1. Control of the Cell Cycle

2. Cyclins and the cell cycle
Cyclin was the name given to the protein that caused the spindle to form
First found in frogs
Injection of cyclin into a cell caused the cell to undergo mitosis
Cyclin is not only for making the spindle

3. Central role of cyclin
Cyclins are known now to regulate the timing of the cell cycle
Found in every eukaryotic cell (from yeast to human) that has been studied

4. Many different cyclins are known
Regulate different parts of the cell cycle
M phase cyclin controls the start of mitosis
G1 phase cyclin control the end of the gap 1 phase
S phase cyclin starts the synthesis phase
G2 phase cyclin regulates the gap 2 phase

5. Cyclin mechanisms
Cyclin protein is built at a constant rate until it reaches a critical point
Critical point initiates the next cyclin; previous cyclin is destroyed
Example:
when M phase cyclin reaches a critical point the cell divides;
when the cell goes into mitosis all M phase cyclin is destroyed, daughter cells start over again with no cyclin

6. Cancer Uncontrolled cell growth
Cancer is a defect in cell cycle regulation
Cancer can be traced to defects in production and regulation of cyclins