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					    Mitotic Cell Division




1
    Objectives


         Learn preparing and staining procedure to identify
          the stages of mitosis in onion root tip.
         To differentiate between the different stages of
          mitosis.
         Calculate the mitotic index.




2
           Types of Cell Division

    –   Mitosis
          Producestwo new daughter cells with the same
          number and kind of chromosomes as the parent cell
    –   Meiosis
          Reduction  division produces progeny cells with one-
           half the genetic content and number of chromosomes
           as parent cell
          Produces gametes/spores


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                            Mitosis
       Purpose:
        –   Mitosis occurs in order for organisms to grow and
            develop.
        –   In order to replenish dead or dying cells such as
            skin cells, and cells in the digestive tract.
       Karyokinesis
        –   process of nuclear division (division of genetic
            material)
       Cytokinesis
        –   Process of dividing cytoplasm/cell
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    The Cell Cycle

       The life of a cell is divided into three stages known as
        the cell cycle:
    1. Interphase:
        cell carries out normal functions and prepares to
        divide
    2. Mitosis:
        nucleus divides splits into two
    3. Cytokinesis:
        cell and contents divide into two daughter cells.

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    Cell Cycle




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    G0




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    Interphase

       This phase consist of the G1,S,
        and G2 phases of the cell cycle.
       The chromatin is diffuse.
       It may not look like much is going
        on here, but there is a lot of
        activity because the cell must
        prepare for Mitosis:
       protein synthesis,
       DNA synthesis,
       replication of other cellular
        structures.
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    Mitosis

        There are 4 main phases:
             Prophase,
             Metaphase,
             Anaphase,
             Telophase.

        Cytokinesis (division of the
         cytoplasm) follows and one cell
         becomes two.
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     Mitosis: Prophase

     Major processes during this phase:
      Chromosomes condense and form
       visible bodies
      Chromosomes become thicker,
       shorter, and easily visible when
       stained under the light microscope.
      Two “sister chromatids” join near
       their middle at a structure called the
       centromere.
      The nucleolus and the nuclear
       membrane disappear. The mitotic
       apparatus the spindle, begins to
       organize within the cell
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     Mitosis: Metaphase

        Chromosomes         become
         aligned at midpoint or
         equator between poles of
         the cell
        are at their thickest and
         shortest structure.
        They are easily identified as
         two longitudinally double
         sister chromatids.


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     Mitosis: Anaphase

        The centromere
         replicates and splits
        The sister chromatids
         separate and are pulled
         to opposite sides of the
         cell



12
         Mitosis: Telophase

      Chromosomes now uncoil
      Nuclear envelope reappears and
       surrounds the chromosomes
     Cytokinesis
      The cytoplasm and all its contents are
       divided between the 2 daughter cells
       (cytoplasmic division)
      membrane creates between the 2 new
       daughter cells
      In plants, such as the onion root tip
       cells, this is seen as the formation of a
       cell plate
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     Stages of mitosis in onion root tip cells




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     Mitosis in Root Tip

        In a growing plant root, the cells at the tip of
         the root are constantly dividing to allow the
         root to grow.
        Because each cell divides independently of
         the others, a root tip contains cells at
         different stages of the cell cycle.
        This makes a root tip an excellent tissue to
         study the stages of cell division
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     Experiment


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     Materials

        Slides & cover slips
        Microscope
        Fresh onion root tips
        Fixative ( methanol-acetic acid 3:1 v/v)
        Forceps
        1 M HCl
        Razor blade
        Stain
        Paper towel, or absorbent paper

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     Method
        Cut 2-3 mm of onion root
        Use forceps to transfer an onion root tip into the cup of
         HCl.
        Leave for 4 minutes
        Transfer the root tip to the cup containing fixative and
         leave it for 4 minutes.
        Then place the root tip on a slide.
        Cover the root tip with a few drops of stain for 2
         minutes
        Cover the root tip with one to two drops of 45% acetic
         acid
        Put a cover slip over the root, put a paper towel or
         other absorbent paper and with your thumb firmly press
21       on the cover slip.
        Observe your preparation under the low power (X10) of a
         microscope
        Search the slide to find cells in various stages of cell division,
         once you have located cells in division, change to high power
         (X40) & try to observe several stages of division.
        Record the number of cells in each stage. Count at least
         three full fields of view. You should have counted over 200
         cells.
        Record your data in the table
        Calculate the percentage of cells in each phase and record in
         the table


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     Mitotic index

        A measure for the proliferation status of a cell
         population.
        It is defined as the ratio between the number
         of cells in mitosis and the total number of
         cells.




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     Animation

     http://www.youtube.com/watch?v=s1ylUTbX
       yWU




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     Interphase               Prophase




     Metaphase                Anaphase




                  Telophase




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posted:10/21/2011
language:English
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