# Explain how the structure of an enzyme's active site determines its specificity for a particular substrate.

> IB DP Biology Standard Level (2023 syllabus) — C1.1 Enzymes and metabolism · Explain · 4 marks

## Mark scheme (4 marks)

1. The active site has a specific/complementary shape (tertiary structure) that matches only one substrate or a small group of structurally similar substrates.
2. The amino acid residues lining the active site form non-covalent interactions (e.g. hydrogen bonds, ionic interactions, van der Waals forces) with specific chemical groups on the substrate.
3. If a molecule lacks the correct shape or chemical groups it cannot bind to the active site, so the enzyme will not catalyse a reaction with that molecule / substrate specificity is a result of this selective binding.
4. The induced-fit model describes how the active site can change shape slightly upon substrate binding to optimise the fit, further ensuring specificity and lowering the activation energy of the reaction.

## Key terms

- [active site](https://www.gradenine.co.uk/glossary/active-site)

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-an-5ba28641) · Published by Druglandscape Ltd.