Interphase

• G1 (Cell Growth Checkpoint)

  • Cellular contents, excluding the chromosomes, are duplicated.
  • Occurs toward the end of growth phase 1 (G1).
  • Checks whether the cell is big enough and has made the proper proteins for the synthesis phase.
  • If not, the cell goes through a resting period (GO) until it is ready to divide.
• S (DNA Synthesis Checkpoint)

  • Each of the 46 chromosomes is duplicated by the cell.
  • Occurs during the synthesis phase (S).
  • Checks whether DNA has been replicated correctly
  • If so, the cell continues on to mitosis (M).
• G2

  • The cell "double checks" the duplicated chromosomes for error, making any needed repairs.
• Mitosis Checkpoint

  • Occurs during the mitosis phase (M).
  • Checks whether mitosis is complete.
  • If so, the cell divides, and the cycle repeats.