Understanding:
1.6.U5: Cyclins are involved in the control of the cell cycle.
Objectives:
1.6.U5: Cyclins are involved in the control of the cell cycle.
Objectives:
- Explain the role of cyclin and cyclin-CDK complexes in controlling the cell cycle.
- State the role of cyclins D, B, A and E in the cell cycle.
Cyclins are a family of regulatory proteins that control the progression of the cell cycle. Cyclins activate cyclin dependent kinases (CDKs), which control cell cycle processes through phosphorylation.
When a cyclin and CDK form a complex, the complex will bind to a target protein and modify it via phosphorylation. The phosphorylated target protein will trigger some specific event within the cell cycle (e.g. centrosome duplication, etc.). After the event has occurred, the cyclin is degraded and the CDK is rendered inactive again.
When a cyclin and CDK form a complex, the complex will bind to a target protein and modify it via phosphorylation. The phosphorylated target protein will trigger some specific event within the cell cycle (e.g. centrosome duplication, etc.). After the event has occurred, the cyclin is degraded and the CDK is rendered inactive again.
There are 4 main types of cyclin in human cells.
Cyclin D – causes G0 to move to G1 and G1 to move to S phase
Cyclin E – causes the cell to prepare for replication in S phase
Cyclin A – activates DNA replication in S phase
Cyclin B – causes the mitotic spindle to begin to form and other tasks needed in the preparation of mitosis
Cyclin Expression Patterns
Cyclin concentrations need to be tightly regulated in order to ensure the cell cycle progresses in a proper sequence. Different cyclins specifically bind to, and activate, different classes of cyclin dependent kinases
Cyclin levels will peak when their target protein is required for function and remain at lower levels at all other time