Cell cycle checkpoint
A control point where the cell checks that conditions are right before moving on. Main checkpoints: G1 (size, nutrients, DNA damage), G2 (DNA fully copied) and M (chromosomes attached to the spindle). Cyclins and CDK enzymes drive the cycle.
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Analogy
Airport security gates: no pass, no boarding.
In practice
The protein p53 stops the cycle at G1 if DNA is damaged, giving time for repair or triggering cell death.
Practice
Flashcards
- Name the three main cell cycle checkpoints.G1, G2 and the metaphase (spindle) checkpoint.
Interview questions
- Explain how checkpoints control the cell cycle and what happens when the control fails.
- Checkpoints at G1, G2 and M
- Cyclins and CDKs drive progress
- p53 stops damaged cells
- Mutation in brakes or accelerators leads to cancer
Questions people ask
What are cyclins?
Cyclins are proteins whose levels rise and fall through the cell cycle. A cyclin binds to a cyclin-dependent kinase (CDK), an enzyme that is always present, and switches it on. The active pair adds phosphate groups to target proteins, which triggers the next stage of the cycle.
What is apoptosis?
Apoptosis is programmed cell death, a tidy process in which the cell shrinks, breaks its DNA and is cleared away. It removes damaged cells and shapes the body, for instance by removing the webbing between fingers in a developing embryo. Failure of apoptosis can contribute to cancer.