Rucete ✏ Biology In a Nutshell
1. Checkpoints in the Cell Cycle
- Checkpoints monitor and regulate the cell cycle.
- Major checkpoints include:
- G1 checkpoint: Checks for cell size, nutrients, and DNA damage.
- G2 checkpoint: Ensures DNA replication is complete and error-free.
- M checkpoint: Confirms that all chromosomes are properly attached to the spindle.
2. Cyclin and Cyclin-Dependent Kinases (Cdks)
- Cyclins are regulatory proteins that fluctuate in concentration during the cell cycle.
- Cdks (cyclin-dependent kinases) are enzymes that, when bound to cyclins, activate or inactivate other proteins by phosphorylation, driving the cell cycle forward.
3. Growth Factors
- External signals that promote cell division.
- Example: Platelet-derived growth factor (PDGF) stimulates cell growth and division in response to injury.
4. Density-Dependent Inhibition
- Cells stop dividing when they become too crowded.
- This prevents overgrowth in tissues.
5. Anchorage Dependence
- Most cells must be attached to a surface (like the extracellular matrix or a flat surface) to divide.
- Ensures cells grow only in proper locations.
6. Cancer and Loss of Control
- Cancer cells ignore the normal signals of cell cycle regulation.
- They can divide without growth factors, ignore density-dependent inhibition, and do not require anchorage—leading to uncontrolled growth and tumor formation.
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Biology in a nutshell