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08 The cell cycle
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08 The cell cycle


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  • 1. The Cell Cycle Final checkpoint during mitosis
  • 2. Animations Animation 1 Animation 2
  • 3. The Cell Cycle – G1
    • The first phase is a growth phase (G1)
    • The new cell starts growing and replicating its organelles
    • At the end of G1, the checkpoint is to gauge if it is a good time for cell to keep growing or dividing or if a delay is necessary.
    • If the cell is under any sort of stress, it will pause at this stage.
  • 4. The Cell Cycle - S
    • During the synthesis (S) phase, DNA replication occurs
    • It is at this point that the diploid cell (2n) doubles to 4n, so that when it divides there will be two complete copies of the DNA
  • 5. The Cell Cycle – G2
    • During the next growth phase (G2), the cell continues to grow in preparation for division
    • The checkpoint during this phase is extremely important.
    • If any errors have occurred during transcription, the cell must undergo apoptosis (programmed cell death)
  • 6. The Cell Cycle - M
    • During Mitosis (M), the single parent cell gives rise to two identical daughter cells.
    • Once again a checkpoint assesses whether any errors have occurred during division.
    • A negative result at the checkpoint here will result in apoptosis.
  • 7. The Cell Cycle - C
    • Cytokynesis (C) is actually the last part of Mitosis
    • At this point the cell, which momentarily has twin nuclei, will divide in to two new cells (2N) and the process will begin again.
  • 8. What happens if the checkpoints don’t work?
    • If cell cycle checkpoints are operated by enzyme proteins.
    • These enzymes can be prevented from carrying out normal function by inhibitors.
    • These enzymes could also be stimulated to maintain an active state permanently.
    • Either way can lead to uncontrolled and unmonitored cell division, this is commonly known as ….
  • 9. CANCER
    • Cells multiply uncontrollably and regardless of accumulating errors will never apoptose.
    • Does not form useful cells as cells spend far more time in division rather than growth (a reversal of the normal situation).
    • How does chemotherapy help?
  • 10. Chemotherapy
    • During interphase, DNA is somewhat protected from radiation due to the double membrane of the nucleus.
    • During mitosis there is no nuclear envelope to protect the DNA
    • Chemotherapy destroys DNA, thus kills far more cancer cells than budy cells as they spend far more time dividing
    • The collateral damage of killing healthy body cells is what makes people sick when undergoing chemotherapy (and makes their hair fall out)