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The Great Divide

Mitosis:. The Great Divide. 05/04. 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)

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The Great Divide

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  1. Mitosis: The Great Divide 05/04

  2. 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) So what’s a cell to do? DIVIDE !!!!

  3. Why Would a Cell Divide? Besides growth a cell would also divide for: Repair or Replacement Cancer Different cells divide at different rates: Most mammalian cells = 12-24 hours Some bacterial cells = 20-30 minutes

  4. 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

  5. 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 = apoptosis (programmed cell death)

  6. The Cell Cycle

  7. Stages of the Cell Cycle interphase (growth & replication of DNA) mitotic phase (division of cell into 2 daughter cells) There are two stages to a cells life. Cell spends about 90% of the time in interphase

  8. Interphase • Divided into 3 phases: • G1 (1st gap) = small cell is absorbing nutrients, growing & doing its job. • S (synthesis) = cell is continuing to grow & duplicates its DNA. • G2 (2nd gap) = cell keeps growing & doing its job.

  9. Mitosis: A Closer Look DNA is all twisted up into a Chromosome. • During S phase the Chromosome is copied. • 2 complete identical sets of chromosomes. • They are connected in the middle by a centromere. • A single copied chromosome is called a Chromatid.

  10. The Mitotic Phase • Divided into 4 stages of Mitosis: • Prophase • Metaphase • Anaphase • Telophase (+) PLUS • Cytokinesis

  11. Prophase Chromatids condense becoming visible. Nuclear membrane dissolves The centrioles (an organelle that makes microtubules) appears and migrate to opposite sides. spindle fibers start to form between them • http://www.biostudio.com/demo_freeman_dna_coiling.htm

  12. Metaphase Chromosomes line-up on the metaphase plate Centromeres are attached to spindle fibers

  13. Anaphase Spindle fibers contract Centromeres divide Sister chromatids are pulled away from each other towards the poles

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

  15. Cytokinesis The cytoplasm distributed equally between the 2 new cells In animals, a cleavage furrow forms from outside in In plants, a cell plate forms from inside out Animal Plant

  16. What Mitosis Actually Looks Like Interphase Metaphase Prophase Telophase Anaphase http://www.sci.sdsu.edu/multimedia/mitosis/mitosis_gif2.html http://science.nhmccd.edu/biol/bio1int.htm

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

  18. 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

  19. The Guarentee • 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?

  20. The Daughter Cells • In humans, the 2 daughter cells will have 46 chromosomes (23 pairs) • Each chromosome is said to have the same gene sequence Identical daughter cells

  21. The Beauty of Asexual Reproduction • Mitosis is a form of asexual reproduction • New individuals are produced by 1 parent & thus, are identical to their parent Mother cell Runners produces by strawberries Identical daughter cells Budding by hydra & yeast Cuttings from plants

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