Question

What is the major machinery that decides whether a cell progresses through the G1 checkpoint, and how dos theis machinery implement these decisions?

Answer 1

from G1 to S checkpoints-

1) size of cell- cell has to big in size.

2) enough amount of nutrient is present.

3) got some positive signals to divide from neighbouring cells.

4) DNA integrity- whether the DNA has any damage or not.

during G1 to S phase transition transcription factor RB binds to E2F and inhibit the synthesis of S phase gene transcription. when RB is phosphorylated with cyclin CDK complex it will no longer be associated with E2F factor and E2F will start the synthesis of S phase gene transcription. p21, p27 and p57 binds with cyclin CDK complex and inactivates it.