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.