Which of the following cell cycle checkpoints is extremely important in preventing cells from dividing prematurely, thereby maintaining proper timing of cell division?

• A. The G2/M checkpoint
• B. The G1/S checkpoint
• C. The cytokinesis checkpoint
• D. The metaphase/anaphase checkpoint

Answer: (B)

Verified step by step guidance

1. Understand the concept of cell cycle checkpoints: These are control mechanisms in the cell cycle that ensure proper division and prevent errors. They act as 'quality control' points to verify whether the cell is ready to proceed to the next phase.
2. Review the G1/S checkpoint: This checkpoint occurs at the transition from the G1 phase (cell growth) to the S phase (DNA synthesis). It is crucial for assessing whether the cell has adequate size, nutrients, and undamaged DNA to proceed with replication.
3. Compare the G1/S checkpoint to the G2/M checkpoint: The G2/M checkpoint occurs later in the cycle, ensuring that DNA replication is complete and undamaged before entering mitosis. While important, it does not prevent premature division as effectively as the G1/S checkpoint.
4. Understand why the G1/S checkpoint is critical: This checkpoint prevents cells from entering the S phase prematurely, ensuring proper timing and conditions for DNA replication. It is the primary checkpoint for maintaining the integrity of the cell cycle.
5. Eliminate other options: The cytokinesis checkpoint occurs after mitosis and ensures proper division of the cytoplasm, while the metaphase/anaphase checkpoint ensures chromosomes are properly aligned before separation. Neither of these checkpoints directly prevents premature division like the G1/S checkpoint.