Which of the following is not a checkpoint that controls the progression of the cell cycle?

• A. M checkpoint
• B. G1/S checkpoint
• C. S/G2 checkpoint
• D. G2/M checkpoint

Answer: (C)

Verified step by step guidance

1. Understand the concept of cell cycle checkpoints: These are control mechanisms in eukaryotic cells which ensure proper division of the cell. They verify whether the processes at each phase of the cell cycle have been accurately completed before the cell progresses to the next phase.
2. Identify the main checkpoints in the cell cycle: The primary checkpoints are the G1/S checkpoint, G2/M checkpoint, and the M checkpoint. Each of these has specific roles in monitoring and regulating the cell cycle.
3. G1/S checkpoint: This checkpoint ensures that the cell is ready for DNA synthesis. It checks for cell size, nutrients, growth factors, and DNA damage.
4. G2/M checkpoint: This checkpoint ensures that the cell is ready to enter mitosis. It checks for DNA replication completeness and DNA damage.
5. M checkpoint: Also known as the spindle checkpoint, it ensures that all chromosomes are properly attached to the spindle apparatus before anaphase begins. The S/G2 checkpoint is not a recognized checkpoint in the cell cycle, hence it is the correct answer.