Much of the work has been informed by study of simple organisms, such as yeast.
Phases: G1 (->G0) S-phase (synthesis) G2 M-phase (mitosis)
Much of the cell cycle is regulated by kinases, protein enzymes that add phosphate groups to other proteins, resulting in a change to their enzymatic activity. The proteins relevant to cell replication and division are activated by a carefully controlled sequence of events.
The specific kinases involved in this process are cyclin-dependent kinases (CDK), which as the name suggests, require a partner cyclin component to function. The resulting protein complex resulting requires further activation through phosphorylation of a specific threonine residue. This is achieved, in turn, by a CDK activating kinase (CAK), a function which may be provided by a different cyclin-CDK complex, allowing a network of various checks and balances. The activity of the resulting complex can be modulated by
- further phosphorylation at other amino acid sites (reversible)
- binding with CDK inhibitors (reversible)
- degradation of the cyclin sub-unit (irreversible until further cyclin produced)