Cyclins Regulate The Cell Cycle
- The cell cycle must be tightly controlled to ensure processes occur in the correct order.
- Cyclins are regulatory proteins that control progression through the cell cycle by activating enzymes called cyclin-dependent kinases (CDKs).
- Different cyclins are specific to different phases of the cell cycle.
Definition
Cyclins
A group of proteins that regulate the cell cycle by activating cyclin-dependent kinases (CDKs).
How Cyclins Work
- Cyclins bind to CDKs, forming an active complex.
- This complex phosphorylates target proteins, activating them to perform tasks specific to the cell cycle phase.
- Cyclin levels rise and fall in a predictable pattern, ensuring precise control.
- Don’t confuse cyclins with CDKs.
- Cyclins are the proteins that regulate the cycle, while CDKs are the enzymes they activate.
Cyclin Levels and Checkpoints
- The cell cycle contains checkpoints, control points where the cell verifies that conditions are suitable to proceed.
- To pass each checkpoint, a threshold level of a specific cyclin must be reached.
- If cyclin concentration is too low, the cell pauses at the checkpoint until conditions are met.
- Once the cyclin reaches threshold levels, the cell advances to the next phase.
- After the checkpoint is passed, cyclin levels decrease, preventing the cell from re-entering that phase prematurely.
- Cyclins act as molecular timers.
- Their rising and falling concentrations ensure that cell cycle events happen in the correct sequence and only when the cell is ready.
Explain how cyclin concentration controls progression through cell cycle checkpoints.
