PATHOLOGY

Detailed explanation-1: -At the G1 checkpoint, cells decide whether or not to proceed with division based on factors such as: Cell size. Nutrients. Growth factors.

Detailed explanation-2: -The restriction checkpoint is influenced primarily by growth factors, cell size, cell nutrition, and DNA damage (2, 5). The DNA replication checkpoint is primarily influenced by improper DNA replication and damage, and the metaphase/ anaphase checkpoint is influenced by chromosome attachment to the mitotic spindle (1).

Detailed explanation-3: -The G1/S checkpoint prevents cells from entering the S phase in the presence of the DNA damage by inhibiting the initiation of replication.

Detailed explanation-4: -The most well-known mechanism for DNA damaged-induced G1 arrest is that mediated by the tumor-suppressor protein p53 in mammalian cells. DNA damage stabilizes the p53 protein and activates its transcription function. One of the p53 target genes is p21Cip1, a heat-stable inhibitor of Cdk/cyclin.