Question

When internal and external conditions are inappropriate to initiate a division cycle, the cells accumulate at the G1 restriction point. In animals, what protein is responsible for keeping cells at this restriction point?

Answer 1

The protein responsible for halting the cell cycle at the G1 restriction point in animal cells when conditions are not conducive for division is p53, which can trigger DNA repair or apoptosis to maintain genomic integrity.

Step-by-step explanation:

The G1 Checkpoint and Cell Cycle Regulation

In animal cells, the protein responsible for keeping cells at the G1 restriction point when conditions are inappropriate for division is p53. This protein acts as a quality control mechanism by inspecting the genomic DNA for damage. If DNA damage is detected, p53 responds by halting the cell cycle and initiating DNA repair through enzymes. Additionally, p53 can signal apoptosis to prevent the potential proliferation of damaged DNA. If the halt in the cycle is prolonged, p53 induces the production of p21, which further enforces the cell cycle arrest by inhibiting Cdk/cyclin complexes. This regulation ensures that only cells with intact DNA can proceed into the S phase and continue towards cell division.