03 cell division


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03 cell division

  2. 2. CELL DIVISION Why do cells need to divide? -To allow an organism to grow -To pass on genetic material -To assist an organism’ survival
  3. 3. CELL DIVISION 2 types of cell division Mitosis Meiosis -daughter cells are genetically identical -daughter cells are genetically different
  4. 4. CELL DIVISION Mitosis 5 stages: - Literally refers to the division of the nucleus Interphase Prophase Metaphase Anaphase Telophase
  5. 5. CELL DIVISION Interphase - Cell is not dividing but also not dormant - Cell is active and growing and also preparing for division - Sometimes called resting phase but this is inaccurate (real resting phase is G0) - DNA/chromosomes not visible (unwound)
  6. 6. CELL DIVISION Interphase: 4 stages Gap 0 (G0): - Cell rest cycle - may be temporary or permanent (where cells are functional but no new cells are produced (i.e. neuron) G0
  7. 7. CELL DIVISION Interphase: 4 stages Gap 1 (G1): - Rapid growth (4hr) - cell takes in nutrients for energy, growth, repair - Cells either go into S or G0 after G1 G0
  8. 8. CELL DIVISION Interphase: 4 stages S phase (S): - 10 hrs - DNA synthesis/ replication - the cell duplicates its genetic material to make an identical copy of its DNA G0
  9. 9. CELL DIVISION Interphase: 4 stages Gap 2 phase (G2): - 3-4hr - second period of growth in preparation for cell division -cell grows larger in size G0
  10. 10. CELL DIVISION S phase (S): Let’s take a closer look DNA replication DNA duplication Normally After duplication
  11. 11. CELL DIVISION How does all of the DNA remain organized in the nucleus? Why does it not tangle?
  12. 12. CELL DIVISION DNA strands are wrapped around histone proteins which act as “spools”
  13. 13. CELL DIVISION Histone proteins that have been wrapped with DNA form “nucleosomes”
  14. 14. CELL DIVISION Moving into mitosis… After interphase, the cell may enter mitotic (M) phase: - A process by which somatic cells grow and divide - Cells come from pre-existing cells - Parent cell divides to produce two new identical daughter cells - Cell division occurs through: - A) Mitosis – process of dividing nuclear material - B) Cytokinesis – Process of separating the cytoplasm and its contents into equal parts
  15. 15. CELL DIVISION Prophase - nuclear membrane breaks down - chromosomes shorten and thicken - Other structures important for mitosis are also forming (i.e. the centrioles)
  16. 16. CELL DIVISION Prophase - chromosomes shorten and thicken into X-shaped things
  17. 17. CELL DIVISION Prophase - A centromere holds two copies of the same chromosome together - Each copy of a chromosome is called a chromatid
  18. 18. CELL DIVISION Prophase - A centromere holds two copies of the same chromosome together - Remember, every chromosome has been duplicated during the S phase of interphase. Colors are not accurate - Recall this: Mitosis Mother’s side Mother’s side Mother’s side
  19. 19. CELL DIVISION Prophase
  20. 20. CELL DIVISION Metaphase - Proteins attach to the centromeres creating the kinetochores. - Microtubules (spindle fibres) attach at the kinetochores and the chromosomes move to the centre (the metaphase plate)
  21. 21. CELL DIVISION Metaphase
  22. 22. CELL DIVISION Anaphase - Paired chromosomes separate at the kinetochores and move to opposite sides of the cell - Motion results from kinetochore movement along the spindle microtubules
  23. 23. CELL DIVISION Telophase - Chromatids arrive at opposite poles of cell - New membranes form around the daughter nuclei - Chromosomes disperse and are no longer visible under the light microscope - spindle fibres disperse
  24. 24. CELL DIVISION Cytokinesis - Animal cells: the cell membrane pinches (forming a cleavage furrow) into two daughter cells, each with one nucleus
  25. 25. CELL DIVISION Cytokinesis - In plant cells, a cell plate (made of rigid cellulose) is synthesized between the two daughter cells.
  26. 26. CELL DIVISION Mitosis and cytokinesis: Review