Final answer:
The three major checkpoints during the cell cycle are the G1 checkpoint, which ensures that the cellular conditions are right for division; the S checkpoint, which confirms proper DNA replication; and the mitotic spindle checkpoint, which verifies correct chromosome alignment before cell division.
Step-by-step explanation:
In cell biology, there are three major checkpoints during the cell cycle that determine whether a cell will divide. These checkpoints ensure that cells divide correctly and that their DNA is intact and accurately replicated.
The G1 Checkpoint
The G1 checkpoint, also known as the restriction point, occurs just before the cell enters the S phase. This checkpoint assesses whether the cell is of adequate size, has sufficient nutrients, and has undamaged DNA. If any of these conditions are not met, the cell may enter a resting state (G0) or attempt to repair the issues before proceeding.
The S Phase Checkpoint
During the S phase, the cell undergoes DNA replication. The S checkpoint is in place to ensure that DNA has been replicated properly. Any errors in DNA replication must be corrected before the cell can continue to the next phase.
The Mitotic Spindle Checkpoint
The mitotic spindle checkpoint occurs during metaphase of mitosis, where it checks that all chromosomes are properly aligned at the mitotic plate and that each kinetochore is correctly attached to a spindle fiber. Only after this condition is met, the cell is allowed to proceed to anaphase and complete cell division.