# Explain how the cell cycle is regulated to prevent uncontrolled cell division, with reference to cyclins and tumour suppressor genes.

> IB DP Biology Higher Level (2023 syllabus) — D2.1 Cell and nuclear division · Explain · 4 marks

## Mark scheme (4 marks)

1. Cyclins accumulate and then are degraded at specific points in the cell cycle, controlling progression through checkpoints.
2. Cyclins bind to and activate cyclin-dependent kinases (CDKs), which phosphorylate target proteins to drive the cell cycle forward.
3. Tumour suppressor genes (e.g. p53 or Rb) encode proteins that inhibit cell cycle progression or promote apoptosis when DNA damage is detected.
4. Loss-of-function mutations in tumour suppressor genes remove these inhibitory controls, allowing unregulated division and potentially leading to cancer/tumour formation.

## Key terms

- [cyclin](https://www.gradenine.co.uk/glossary/cyclin)
- [tumour suppressor gene](https://www.gradenine.co.uk/glossary/tumour-suppressor-gene)

## 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-cell-cycle-is-ad9f6740) · Published by Druglandscape Ltd.