What are the four main stages of the cell cycle, and what key events and checkpoints occur in each?

What are the four main stages of the cell cycle, and what key events and checkpoints occur in each?

• A. G1 (growth and the restriction point); S (DNA replication); G2 (growth and preparation for mitosis); M (mitosis and cytokinesis); Checkpoints: G1/S, G2/M, and spindle assembly checkpoint during M.
• B. G1 is DNA replication; S is growth; G2 is fermentation; M is meiosis; No checkpoints.
• C. The cell cycle consists only of G1 and S phases with no other events.
• D. G1 is for growth and the restriction point; S is DNA replication; G2 is growth and preparation for mitosis; M is mitosis and cytokinesis; Checkpoints: G1/S, G2/M, and the spindle assembly checkpoint during M.

Answer: (B)

The four stages of the cell cycle are arranged to coordinate growth, DNA duplication, and cell division. G1 is a growth and metabolic phase where the cell increases in size and carries out normal functions; a point at the end of G1 acts as a gate (the G1/S checkpoint) to decide whether conditions are right to duplicate DNA. The S phase is when the genome is precisely replicated, so each chromosome is copied once. G2 is another growth and preparation phase, ensuring that DNA has been replicated correctly and the cell is ready for mitosis; the G2/M checkpoint checks for any DNA damage or replication errors before division begins. M is mitosis and cytokinesis, where the nucleus divides and the cell splits into two; during this stage the spindle assembly checkpoint ensures all chromosomes are properly attached to the spindle before sister chromatids separate, preventing mis-segregation. In short, the cycle progresses through growth, DNA replication, final prep, and division, with checkpoints at the G1/S boundary, the G2/M boundary, and during mitosis to ensure accurate and complete division.

The four stages of the cell cycle are arranged to coordinate growth, DNA duplication, and cell division. G1 is a growth and metabolic phase where the cell increases in size and carries out normal functions; a point at the end of G1 acts as a gate (the G1/S checkpoint) to decide whether conditions are right to duplicate DNA. The S phase is when the genome is precisely replicated, so each chromosome is copied once. G2 is another growth and preparation phase, ensuring that DNA has been replicated correctly and the cell is ready for mitosis; the G2/M checkpoint checks for any DNA damage or replication errors before division begins. M is mitosis and cytokinesis, where the nucleus divides and the cell splits into two; during this stage the spindle assembly checkpoint ensures all chromosomes are properly attached to the spindle before sister chromatids separate, preventing mis-segregation.

In short, the cycle progresses through growth, DNA replication, final prep, and division, with checkpoints at the G1/S boundary, the G2/M boundary, and during mitosis to ensure accurate and complete division.