What is the role of P53 in Cell Cycle Check Point?

Answer 1

The p53 Tumour suppressor gene is located on chromosome 17. As its name suggests, it has an anti-tumour activity. That involves the overseeing of the cell cycle. If either the cell or the DNA is impaired, p53 activates the production of specific chemicals (like p21 protein), which interferes with the cell cycle. Depending on the nature/extent of the damage, its either repaired, thus cell cycle is allowed to continue, or p53 initiate apoptosis (cell death).

This mechanism would effectively stop the proliferation of infected (malignant) cells, however, p53 itself (or any of genes/chemicals p53 regulates) could be damaged/mutated. In the inherited condition, Li-Fraumeni syndrome, for example, only one functional copy of p53 gene is inherited (instead of two), which interferes with its normal function.