How the Cell Cycle is Regulated
- The cell cycle is a sequence of stages including interphase (G1, S & G), mitosis (M) and cytokinesis (C)
- There are three checkpoints in the cell cycle which must be overridden before the next stage can begin
- These checkpoints are located at G1, G2 and M
- The cycle is controlled by cyclins (a group of proteins) and kinases (enzymes)
- There are four different cyclins (D, E, A & B) whose concentrations rise and fall over the cycle:
- Each of these will trigger specific events in the cell cycle to occur
Cyclin control of the cell cycle diagram
Cyclins control the cell cycle. The presence of certain cyclins triggers a specific stage of the cell cycle.
- When each of the different cyclins reach a certain concentration (or threshold level) they trigger the next stage of the cell cycle
- This ensures key processes (e.g. DNA replication, organelle multiplication and protein synthesis) occur at the correct time
- When a specific cyclin has reached a certain concentration it will bind with another group of proteins (cyclin-dependent kinases) forming a complex which is activated
- This complex phosphorylates (attaches a phosphate) a target protein which activates it, causing it to trigger specific functions (e.g. DNA replication)
- Once the specific function is complete the phosphate is released, the cyclin breaks down and the cyclin-dependent kinases become inactive
Mechanism of cyclin action diagram
The mechanism for the cell cycle control by cyclins
Exam Tip
Note that you are not required to know details of the roles of specific cyclins for the AP Exam.