P53 is a tumor suppressor gene, and some scientists refer to it as "the guardian of the genome."

a) explain its normal role and why scientists would regard it as the "guardian of the genome."
b) explain what happens to the cell cycle, if both p53 alleles are mutated.

P53 protein is a tumor supressor protein.p53 is so named because it has a molecular weight of 53 kd.p53 is encoded by TP53 gene.p53 is called the guardian of the genome because it helps to maintain balance between live cells and dead cells.

Explanation:

p53 is an important regulatory protein of apoptosis or programmed cell death.p53 helps in the destruction of damaged cells or cell with damaged DNA thus ensuring that every cell in our body has normal DNA.

   Mutation of p53 result in the generation of cancer because p53 is a potent regulator of cell cycle.

  p53 destroy the damaged cells by activating p21 which in turn blocks G1 cyclin CDK  thus blocking the cell to enter the S phase or synthesis phase.

 Mutation in p53 result in the progression of abnormal cell through the cell cycle which ultimately result in formation of abnormal protein thus giving rise to the onset of cancer.

the endomembrane system i think