# Enzyme

A protein (sometimes RNA) that speeds up a reaction by lowering its activation energy. It is not used up and does not change delta G.

Biology (university) · Part 02: Enzymes and energy · Card 5 of 9 · Last updated 2026-10-19

## Analogy

A tunnel through a mountain: same start and end, much easier route.

## In practice

Amylase in saliva breaks starch into sugars. Without enzymes, many reactions in the body would take years.

## Practice

### Flashcards

- **How do enzymes speed up reactions?** They lower the activation energy. They do not change delta G or get used up.

### Interview questions

**Explain how an enzyme speeds up a reaction without changing the free energy change of that reaction.**

- Lowers activation energy
- Stabilises the transition state
- Does not change start or end energy levels
- Is not consumed

## Questions people ask

### Why are enzymes so specific?

The active site has a particular shape and pattern of charges, which fits only certain substrates, like a lock fits certain keys. This lets each enzyme control one reaction, or a closely related few. Cells can therefore switch individual reactions on or off without disturbing others.

### What happens to an enzyme at high temperature?

As temperature rises, reactions speed up until the enzyme begins to denature. Heat breaks the weak bonds that hold the protein in its shape, the active site distorts, and activity drops sharply. Most human enzymes work best near 37 degrees Celsius and stop working above about 50.

## Related concepts

- [Free energy](https://studyvisually.com/learn/science/biology-university/biology-university-part-2/biology-university-part-2-concept-3)
- [Active site and induced fit](https://studyvisually.com/learn/science/biology-university/biology-university-part-2/biology-university-part-2-concept-6)
- [Enzyme kinetics](https://studyvisually.com/learn/science/biology-university/biology-university-part-2/biology-university-part-2-concept-7)
- [Enzyme inhibition](https://studyvisually.com/learn/science/biology-university/biology-university-part-2/biology-university-part-2-concept-8)

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