The Cell Cycle

Growth Phase 1
1. Cellular contents apart from chromosomes are duplicated.
Growth Phase 1 Checkpoint
1. At the end of G1 the cells are checked for specific markers.
  1. Checked for...
    1. Nutrients
      1. Growth Factors
        DNA damage
        Cell Size
  2. If all markers are satisfied the cell is triggered to enter the Synthesis phase. If not the cell enters G0
G0
1. Where the cell enters permanent cell arrest (no longer viable) if...
  1. Cell becomes specialised (no longer able to divide)
  2. Is no longer able to carry out it's functions indefinately
  3. If DNA is damaged (harmful mutation)
2. The majority of cells (normal) divide a limited number of times eventually becoming senescent
  1. Senescent - A cell that is no longer capable of dividing but still alive and metabolically active
Synthesis Phase
1. Each of the chromosomes in the cell is duplicated
Growth Phase 2
1. The cell checks the duplicated chromosomes for error
  1. Makes repairs if necessary
Growth Phase 2 Checkpoint
1. At the end of G2 phase the cell is again checked for specific markers.
  1. Cell checked for...
    1. Size of cell
      1. DNA replication
        DNA damage
Mitotic Phase
1. Mitosis
  1. Prophase
    1. First phase of mitosis Chromosomes become visible, nuclear envelop dissolves, spindle forms Chromatin condenses into chromosomes
  2. Metaphase
    1. Second phase of mitosis Chromosomes line up in the middle of the cell Metaphase Plate
  3. Anaphase
    1. Third phase of mitosis during which chromatids separate and are pulled to opposite sides of the cell
  4. Telophase
    1. the final stage of meiosis when the chromosomes move toward opposite ends of the nuclear spindle. The chromosomes start to uncoil and the nucleolus is formed and the nuclear envelope reforms.
2. Cytokinesis
  1. After Mitosis the cytoplasm divides and two cells are produced
  2. Starts in Telophase

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