit.

Common mistakes

  • Confusing ‘denatured’ with ‘inactivated’ without explaining shape change. Using vague terms like ‘change in shape’ without linking to substrate binding. Omitting the step that the substrate binds to form a complex.

Mark scheme (5 marks)

  1. The enzyme has an active site with a specific shape
  2. The shape of the active site is complementary to the substrate
  3. An enzyme-substrate complex forms / the substrate binds to the active site
  4. At temperatures significantly above the optimum, the enzyme becomes denatured
  5. The shape of the active site changes permanently, so the substrate can no longer fit / no enzyme-substrate complexes can form

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