Cylin dependent kinases
Cyclin Dependent Kinases (Cdk) are enzymes associated with different checkpoints within the eukaryotic cell cycle. They belong to the family of enzymes; kinases, and work by phosphorylating proteins thus, activating or deactivating other protiens or pathways within the cell. Cyclin dependent kinases as the name suggests are dependent on a protein called cyclin, which at differing periods within the cell cycle is readily available to bind to Cdk's forming cyclin- Cdk complexes. Cdk's high affinity binding of the Cdk and the cyclin protein activates the enzyme activity within the kinase. One specific Cdk can engage with multiple cyclins at multiple times in the cell cycle permitting them to various tasks However this is unique to unicellular eukaryotes like yeast. The Cdk's occur at checkpoints within the cell cycle as I mentioned earlier, these checkpoints occur at the end of the G1 phase throughout the S phase and on entry to the M phase . An example of a checkpoint is the B-Cdc2 complex found in mammals and determines whether the cell enters the M phase (mitosis) from the G2 phase. These checkpoints act as a window of choice within the cell cycle where by the cell can either continue on to the next stage, enter a stage of quiesence called G0 or induce the nessecary mechanisms for programmed cell death, or apoptosis.