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The Great Divide

Mitosis:. The Great Divide. “MITOSIS IN A NUTSHELL”. To Be Answered…. THINK: How many cells are you composed of? When an organism grows bigger do you get more cells or just bigger cells or both? When do your cells divide the fastest? Slowest? Do cells ever stop dividing?

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The Great Divide

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  1. Mitosis: The Great Divide

  2. “MITOSIS IN A NUTSHELL”

  3. To Be Answered… • THINK: • How many cells are you composed of? • When an organism grows bigger do you get more cells or just bigger cells or both? • When do your cells divide the fastest? Slowest? • Do cells ever stop dividing? • Are all cells capable of division and replacement?

  4. WHY DO CELLS DIVIDE? • To keep a workable ratio of surface area to volume V = l x w x h SA = l x w x 6 1 cm 2cm 3 cm V = 1 cm3 V = 8 cm3 V = 27 cm3 SA = 6 cm2 SA = 24 cm2 SA = 54 cm2 Ratio = 6/1 Ratio = 24/8 Ratio = 96/64 6:1 3:1 2:1 -As cell gets larger, ratio decreases

  5. Why Would a Cell Divide? • As cells absorb nutrients and get larger, the volume of the cell increases faster than the surface area • This means that a cell can no longer absorb nutrients and get rid of wastes fast enough to support its demands (volume) = STARVE TO DEATH • So what’s a cell to do? • Solution: divide in 2! Surface area for exchange not great enough to support cell’s needs

  6. When Would a Cell Divide? • Growth • Repair or Replacement • Cancer Different cells divide at different rates: • Most mammalian cells = 12-24 hours • Some bacterial cells = 20-30 minutes

  7. Getting Older… • All cells are only allowed to complete a certain number of divisions • Then they die (programmed cell death) How does cell division change over a lifetime? • Childhood = cell division > cell death • Adulthood = cell division = cell death • The Later Years = cell division < cell death

  8. The Cell Cycle INTERPHASE

  9. Stages of the Cell Cycle • 2 stages = interphase (growth & replication of DNA) & mitotic phase (division of cell into 2 daughter cells) • Cell spends about 90% of the time in interphase

  10. Interphase • Divided into 3 phases: • G1 = Growth Phase – Cells grow and develop, undergo protein synthesis and rapid growth • S = Synthesis Phase - DNA replication occurs (i.e. chromosomes copied) in preparation for making new cells during mitosis • G2 =Second Growth Phase = centrioles replicate, cell prepares for cell division, makes new cell parts • Becomes too large = divide in 2

  11. The Mitotic Phase • Equal distribution of 2 sets of chromosomes (DNA) into 2 identical daughter cells • Divided into 4 stages of Mitosis: • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis

  12. Cell Cycle Tidbits How long is one cell cycle? • Depends on the cell- skin cells = ~24 hours, nerve cells = never after maturity, cancer cells = very short • Remember: every cell only has a certain # of divisions it can undergo, then it dies = (programmed cell death)

  13. Mitosis: A Closer Look • Prior to entering the mitotic phase, the cell has just come out of Interphase • Replicated DNA during S (synthesis) • 2 complete set of chromosomes that must be distributed equally between 2 cells = mitosis Interphase

  14. Prophase • Chromatin condenses visible chromosomes • Appear as sister chromatids held together by centromere • Nuclear membrane dissolves • The centrioles migrate to opposite poles & spindle fibers form between them

  15. Duplicated Chromosome

  16. Mitotic Appearance (Prophase) • Centriole • Centromere • Spindle • Chromosome (chromatids) • Aster

  17. Metaphase • Chromosomes line-up on the metaphase plate • Centromeres are attached to spindle fiber

  18. Anaphase • Centromeres divide • Spindle fibers contract • Result = sister chromatids are pulled away from one another towards the poles

  19. Telophase • The chromosomes reach the poles • Nuclear membranes form around the 2 new nuclei

  20. Cytokinesis • The cytoplam distrubted equally between the 2 new cells • In animals, the cell membrane pinches together • In plants, a cell plate forms from inside out Plant Animal

  21. Cytokinesis in plants A cell plate made up of cell-wall components gradually forms in the middle of the cell.

  22. Cytokinesis in animals Cleavage Furrow A cleavage(or division) of the animal cell. The membrane pinches together forming 2 cells

  23. ANIMAL VS. PLANT MITOSIS • ANIMAL CELL • Centriole and aster present • Daughter cells separated by cleavage furrow • PLANT CELL • No visible centriole or aster • Daughter cells separated by cell plate

  24. What Mitosis Actually Looks Like Interphase Metaphase Prophase Telophase Anaphase

  25. Figure 9.8 – Part 2 Figure 9.8 – Part 2 Mitosis consists of several different phases.

  26. Summary of Mitosis

  27. What Happens After Mitosis? • The cell returns to interphase • Chromosomes uncoil back into chromatin • The cycle repeats itself over & over…

  28. At What Stage Are Our Cells At In The Cell Cycle? • Different cells can be in different stages • Interphase • Mitosis: • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis

  29. Can You Identify the Stages of Mitosis? Put the following mitosis stages in the correct sequence

  30. Mitosis Can you name the stages? A B C D E

  31. The Guarantee • The product of mitosis is 2 cells • The daughter cells are identicalto each other & to the mother cell Mother cell Identical daughter cells Why is this so important?

  32. The Daughter Cells Mother cell • In humans, the 2 daughter cells will have 46 chromosomes (23 pairs) • 1 chromosome originally from mom & 1 from dad • Each chromosome is said to have the same gene sequence Identical daughter cells

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