What is the purpose of the G2 checkpoint?

The G2 checkpoint is often referred to as the G2-M checkpoint because it is located at the boundary between the G2 phase and the M phase (mitosis) of the cell cycle. This checkpoint plays a key role in deciding whether the cell is ready to move from G2 phase into mitosis. The name "G2-M" itself reflects its position and function, it lies at the end of the G2 phase but directly regulates the cell's entry into the M phase.

During the G2 phase, the cell completes the synthesis of proteins and prepares all necessary components for mitosis. However, before entering mitosis, the cell must ensure that the DNA, which was replicated during the S phase, is completely and correctly duplicated and that there is no DNA damage. At this critical point, the G2-M checkpoint becomes active. It functions like a gatekeeper or quality control system. It checks:
  • Whether DNA replication has been completed without any errors
  • Whether the DNA is free of any damage
  • Whether the cell has all resources and proteins necessary to undergo mitosis
This checkpoint prevents the cell from prematurely entering mitosis. If any issues are found, such as incomplete replication or DNA damage, then the checkpoint halts the progression of the cell cycle. This delay provides time for repair mechanisms to fix the issues. If the damage is not repairable, the cell may undergo apoptosis, which is a programmed cell death process, to prevent the division of cells with defective genetic material.

This whole process is regulated by several important proteins. ATM (Ataxia Telangiectasia Mutated) and ATR (ATM and Rad3-related) are two proteins that detect DNA damage. When damage is detected, they activate Chk1 and Chk2 kinases. These kinases then stop the function of Cdc25 phosphatase, which is needed to activate Cyclin B-CDK1 complex. Without this complex, the cell cannot enter mitosis. This is how the checkpoint ensures that the cell cycle only continues when it is safe to do so.

Thus, the checkpoint is crucial for maintaining genomic integrity, and it is referred to as the G2-M checkpoint because this checkpoint lies between G2 and M phases and controls the transition between them, scientists call it the G2-M checkpoint rather than just the G2 checkpoint.





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