---
title: "Cell Cycle Checkpoints, Control and Cancer"
description: "Checkpoints hold a cell back at set points in the cycle until conditions and DNA are sound. Tumours follow when the genes that run those checkpoints stop working."
canonical: https://lightmysky.com/learn/science/cell-cycle-checkpoints-control-and-cancer-mt_nwNmCVnZ7O
source: https://lightmysky.com/learn/science/cell-cycle-checkpoints-control-and-cancer-mt_nwNmCVnZ7O.md
retrieved: 2026-09-12
---

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# Cell Cycle Checkpoints, Control and Cancer

Checkpoints hold a cell back at set points in the cycle until conditions and DNA are sound. Tumours follow when the genes that run those checkpoints stop working.

Subject: Science · Area: Organisms & Life Processes · Ages 17 to 18
Page: https://lightmysky.com/learn/science/cell-cycle-checkpoints-control-and-cancer-mt_nwNmCVnZ7O

## Ready when they can

- Names what each checkpoint is testing before the cell is allowed on.
- Distinguishes a gene that drives division from one that holds it back.
- Links a mutation in a control gene to uncontrolled division rather than to a faulty protein in general.

## Lesson: Checkpoints that guard cell division

Your cells carry built in stop signs called checkpoints, and a cell may only pass when each test is satisfied. Skip enough of these tests and a tumour can start, which is why the checkpoints matter. The G1 checkpoint asks whether the cell is big enough and its DNA is undamaged. The G2 checkpoint asks whether DNA was copied fully and correctly. The spindle checkpoint, during mitosis, asks whether every chromosome is attached before they are pulled apart.

Signals from cyclins and kinases switch each stage on or off, and every border works like a locked gate. If a test fails, the cycle halts while repairs happen. If the damage is too severe to fix, the cell is ordered to die instead. That strict gating is why healthy tissue grows in an orderly way.

Two gene families run the gates from opposite sides. Proto-oncogenes encourage division only when it is needed, like an accelerator pressed at the right moment. Tumour suppressor genes hold division back, like brakes. Keep the two apart: one drives, the other restrains.

**Example.** Cancer is division with the controls broken. A mutation can lock a proto-oncogene permanently on, like an accelerator stuck down, or knock out a tumour suppressor gene, like cut brakes. Either fault lets cells race past checkpoints and form a tumour. Most tumours need several such mutations stacked over years, not one single error.

**Recap.** Checkpoints halt the cycle until each test passes, and broken control genes let cells divide without limit.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [The Cell Cycle and Mitosis](https://lightmysky.com/learn/science/the-cell-cycle-and-mitosis-mt_gllZOZEzW7)

## Opens up

- [Fertilisation and the First Cleavages](https://lightmysky.com/learn/science/fertilisation-and-the-first-cleavages-mt_9BXQsdP8fI)
- [Apoptosis: Caspase Cascades and the Decision to Die](https://lightmysky.com/learn/science/apoptosis-caspase-cascades-and-the-decision-to-die-mt_Pi6c9yoT7w)