Mitosis - PowerPoint PPT Presentation

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Mitosis

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just before cell division, chromatin compacts and reorganizes into chromosomes ... Formed by a contractile ring of actin filaments. Like pulling on a draw string ... – PowerPoint PPT presentation

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Title: Mitosis


1
Mitosis
  • Chapter 9

2
Cell Division
  • process by which new identical cells are produced
    from existing cells
  • stomach and intestine cells every 2-3 days
  • skin cells every 20 days
  • liver cells every 200 days
  • brain cells reproduce every 30-50 years

3
Chromosomes
  • short, stringy structures of DNA
  • carriers of genetic material
  • usually chromatin long strands of DNA which are
    wrapped around histone proteins
  • just before cell division, chromatin compacts and
    reorganizes into chromosomes
  • each chromosome internally duplicated
  • consists of two identical DNA chains (sister
    chromatids) attached together at a single point
    (centromere)

4
Chromosome Structure
5
Mitosis in Animal Cells
  • outside nucleus centrosome (microtubule
    organizing center)
  • organizes mitotic spindle
  • contains many fibers each composed of a bundle of
    microtubules
  • in animals, contains two centrioles
  • oriented at right angles to each other
  • each with 9 triplets of microtubules arranged in
    a cylinder
  • Centrosome was also replicated in S-phase, so now
    two centrosomes

6
Mitosis Phase One Prophase
  • longest phase of mitosis
  • chromatin has condensed (visible in microscope)
  • nuclear envelope and nucleolus disintegrate
  • centrioles move to ends of cell (in animals)
  • form microtubules in star-like arrays called
    asters
  • spindle forms
  • football-shaped, cagelike structure make up of
    microtubules
  • in plants, spindle does not need centrioles

7
Pictures of Prophase
8
Prometaphase
  • centromeres develop two kinetochores
  • specialized protein complex
  • 1 over each sister chromatid
  • physically hook sister chromatids up with
    specialized microtubules (kinetochore fibers)
  • connect sisters to opposite poles of mother cell

9
Mitosis Phase Two Metaphase
  • spindle fibers attach to chromosomes at
    kinetochores
  • chromosomes are lined up across equatorial plane
  • metaphase plate (looks like glass) shows where
    mother cell will be divided

10
Mitosis Phase Three Anaphase
  • centromeres dissolve
  • daughter chromosomes separate and are pulled to
    opposite ends of cell by the shortening of the
    kinetochore fibers

11
Mitosis Phase Four Telophase
  • begins as daughter chromosomes reach opposite
    ends
  • chromosomes unwind to become chromatin
  • spindle breaks down
  • nucleolus reappears nuclear envelope forms

12
Cytokinesis
  • cytoplasm divides to form two separate, identical
    cells
  • animal cytokinesis
  • A cleavage furrow appears between daughter nuclei
  • Formed by a contractile ring of actin filaments
  • Like pulling on a draw string
  • Eventually pinches mother cell in two

13
Cytokinesis in Animals
14
Cytokinesis in Plants
  • cell walls do not permit furrowing
  • begins with formation of a cell plate
  • many small membrane-bounded vesicles
  • eventually fuse into one thin vesicle extending
    across the mother cell
  • membranes of the cell plate become the plasma
    membrane between the daughter cells
  • contents of vesicles become the middle lamella
    between the two daughter cells
  • daughter cells later secrete primary cell walls
    on opposite sides of middle lamella

15
Cytokinesis in Plants
16
Animation of Stages of Mitosis
Mitosis takes 30 minutes to 1 ½ hours depending
on the type of cell Remember I P MAT C
17
Results of Mitosis
  • guarantees genetic continuity with two identical
    cells
  • unicellular organisms simply multiply into two
    organisms they do not become multicellular
    organisms
  • multicellular organisms form tissues, organs, and
    organ systems as a result of mitosis
  • Identify which of the following examples in the
    video clip are actually mitosis

18
The End
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