Biology / Unit 4: Cell Growth and Division
4.3 Regulating the Cell Cycle and Cancer
Notes
Cells control when they divide using checkpoints and regulatory proteins.
- Checkpoints (in G1, G2 and during mitosis) check for DNA damage and correct chromosome attachment before moving on.
- Cyclins are proteins that help drive the cycle forward.
- Growth factors signal cells to divide; normal cells stop dividing when crowded (contact inhibition).
- Cancer is uncontrolled cell division, usually caused by mutations in genes that control the cycle.
- A mass of extra cells is a tumor. Malignant tumors invade nearby tissue and can spread (metastasis); benign tumors stay in place.
- Risk factors include UV light, tobacco smoke and some viruses.
Practice
What is the main cause of cancer at the cellular level?
Damaged control genes let cells divide without stopping.
Normal cells in a dish stop dividing when they touch each other, but cancer cells pile up. The cancer cells have lost:
Contact inhibition stops normal cells from dividing when crowded.
A tumor whose cells break off and travel to other parts of the body is described as:
Malignant tumors invade and spread through metastasis.
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