Losing a cell cycle brake makes cells divide more
- The idea
- Predict
- See it
- Why
- Check
The idea
“If a checkpoint protein is lost, the cell can't get past the checkpoint and stops dividing.”
A checkpoint protein sounds like part of the division machine, so losing one sounds like a breakdown. Many are brakes, and without a brake the cell keeps going.
The short version
The mistake: If a checkpoint protein is lost, the cell can't get past the checkpoint and stops dividing.
What's actually true: Brakes like p53 halt the cycle and cyclin-CDKs drive it. Lose a brake and cells divide more. Lose a CDK and they divide less.
- Cyclins and the kinases they switch on, called CDKs, are accelerators that push a cell past a checkpoint. Brakes like p53 hold it there.
- Ask what the protein does when it works. Lose an accelerator and cells stall. Lose a brake and they go through even when they should wait.
- Accelerator genes are proto-oncogenes and brake genes are tumor suppressors. An overactive accelerator or a broken brake can both lead to cancer.
- Without its brake, a cell with damaged DNA doesn't pause. It copies the damaged DNA and passes the errors to both daughter cells.
On the exam: Lose a brake and cells divide more. Lose an accelerator and they divide less.