Question

Regarding the mitotic cell cycle, what is meant by a checkpoint?

Answer 1

Cell cycle checkpoints are the cell surveillance mechanism by which cells are able to carry out the process of cell division successfully. Checkpoints monitor for the order of events, replication of DNA, and for the integrity of the cell cycle events. The events of the cell cycle which are monitored by the checkpoints are size and shape of the cells, intactness of DNA, and the accurate segregation of chromosomes in anaphase. For each event, there are different checkpoints.

There are mainly 3 checkpoint-

G1 checkpoints- It looks for whether a growth signal is present or not, nutrients are enough to complete the cell cycle, and DNA is not damaged. If any of the conditions are not fulfilled the cell cycle will get stopped and not proceed until all the conditions are appropriate.

G2 checkpoint- It prevents the cell to enter into the mitosis phase if DNA is damaged, it waits for the repair of DNA and if DNA damage is not repaired, it blocks the proliferation of DNA damaged cells.

Metaphase checkpoints or spindle assembly checkpoints- This checkpoint look for the attachment of microtubule to the kinetochore of each chromosome. It prevents the segregation of chromosomes if even the single chromosome kinetochore is not attached to the microtubule. This prevents the aneuploidy in cells.