A tumor suppressor is a brake, and cancer loses it
- The idea
- Predict
- See it
- Why
- Check
The idea
“A mutated tumor suppressor starts pushing the cell to divide, like an oncogene.”
Both end with a cell dividing too much, so they blur together. A lost brake and a stuck accelerator fail differently.
The short version
The mistake: A mutated tumor suppressor starts pushing the cell to divide, like an oncogene.
What's actually true: Tumor suppressor mutations remove a brake and usually need both copies. Oncogene mutations add a push and need only one.
- Proto-oncogenes, like ras, make proteins that push the cycle forward. A mutation that makes the protein overactive turns it into an oncogene.
- Tumor suppressor genes, like p53 and Rb, make proteins that hold the cycle at checkpoints. Losing them helps cause cancer, and usually both copies must go.
- A lost brake adds no push. Putting back a working copy restores the brake, but it can't calm an overactive accelerator.
On the exam: An oncogene is a stuck accelerator. One copy is enough. A tumor suppressor is a brake. Both copies must go.