# Explain how the induced fit model of enzyme action differs from the lock-and-key model, and why induced fit better accounts for the catalytic activity of enzymes.

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

## Mark scheme (4 marks)

1. In the lock-and-key model, the active site is rigid/fixed in shape and the substrate fits exactly without any conformational change.
2. In the induced fit model, the active site changes shape / undergoes a conformational change as the substrate binds, so the enzyme moulds around the substrate.
3. The conformational change in induced fit places catalytic residues/amino acid R-groups in the correct orientation/position to facilitate the reaction / to strain or distort the substrate's bonds.
4. Induced fit better accounts for catalysis because a perfectly rigid complementary fit (lock-and-key) would stabilise the substrate rather than destabilise / strain its bonds, so a static active site would not lower activation energy effectively.

## Key terms

- [induced fit model](https://www.gradenine.co.uk/glossary/induced-fit-model)
- [lock-and-key model](https://www.gradenine.co.uk/glossary/lock-and-key-model)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-induced-fit-model-77001bfb) · Published by Druglandscape Ltd.