Cell Cycle Control System

Regulation of the cell cycle is a crucial process to the survival of the cell. Cell regulation includes the detection and repair of genetic damage and also prevention of uncontrolled cell division. The molecular events that control the cell cycle occurs in a sequential fashion and is impossible to reverse the cycle. 

The major event in the cell cycle is the replication of DNA, which occurs in the S phase, and separation of the duplicated chromosomes and the constituents of the cell which occurs in the M phase. Regulation and the initiation and completion of S and M phases ensures the genetic information and other cellular components are duplicated and divided equally between the daughter cells with each cycle.  

Cell cycle checkpoints are the regulatory pathways that control the order and the timing of the transitions of the cell cycle. The checkpoints also ensures that critical events such as replication of DNA and segregation of chromosomes are completed before the cell progresses further through the cycle. The cell-cycle checkpoints respond to the cellular damage by slowing the cycle to provide time for repair and it also induces transcription of genes that facilitate the repair. The loss of the checkpoints results in instability of chromosomes and it can result in the transformation of normal cells into cancer cells.

 

Proteins like the cyclin dpendent kinase, kinases and cyclins control the switches for the cell cycle causing the cell to move from G1 to S or G2 to M.Regulatory molecules are of two classes cyclins and cyclin-dependent kinases. The genes encoding cyclins and CDKs are conserved among all eukaryotes. Proteins like the p27 and p53 prevent the cells from passing check points. They are also knwon as protein suppressors. P27 protein binds to cyclin and CDK blocking the entry into the S phase. P53 protein blocks the cell cycle at the M checkpoint if the DNA is damaged. P53 mutation is the most frequent mutation found in cancer cells. P53 fucntions by blocking the cycle giving the cell time to repair its DNA. If there is severe damage in the DNA the protein causes the cell to apoptosis.