01 Cell Reproduction

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01 Cell Reproduction

  1. 1. CELL REPLICATION<br />(in prokaryotes & eukaryotes)<br />
  2. 2. Binary fission in bacteria<br />Much faster than mitosis in eukaryotic cells<br />Takes approx. 20 mins as opposed to several hours<br />If resources were available once cell could become 16,000,000 in 8 hours!<br />
  3. 3. Binary Fission in bacteria<br />
  4. 4. Binary Fission in bacteria<br />Bidirectional replication of circular DNA<br />
  5. 5. Binary Fission in bacteria<br />DNA moves to poles<br />
  6. 6. Binary Fission in bacteria<br />Cell elongates<br />Cleavage furrow forms<br />
  7. 7. Binary Fission in bacteria<br />Cell divides<br />
  8. 8. The Cell Cycle – Eukaryotic cells<br />Final checkpoint <br />at the end of metaphase<br />
  9. 9. Animations<br />Animation 1<br />Animation 2<br />
  10. 10. The Cell Cycle – G1<br />The first phase is a growth phase (G1)<br />The new cell starts growing and replicating its organelles<br />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.<br />If the cell is under any sort of stress, it will pause at this stage.<br />
  11. 11. The Cell Cycle - S<br /><ul><li>During the synthesis (S) phase, DNA replication occurs
  12. 12. 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
  13. 13. DNA replication is semi-conservative – every new molecule consists of one original strand and one new strand.
  14. 14. DNA replication involves numerous enzymes
  15. 15. Helicase and gyrase unwind and unzip to strands of DNA
  16. 16. DNA polymerase continuously adds nucleotides to the leading strand in a 5’ to 3’ direction
  17. 17. RNA primase makes an RNA primer on the lagging strand
  18. 18. DNA ligse sticks together prefabricated ‘Okazaki’ fragments made by DNA polymerase to replace the RNA</li></li></ul><li>The Cell Cycle – G2<br />During the next growth phase (G2), the cell continues to grow in preparation for division<br />The checkpoint during this phase is extremely important.<br />If any errors have occurred during transcription, the cell must undergo apoptosis (programmed cell death)<br />
  19. 19. The Cell Cycle - M<br />During Mitosis (M), the single parent cell gives rise to two identical daughter cells.<br />Another checkpoint occurs at the end of metaphase to ensure that chromosomes are aligned and that spindle fibres are attached corectly.<br />A negative result at the checkpoint here will result in apoptosis.<br />
  20. 20. The Cell Cycle - C<br />Cytokynesis (C) is actually the last part of Mitosis<br />At this point the cell, which momentarily has twin nuclei, will divide in to two new cells (2n) and the process will begin again.<br />
  21. 21. What happens if the checkpoints don’t work?<br />If cell cycle checkpoints are operated by enzyme proteins.<br />These enzymes can be prevented from carrying out normal function by inhibitors.<br /> These enzymes could also be stimulated to maintain an active state permanently.<br />Either way can lead to uncontrolled and unmonitored cell division, this is commonly known as ….<br />
  22. 22. CANCER<br />Cells multiply uncontrollably and regardless of accumulating errors will never apoptose.<br />Does not form useful cells as cells spend far more time in division rather than growth (a reversal of the normal situation).<br />
  23. 23. MITOSIS <br />
  24. 24. InterphaseThe cell prepares for division<br />2N - 4N<br />Animal & Plant Cells <br />Nucleus clearly defined<br />Chromosomes not yet visible<br />DNA replicated<br />Organelles replicated<br />Cell increases in size<br />
  25. 25. Interphase<br />Plant Cell<br />Animal Cell<br />Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm<br />
  26. 26. ProphaseThe cell prepares for nuclear division<br />4N<br />Animal & Plant Cells<br />DNA packaged in to chromosomes<br />Nuclear envelope disappears<br />Centrioles move to opposite sides of the cell<br />
  27. 27. Prophase<br />Plant Cell<br />Animal Cell<br />Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm<br />
