Cell cycle checkpoint p53

The cell cycle is a has many components that allow it to function properly and ensure that the cell ready to replicate and does so in a safe manner. This means that the cell needs a way to check that everything is accounted for, there has been no errors in DNA replication and the spindles during mitosis are aligned properly. For these reasons, the cell cycle has checkpoints that make sure the important processes of the various stages of the cell cycle have finished and been completed correctly before moving on to the next stage of the cycle. These checkpoints have the ability to put a hold on the cell cycle if more time is needed for the cell to catch up and is done so through the control of CDK. The stages of the cell cycle have various proteins that are capable of deactivating CDK directly or activate CDK inhibitor proteins. One of the most important checkpoint proteins in the cell cycle is p53. Described as the “guardian of the genome”, p53 is activated in cells in response to DNA damage. The transcription factor p53 activates upon the detection of DNA damage and activates the transcription of p21, which serves as a CDK inhibitor. The transcription factor is carefully controlled through posttranslational modification. In the absence of DNA damage, p53 is degraded by proteasomes, but in the presence of damage it is phosphorylated to a stable and activated state. The inhibition of G1/S CDK and S CDK by p21 is necessary to stop the cell cycle before DNA replication occurs in the S-phase of the cell cycle so that the DNA damage is not replicated in the new strand and passed along to the new cell.