MITOSIS

							The Cell Cycle
The process by which cells
         divide
         OBJECTIVES

 Understand   that cell division
  occurs in stages.
 Understand what happens in
  each of the stages.
 Understand the structure of DNA
  and the basic process of
  replication.
3 Stages of Cell Division
              The regular sequence
               of growth and division
               is called the cell
               cycle. This includes
               the following stages:
              Interphase
              Mitosis
              Cytokinesis
Stage 1: Interphase
This is the period before cell division
                occurs.
                      Growth. The cell
                       doubles in size and
                       makes copies of
                       organelles.
                      DNA replication.
                       The cell makes
                       copies of its DNA in
                       the nucleus.
                      Preparation for
                       division. The cell
                       produces structures
                       that it will use to
Stage 2: Mitosis
         The cell’s nucleus
          divides into two new
          nuclei.
         One copy of the DNA
          is distributed to each
          of the two daughter
          cells.
         Mitosis occurs in
          several specific steps.
Prophase
     DNA condenses and coils
      up.(The condensed,
      coiled DNA is now called
      a chromosome and
      contains identical copies
      of DNA strands held
      together by the
      centromere.)
     Nuclear membrane
      begins to break down.
     The spindle fibers form a
      bridge between the ends
      of the cells.
Metaphase
     Chromosomes line up
      in the middle of the
      cell.
     Spindle fibers attach
      to the centromeres of
      the chromosomes.
      (Centromeres hold
      the two identical
      chromatids together)
Anaphase
     Centromeres split.
     The two
      chromatids
      separate and move
      to opposite ends of
      the cell. They
      move along the
      spindle fibers.
     The cell becomes
      stretched out.
Telophase
     Chromosomes
      begin to uncoil
      and loose their
      rodlike
      appearance.
     Two new nuclear
      membranes
      begin to appear.
 Stage 3:
Cytokinesis
       The cell membrane
         
           pinches in around
           the middle of the
           cell.
          The cell divides
           into two new but
           identical daughter
           cells.
          Each daughter cell
           has the same
           number of
          Cytokinesis in Plants
   Cell membrane can’t      A cell plate forms that
    pinch in plant cells.     gradually becomes
                              two cell membranes
                              and then…
                             Cell walls form
                              around the cell
                              membrane.
DNA Replication
        This is the process
         where a cell makes a
         copy of its DNA.
        This happens before
         mitosis occurs.
        Ensures that the
         daughter cells will
         have the right amount
         of DNA.
Structure of DNA
         Looks like a
          twisted ladder or
          spiral staircase.
         It is called a double
          helix. A helix is
          something that
          twists like the
          threads on a
          screw.
Structure of DNA
      cont.
         The sides of the
          ladder are made up of
          sugar molecules
          (called deoxyribose)
          alternating with
          phosphate molecules.
         Each step of the
          ladder (rung) is made
          up of pairs of
          molecules called
          nitrogen bases.
 Structure
continued…
       There are four
              different types of
              bases.
             Adenine (A)
             Thymine (T)
             Guanine (G)
             Cytosine (C)
             A and T pair up.
             G and C pair up.
DNA Replication
   Process sides of the
           
        The two
             DNA ladder unwind
             and separate. The
             base pairs separate
             (like a zipper
             unzipping).
            Nitrogen bases
             floating in the nucleus
             pair up with both
             sides of ladder
             making two new
             strands.