1 / 69

Cell Division

Cell Division. Why divide?. Characteristic of life Continuity Growth (zygote → multicellular org) Repair, renewal, replacement. Requirements. Distribution of identical DNA to daughter cells. Figure 12.0 Mitosis. DNA – a closer look. Genome – cell’s entire genetic info

bonner
Download Presentation

Cell Division

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cell Division

  2. Why divide? • Characteristic of life • Continuity • Growth (zygote → multicellular org) • Repair, renewal, replacement

  3. Requirements • Distribution of identical DNA to daughter cells

  4. Figure 12.0 Mitosis

  5. DNA – a closer look • Genome – cell’s entire genetic info • Prok – often a single long DNA molecule • Euk – several DNA molecules • Human cells must copy ~ 3 m of DNA before division

  6. Packaging DNA • Chromosomes • Contain DNA and Protein • Called chromosomes because they can be stained with certain dyes

  7. Eukaryotic Chromosomes • Composed of CHROMATIN • protein • DNA • Chromosomes become visible as distinct structures when the cell divides • When not dividing, the chromosomes decondense

  8. Chromosome Structure • Duplicated chromosome = 2 sister chromatids • Chromatids → identical copies of the DNA • As they condense, the area where strands connect shrinks → centromere

  9. Genes • Organization of DNA informational units • Chromosomes contain hundreds to thousands of genes • Humans: 35,000 - 45,000 genes

  10. Number of Chromosomes • Differ by species • Humans - 46 chrom (somatic cells) • The number is not indicative of complexity What is this called? KARYOTYPE

  11. Gametes • Gametes contain half the # of chromosomes present in somatic cells • Human gametes – 23 chromosomes • WHY?

  12. Cell Cycle • A sequence of cell growth and division • Numerous factors control when cells divide • Cell Division • Mitosis- division of chromosomes • Cytokinesis- division of cytoplasm

  13. Cell Cycle • Chrom duplicate during INTERPHASE (90% of cell’s life) • G1 phase - cells grow and synthesize biological molecules • S phase - DNA replication • G2 phase - gap of time between S phase and mitosis (preparation for division)

  14. Mitosis • Purpose is to ensure the orderly distribution of chromosomes • Four Stages: • Prophase • Metaphase • Anaphase • Telophase

  15. Late Interphase • Chrom duplicated, still loosely packed • Centrosomes duplicated, organization of microtubules into an “aster”

  16. Mitosis – Prophase (early) • Duplicated chromosomes visible • Chromatin condenses • Sister chromatids are bound at the centromere • Centromeres have kinetochores (proteins) to which microtubules will bind

  17. Mitosis – Prophase (early) • The mitotic spindle, composed of microtubules, forms between the poles • The MTOC (microtubule organizing center) surrounds a pair of centrioles in animal cells and some plant cells • Centrioles are surrounded by pericentriolar material

  18. Mitosis – Prophase (middle) • Asters extend from the MTOCs at the poles (in cells that have centrioles) • The nucleolus disappears

  19. ASTER

  20. Mitosis – Prophase (late) • The nuclear envelope disappears

  21. Mitosis - Metaphase • Duplicated chromosomes line up at midplane • Chromatids are highly condensed • Polar microtubules extend from the pole to the equator, typically overlap • Kinetochore microtubules extend from the pole to the kinetochores

  22. Mitosis – Anaphase (early) • Chromosomes move toward the poles • Chromatids separate at the centromeres and are now referred to as chromosomes

  23. Mitosis – Anaphase (late) • The chromosomes are pulled by the kinetochore microtubules to the poles and form a “V” shape • The movement mechanism by which the microtubules and other mitotic spindle components move the chromosomes is largely unknown

  24. Mitosis- Telophase • Two separate nuclei form • Cell returns to conditions similar to interphase • Nuclear envelope reforms; nucleoli reappear • Cytokinesis occurs

  25. Cytokinesis • Formation of two separate daughter cells • Begins during telophase • In animals cells, a furrow develops caused by contractile actin filaments that encircle the equatorial region • In plant cells, a cell plate forms originating from the Golgi complex

More Related