Cyclin is the regulatory molecule which bind to the cyclin
dependent protein kinase and allow the cdk to phosphorylate the
target protein. Rise and fall in the concentration of the cyclin is
responsible for the activation of the cdk molecule.
Phosphorylation of the threonine residues at 161 position of
the cdk by cdk activating kinase( CAK) . This phosphorylation
result in the conformation changes which increases the efficiency
of the cdk to phosphorylate the protein effectively.
Cdk molecule are also regulated by the binding of cdk
inhibitor. Binding of inhibitor to cdk prevent the cell cycle
progression.
Cdk subunit get inhibited when tyrosine residues at 15 position
get phosphorylated . Because of this cdk get inactivated . Cdc25
phosphatase remove the phosphate at 15 position and result in
activation of CDK.