  28. 28. MetaphaseThe cell prepares chromosomes for division<br />4N<br />Animal & Plant Cells<br />Chromosomes line up at the center of the cell<br />Spindle fibres attach to centromeres on the chromosomes<br />Centrioles reach the opposite poles of the cell<br />
  29. 29. Metaphase<br />Plant Cell<br />Animal Cell<br />Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm<br />
  30. 30. AnaphaseThe chromosomes divide<br />4N<br />Animal & Plant Cells<br />Spindle fibers contract and pull chromosomes apart<br />½ of each chromosome (called a chromatid) moves to each hemisphere<br />Unattached spindle fibres push against each other or the sides of the cell, and it begins to elongate<br />
  31. 31. Anaphase<br />Plant Cell<br />Animal Cell<br />Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm<br />
  32. 32. TelophaseThe cytoplasm divides<br />4N - 2N<br />Plant Cell<br />DNA spreads out<br />2 nuclei form<br />Cell plate forms new cell wall between the nuclei to form the 2 new daughter cells<br />Animal Cell<br />DNA spreads out<br />2 nuclei form<br />Contractile ring causes a cleavage furrow to form the 2 new daughter cells<br />
  33. 33. Telophase<br />Plant Cell<br />Animal Cell<br />Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm<br />
  34. 34. MitosisAnimations<br />Mitosis.exe<br />Mitosis Animation<br />
  35. 35. Animal Mitosis -- Review<br />
  36. 36. Plant Mitosis -- Review<br />
  37. 37. Summary of Mitosis<br />Prophase: <br />Chromosomes condense<br />Nuclear envelope disappears<br />centrosomes move to opposite sides of the cell<br />Spindle forms and attaches to centromeres on the chromosomes<br />Metaphase<br />Chromosomes lined up on equator of spindle<br />centrosomes at opposite ends of cell<br />Anaphase<br />Centromeres divide: each 2-chromatid chromosome becomes two 1-chromatid chromosomes<br />Chromosomes pulled to opposite poles by the spindle<br />Telophase<br />Chromosomes de-condense<br />Nuclear envelope reappears<br />Cytokinesis: the cytoplasm is divided into 2 cells<br />
  38. 38. MEIOSIS <br />
  39. 39. Recombination through meiosis<br />DNA replicates<br />Crossing over<br />Random <br />assortment<br />First division<br />Second <br />random <br />assortment<br />Second <br />division<br />
  40. 40. Mitosis vs. meiosis<br />
  41. 41. Getting the names right<br />Centromere<br />Spindle fibres / <br />microtubules<br />Kinetochore<br />Sister chromatids<br />
  42. 42. Recombination = variation<br /><ul><li>2 pairs of chromosomes = 4 possibilities
  43. 43. 4 pairs of chromosomes = 8 possibilities
  44. 44. What are the chances of identical offspring?
  45. 45. 2n = 46 (not incl. twins) 1 / 16,777,216</li></li></ul><li>DNA Replication<br />DNA is uncoiled and unzipped by helicase & gyrase<br />The original strands are called the template strands<br />The new strands are called the complementary strands<br />The 3’ to 5’ template strand is the leading strand<br />The 5’ to 3’ template strand is the lagging strand<br />The complementary strand can only be written 5’ to 3’<br />DNAi ANIMATIONS x 2<br />
  46. 46. The leading strand<br />An RNA primer is put down by RNA polymerase<br />Complementary DNA is put down base-pair by base-pair by DNA polymerase<br />DIRECTION OF REPLICATION<br />3’ 5’<br />Rp<br />Dp<br />5’<br />3’<br />
  47. 47. The lagging strand<br />RNA polymerase puts down primers along the template strand of DNA<br />DNA polymerase III builds short ‘Okazaki’ fragments from each primer<br />DNA polymerase I removes the RNA and replaces it with DNA<br />DNA ligase sticks the fragments together<br />
  48. 48. The lagging strand<br />RNA Polymerase<br />DNA Polymerase III<br />DNA Polymerase I<br />DNA Ligase<br />DIRECTION OF REPLICATION<br />5’ 3’<br />3’<br />5’<br />
  49. 49. Additional info on cell reproduction<br />Our cells can be categorised in to two types<br />Somatic cells (diploid)<br />Germline cells (diploid but give rise to haploid gametes – sperm & eggs)<br />
  50. 50. Biozone Fun!<br />DNA replication<br />pp. 203-25<br />Cell cycle, mitosis, apoptosis<br />pp. 209-212<br />Meiosis<br />pp. 287-290<br />

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