Final answer:
P53 stops the cell cycle at the G1 checkpoint to either allow damaged DNA repair or to initiate apoptosis. It also activates genes for DNA repair and controls the apoptosis process. P53 is essential for maintaining cellular integrity and preventing cancer growth.
Step-by-step explanation:
P53 and Cell Cycle Arrest
The protein p53 functions as a crucial checkpoint in cellular regulation, primarily acting at the G1 checkpoint of the cell cycle. When the presence of damaged DNA is detected during the G1 phase, p53 halts the cell cycle to facilitate either repair of the DNA or to trigger apoptosis if repair is not possible. Furthermore, p53 enforces the cell cycle arrest through increasing levels of p21, which inhibits the activity of Cdk/cyclin complexes that are necessary for the cell to transition into the S phase.
In addition to controlling the cell cycle, p53 is also responsible for activating genes involved in DNA repair and can initiate programmed cell death, also known as apoptosis, to prevent the propagation of cells with irreparable damage.
The role of p53 is so pivotal in maintaining cellular integrity that it is often referred to as "the Guardian of the Genome." This protein's multifunctional nature is crucial for the suppression of tumorigenesis, thus underlining its importance in the prevention of cancer.