What conditions need to be met in order for a cell to pass the critical checkpoint the G1 stage?
1 Answer
Cell size, DNA integrity and availability of nutrients and building blocks.
Explanation:
There are several checkpoints in the cell cycle (see image). These are important moments in which a cell decides whether it will continue with the cell cycle or not.
The checkpoint of the G1 (Gap 1) phase is located at the transition between G1 and S-phase. At this point the cell decides if it is ready to start the process of DNA duplication (S-phase).
This is a critical checkpoint, because once the cell has passed, it is committed to division, there is no way back. When another problem is encountered at other checkpoints, the cell will usually kill itself (apoptosis).
Because there is no way back, the cell checks whether internal and external conditions are favorable for division. This includes:
- Cell size : is the cell large enough to contain the two sets of DNA in S-phase? (growth further occurs during G2-phase and is checked again there).
- Nutrients: are there enough nutrients to provide energy for the cell?
- Building blocks: are there enough building blocks (nucleotides) to make DNA in S-phase?
- DNA integrity: is the DNA undamaged and therefore suitable for copying in S-phase?
Once all the boxes are checked the cell is ready. It will also need signals from the environment / neighboring cells to be sure that it is allowed to start division.
