# Denaturing

When heat or the wrong pH changes the shape of an enzyme so it can no longer work.

Biology (school) · Part 02: Moving materials, enzymes and energy · Card 5 of 11 · Last updated 2026-10-19

## Analogy

Like a key bent out of shape so it won't fit its lock.

## In practice

Most human enzymes denature above about 40 degrees Celsius, which is why a very high fever is dangerous.

## Practice

### Flashcards

- **Why does a denatured enzyme stop working?** Its shape has changed, so the substrate no longer fits the active site.

### Interview questions

**Describe how temperature affects the rate of an enzyme-controlled reaction.**

- Rate rises as temperature rises because particles collide more
- There is an optimum temperature where the rate is highest
- Above the optimum the enzyme denatures
- A denatured enzyme loses its shape and cannot work

## Questions people ask

### Can a denatured enzyme work again?

Usually not. Once heat or extreme pH has changed the active site's shape, it does not return to the original form, so the damage is permanent. This is different from cold, which only slows an enzyme down. Cooled enzymes recover when they warm up again.

### Why do different enzymes work at different pH values?

Each enzyme's shape is held together by chemical bonds that depend on pH. Pepsin works best in the strong acid of the stomach, about pH 2. Amylase works best in the mouth near pH 7. Put either in the wrong conditions and the shape changes and it denatures.

## Related concepts

- [Enzyme](https://studyvisually.com/learn/science/biology-school/biology-school-part-2/biology-school-part-2-concept-4)

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