Explain why enzymes are described as biological catalysts and outline how an enzyme's structure is related to its function.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Enzymes are biological catalysts because they increase the rate of chemical reactions without being consumed, allowing them to be reused.
They are proteins composed of amino‑acid chains.
Each enzyme has a unique, three‑dimensional active site.
The substrate’s shape is complementary to this active site, so it fits precisely.
Binding of substrate to the active site forms an enzyme‑substrate complex, which lowers the activation energy and speeds the reaction.
They are proteins composed of amino‑acid chains.
Each enzyme has a unique, three‑dimensional active site.
The substrate’s shape is complementary to this active site, so it fits precisely.
Binding of substrate to the active site forms an enzyme‑substrate complex, which lowers the activation energy and speeds the reaction.
Examiner tips
- Use the word ‘catalyst’ and explain the rate‑increase and non‑consumption. Show the link between protein structure and a specific active site. Mention the complementary fit and enzyme‑substrate complex. Keep each point brief and to the point.
Common mistakes
- Confusing enzymes with other catalysts or saying they are used up. Forgetting to mention the protein nature of enzymes. Lacking the idea of the complementary fit or the enzyme‑substrate complex.
Mark scheme (5 marks)
- Enzymes speed up (the rate of) chemical reactions
- Enzymes are not used up / consumed in the reaction (so can be reused)
- Enzymes are proteins (made of amino acids / chains of amino acids)
- Each enzyme has a specific / uniquely shaped active site
- The substrate fits into the active site (because its shape is complementary to the active site) forming an enzyme-substrate complex
Key terms in this question
Related
- Revision notes: Proteins and Enzymes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Proteins and Enzymes questions
- Explain why increasing the concentration of an enzyme increases the rate of a re…
- Explain why enzymes are proteins and describe how the amino acid sequence of an …
- Explain how substrate concentration affects the rate of an enzyme-controlled rea…
- Explain why enzyme-controlled reactions have an optimum substrate concentration,…
- Explain why two different enzymes, such as amylase and lipase, can each only cat…
- Explain how temperature affects the rate of an enzyme-controlled reaction, inclu…