Cell Cycle

Actively dividing cells undergo a series of stages known as the cell cycle.

  • Gap 0 (G0; quiescent phase)
    • Most non-proliferative cells in the body are in this phase and are not actively replicating.
  • Interphase
    • Gap 1 (G1)
      • Metabolic changes prepare the cell for division.  At a certain point (restriction point or G1 checkpoint), the cell is committed to division and moves onto S-phase
    • Synthesis phase (S phase)
      • DNA synthesis replicates the genetic material such that each chromosome is duplicated into two chromatids
    • Gap 2 (G2)
      • Metabolic changes assemble the cytoplasmic materials required for mitosis and cytokinesis
  • Mitotic phase (M phase)
    • Prophase
      • Nuclear membrane breaks down into a number of small vesicles
      • Centrosome duplicates and each one migrates to opposite poles of the cells where they organise production of microtubules that form spindle fibres (mitotic spindle)
      • Chromosomes condense into compact structures.  Sister chromatids are held together via the centromere structure
    • Prometaphase
      • Chromosomes migrate to the middle of the cell (the metaphase plate).
      • Spindle fibres attach to centromeres of the chromosomes.
    • Metaphase
      • Chromosomes align along the metaphase plate
    • Anaphase
      • Centromeres divide and daughter chromatids are pulled apart by spindle fibres
    • Telophase
      • Nuclear membrane reforms around the new chromosomes at either pole of the cell.
      • Chromosomes uncoil and become diffuse once more and spindle fibres are broken down
    • Cytokinesis
      • Constriction of the cytoplasm to divide into two new cells.

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