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The Regulation of Cell Cycle
The cell cycle is under the control of various cdks and Cyclins.These control the cell cycle progression to varoius phases of cell cycle.
Here I am dealing with the G or growth phase and M.or mitotic Phase.
The cell cycle is divided into four phases
1. G0 Phase and G1
2. S or synthesis phase wherein synthesis of DNA takes place
3 G2 Phase
4. M or mitotic Phase.
There are check points in the cell cycle which requires CDK-cyclin activity to pass them.
One check point at G1 phase. To pass this CDK4&6 and cyclin D is required.
Another check point is at G1-S transition this require CDK2 and cyclin E.
CDK2 and Cyclin E is also required for initiation of DNA replication and chromosome replication.
For progression through S phase CDK2 and cyclin A is required.
Another check point is at S-G2 transition which requires CDK 1 and cyclinA.
For G2 - M transition CDK 1 and cyclin B are required.
Some mechanism regulate CDKs.
Several inhibitors bind to CDK at specific sites for its activation and deactivation.
1. Ink 4 family of protein: These protein are prominent for CDK 4& 6. when they bind to them they stop cell cycle from G1-S progression and the cell will remain in G1 phase.
2. Cip/Kip Family of proteins: Act on CDK 2 and can also bind to cyclin A and E and stop cell cycle in S or G1 phase. These also hep in association of CDK 4& 6 with cyclinD and in G2 M transition phase it also enhance association of CDK 1 with cyclin B.
All external factors such as erk, ras, Raf, MEK signal the cell externally for cell division and these finaly led to the formation of cyclin D.
Cyclin D is only  synthesised as long as external signals are available.
Cyclin D mutation also led to several cancer.


Hope this will help you all. See you all in next blog.
Thnkyou for reading.