A checkpoint pauses the cycle. Repair enzymes fix the DNA
- The idea
- Predict
- See it
- Why
- Check
The idea
“The checkpoint fixes damaged DNA, or keeps it from getting damaged.”
It's easy to picture a checkpoint as the fix for DNA damage. It's more like a stop light after a crash, holding traffic while someone else clears the road.
The short version
The mistake: The checkpoint fixes damaged DNA, or keeps it from getting damaged.
What's actually true: A checkpoint senses a problem and pauses the cycle. Other proteins repair the damage, or the cell is removed by apoptosis.
- A checkpoint is a control point in the cell cycle. Proteins check a condition, like intact DNA or chromosomes attached to the spindle, and signal stop or go.
- When DNA is damaged, checkpoint proteins block the cyclin-CDK activity that drives the cell into the next phase. The cycle pauses, often in G1 or G2.
- The repair itself is done by DNA repair enzymes while the cell waits.
- If the damage is too severe to repair, p53 and other checkpoint proteins can trigger apoptosis, or programmed cell death, so the damage isn't passed on.
On the exam: A checkpoint is a stop signal. Other proteins repair the damage, or the cell is removed.