Biology › Section E · Cell communication and the cell cycle › Topic E.5
Control of the cell cycle
A cell that divides whenever it feels like it is a cancer cell in training. The cell cycle is policed at three checkpoints by external signals and internal molecules — positive regulators that push the cycle forward, and negative regulators that hold it back until every condition is met. The system is redundant, layered, and unforgiving, because the alternative is uncontrolled division.
In this topic
- Three gates on the road to division
- The G1 checkpoint: the point of commitment
- The G2 checkpoint: proofreading before mitosis
- The M checkpoint: all anchored before the pull
- Worked example: reading a 24-hour cycle budget
- Positive regulation: cyclins and Cdks
- Negative regulation: the brakes
- Worked example: a sunburned cell halts at G1
- Common mistakes to avoid
- Key takeaways
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