Describe what happens when a substrate molecule binds to an enzyme and explain how the product is released.

Cambridge International IGCSE Biology (0610) — 5.1 Enzymes · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

The substrate enters the active site of the enzyme.
An enzyme‑substrate complex is formed.
The substrate is broken down into product(s).
The product(s) are released and the enzyme is unchanged and can be reused.

Examiner tips

Use the sequence: binding → complex → reaction → release. Mention the active site explicitly. Show that the enzyme is unchanged after the reaction.

Common mistakes

Forgetting to state that the enzyme is unchanged. Describing the reaction as a change in the enzyme rather than the substrate. Using vague terms like "the enzyme does something" without specifying binding or release.

Mark scheme (4 marks)

The substrate enters / binds to the active site of the enzyme
An enzyme-substrate complex is formed
The substrate is broken down (into products)
The product(s) are released and the enzyme is unchanged / can be reused

Key terms in this question

substrate