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A checkpoint in the cell cycle is a control point where regulatory proteins assess if certain conditions are met before allowing progression to continue. One important checkpoint ensures accurate replication of DNA before entering mitosis.
The G1 checkpoint verifies if conditions are favorable for cell division, such as sufficient nutrients and DNA integrity.
The S phase is the stage of interphase where DNA replication occurs.
The G2 checkpoint ensures that DNA replication has been completed accurately and that the cell is ready for mitosis.