Checkpoints in the Cell Cycle MCQ - Practice Questions with Answers

Control and Regulation of the Cell Cycle

• The regulation of the cell cycle is important so that faulty or compromised cell could not divide.
• There can be a mutation during DNA replication and other events of the cell cycle.
• Therefore, there are checkpoints in the cell cycle that would check for the errors and would stop the cell cycle if there is any fault and would allow the cell cycle to continue if there is no fault.
• There are three checkpoints in the cell cycle as G1 checkpoint, G2 checkpoint and M checkpoint.

 G1 checkpoint:

• The G1 checkpoint determines whether all conditions are favourable for cell division to proceed.
• If this checkpoint is crossed, then the cell is irreversibly committed for the cell division.
• This checkpoint checks for adequate reserves, cell size and genomic DNA damage.
• A cell that does not meet all the requirements will not be allowed to progress into the S phase.

G2 checkpoint:

• The G2 checkpoint prevents entry into the mitotic phase if certain conditions are not met by the cell.
• At this checkpoint, cell size and protein reserves are checked.
• The most important checking at the G2 checkpoint is to check whether all the chromosomes have been replicated and that the replicated DNA is not damaged.
• If the problem is detected, then the cell cycle is halted.
• The cell attempts to either complete DNA replication or repair the damaged DNA.

M checkpoint:

• The M checkpoint occurs near the end of the metaphase stage of karyokinesis
• It checks whether all the sister chromatids are correctly attached to the spindle fibres.

Proteins involved in the regulation of cell cycle:

• Two groups of proteins called cyclins and cyclin-dependent kinases (Cdks) are responsible for the progress of the cell through the various checkpoints.
• There are four cyclins and four Cdks. 
• After the cell moves to the next stage of the cell cycle, the cyclins that were active in the previous stage are degraded.