Catalase is an enzyme found in liver cells that breaks down hydrogen peroxide into water and oxygen. Explain how the structure of catalase allows it to act as a biological catalyst, and describe what happens to the enzyme when it is boiled.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Catalase is a protein made from chains of amino acids that fold to give it a specific shape.
The folded protein contains an active site whose shape is complementary to the hydrogen peroxide substrate.
When hydrogen peroxide binds to the active site, an enzyme‑substrate complex is formed.
The reaction proceeds, but the enzyme is not chemically altered; it is released unchanged and can act again.
If the enzyme is boiled, the protein denatures – the active‑site shape changes permanently, preventing complex formation and the reaction stops.
The folded protein contains an active site whose shape is complementary to the hydrogen peroxide substrate.
When hydrogen peroxide binds to the active site, an enzyme‑substrate complex is formed.
The reaction proceeds, but the enzyme is not chemically altered; it is released unchanged and can act again.
If the enzyme is boiled, the protein denatures – the active‑site shape changes permanently, preventing complex formation and the reaction stops.
Examiner tips
- Use the term ‘active site’ and ‘enzyme‑substrate complex’.
- Show that the enzyme is unchanged after the reaction.
- Explain denaturation as permanent loss of shape.
Mark scheme (5 marks)
- Catalase is a protein made from chains of amino acids that fold to give it a specific shape
- Catalase has an active site with a shape complementary to the hydrogen peroxide substrate
- The substrate (hydrogen peroxide) enters the active site to form an enzyme-substrate complex
- The enzyme is not changed / is released unchanged and can be reused / acts repeatedly
- Boiling causes denaturation — the shape of the active site changes permanently so no enzyme-substrate complexes can form and the rate of reaction decreases / stops
Key terms in this question
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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