Amylase is an enzyme that breaks down starch into simple sugars. Describe how the structure of amylase allows it to carry out this function, and explain what is meant by enzyme specificity.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Amylase is a protein made from chains of amino acids.
Its three‑dimensional structure creates an active site with a specific, complementary shape.
The starch molecule (substrate) fits into this active site, forming an enzyme‑substrate complex.
Enzyme specificity means that only substrates whose shape matches the active site are acted on – amylase will only act on starch.
Because other molecules such as proteins or lipids do not fit the active site, amylase cannot break them down.
Its three‑dimensional structure creates an active site with a specific, complementary shape.
The starch molecule (substrate) fits into this active site, forming an enzyme‑substrate complex.
Enzyme specificity means that only substrates whose shape matches the active site are acted on – amylase will only act on starch.
Because other molecules such as proteins or lipids do not fit the active site, amylase cannot break them down.
Examiner tips
- Use the word ‘active site’ and describe its complementary shape. Show the enzyme‑substrate complex. Explain specificity as ‘only one substrate fits the active site’. Mention that other molecules are not acted on because of shape mismatch.
Common mistakes
- Confusing enzyme with substrate. Saying amylase breaks down all carbohydrates. Forgetting to mention the enzyme‑substrate complex.
Mark scheme (5 marks)
- Amylase is a protein made from chains of amino acids
- Amylase has an active site with a specific/complementary shape
- Starch (the substrate) fits into the active site to form an enzyme-substrate complex
- Enzyme specificity means amylase will only act on starch / only one substrate fits the active site
- Amylase cannot break down other molecules (e.g. proteins/lipids) because their shape is not complementary to the active site
Key terms in this question
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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