Transcript Control of the Cell Cycle

Control of the Cell Cycle
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
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
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
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
Cancer
• Uncontrolled cell growth
• Cancer is a defect in cell cycle regulation
• Cancer can be traced to defects in
production and regulation of cyclins