Amylase is an enzyme found in saliva that breaks down starch into maltose. Explain why amylase continues to work after it has broken down a starch molecule.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Amylase is a protein catalyst that is not consumed in the reaction.
The maltose product dissociates from the enzyme’s active site.
The active site is then free to bind a new starch molecule.
A new enzyme–substrate complex can form and the cycle repeats.
The maltose product dissociates from the enzyme’s active site.
The active site is then free to bind a new starch molecule.
A new enzyme–substrate complex can form and the cycle repeats.
Examiner tips
- Use the term ‘catalyst’ to show it is not used up. Mention ‘product dissociates’ to demonstrate release. State that the active site becomes free. Show that a new complex can form – this shows the cycle continues.
Common mistakes
- Confusing the enzyme with the substrate. Saying the enzyme is ‘used up’ or ‘destroyed’. Omitting the step that the product leaves the active site.
Mark scheme (4 marks)
- The enzyme is not changed/used up by the reaction
- The product is released from the active site
- The active site is free/available to bind to another substrate molecule
- A new enzyme-substrate complex can form
Key terms in this question
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →