IB Biology Topic D2.1 Cell and Nuclear Division…

Cyclins: The Proteins That Drive The Cell Cycle Forward

The cell cycle must be tightly controlled so each stage happens in the right order and only when the cell is ready.
Cyclins are regulatory proteins that control this progression by switching on enzymes called cyclin-dependent kinases (CDKs).
Different cyclins are made at different times, so each one triggers a specific phase of the cell cycle.
The phases themselves (G1, S, G2 and M) are covered in D2.1.13, so here the focus is on how cyclins control the move from one phase to the next.

Definition

Cyclins

A group of proteins that regulate the cell cycle by activating cyclin-dependent kinases (CDKs).

A cyclin binds to a CDK to form an active cyclin-CDK complex.
1. A CDK on its own is inactive, so it only works once a cyclin is bound to it.

The cell cycle must be tightly controlled so each stage happens in the right order and only when the cell is ready.
Cyclins are regulatory proteins that control this progression by switching on enzymes called cyclin-dependent kinases (CDKs).
Different cyclins are made at different times, so each one triggers a specific phase of the cell cycle.
The phases themselves (G1, S, G2 and M) are covered in D2.1.13, so here the focus is on how cyclins control the move from one phase to the next.

Definition

Cyclins

A group of proteins that regulate the cell cycle by activating cyclin-dependent kinases (CDKs).

A cyclin binds to a CDK to form an active cyclin-CDK complex.
1. A CDK on its own is inactive, so it only works once a cyclin is bound to it.