08 The cell cycle


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08 The cell cycle

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