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Mitosis Low Moments

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					Low Moments In Chicago History:
         The Milly
How Is The Milly Like Mitosis?
   Both are a series of coordinated
movements with the ultimate purpose of
 conveying essential information about
    identity to the next generation
MITOSIS
WHY DO CELLS EVER HAVE TO DIVIDE?
                 Surface Area To Volume




• As the cell increases in size, the volume (cytoplasm) of
  the cell grows faster than the surface area

• With more cell volume to feed, cell is required to do more
  diffusion, but can’t speed up RATE of diffusion

• Cell also cannot excrete wastes via diffusion effectively
             Mitosis (M Phase)
• To ensure a high surface
  area to volume ratio (and
  to reduce the need for
  more DNA), the cell
  undergoes mitotic division

• Mitosis is comprised of
  four subphases;
  prophase, metaphase
  anaphase and
  telophase
                Early Prophase
• chromatin begins to coil
  and condense to form
  chromosomes

• each chromosome
  appears to have two
  strands called a
  chromatid

• each chromatid is
  attached to its sister
  chromatid at the
  centromere
                Late Prophase
• the nuclear envelope and
  nucleolus disappear

• in cytoplasm, the spindle
  apparatus forms

• eventually the spindle
  guides the separation of
  sister chromatids into the
  two daughter cells
METAPHASE
    • spindle grows and
      forms attachments to
      the chromosomes at
      the centromeres

    • chromosomes move
      to an equatorial
      plate which is formed
      along the midline of
      the cell
            ANAPHASE
• centromeres split
• spindle fibers
  shorten, drawing
  the sister
  chromosomes to
  the opposite
  poles
TELOPHASE
    • nuclear
      envelope
      reassembles
    • nucleolus
      reappears
    • chromosomes
      recondense to
      become
      chromatin
                CYTOKINESIS
• in animal cells, a furrow
  appears around the cell
  that eventually pinches
  the cell into two new cells
• in plants, a cell plate
  forms between the two
  daughter nuclei which
  becomes the cell wall
• Since cytokinesis does
  not divide genetic
  material it is NOT a
  mitotic phase
  If cells can undergo mitotic division,
replacing cells with new daughter cells,
             why do we age?
Modeling Mitosis Lab
1. BUILD 4 SETS OF CHROMOSOMES
     1 RED W/10 BEADS, 5 ON A SIDE
     1 YELLOW W/10 BEADS, 5 ON A SIDE
     1 RED W/ 6 BEADS, 3 ON A SIDE
     1 YELLOW W/6 BEADS, 3 ON A SIDE
2.PERFORM THE ACTIONS OF THE S PHASE,
REPLICATING EACH CHROMOSOME
3.JOIN SISTER CHROMOSOMES W/MAGNETIC
CENTROMERE
4. WALK THE 8 CHROMOSOMES THROUGH THE
STEPS OF MITOSIS
5. SHOW THE FINAL GENETIC PRODUCT OF THIS
PROCESS
6. CLEAN UP & RETURN THE BEADS
    Three models of aging
• Oxidative stress

• Glycosylation

• Telomere disintegration
     Model 1: Oxidative Stress
• Free radicals (i.e.
  peroxides) cause
  damage to DNA
• Damaged DNA
  cannot be replicated
  or is replicated with
  mistakes
• Loss of DNA code =
  loss of cellular
  function
   Combating Oxidative Stress
• Antioxidants surround
  and/or remove free
  radicals
• Examples: Fruit, Red
  Wine
Model 2: Glycosylation
           • As cells age, unused
             glucose combines
             with protein and iron
             to create a caramel-
             like substance that
             inhibits cell function
           • Cells cannot divide
Combating Glycosylation
            • Caloric Restriction
            • Studies show that
              individuals who cut
              their caloric intake by
              1/3rd may live 33%
              longer than
              individuals who do not
Model 3: Telomere Disintegration
                 Progeria
• Telomerase may slow
  the loss of cellular
  function due to rapid
  aging caused by the
  genetic disease
  progeria
                How Long?
• Some scientists
  suggest that the
  human body has the
  potential to live for
  200-300 years with
  telomerase therapy
Is Telomerase the fountain of youth?
        Cancer & Telomerase
• Telomerase may be the
  chemical signal that
  allows cells to avoid G0
  and continue to divide
• As cells divide more
  rapidly, they rush
  through G1, G2 and S
  subphases
• Cells reproduce quickly
  but lose function due to
  loss of proper form
MAJOR LIFE EVENTS
Do individual cells have a life history?
The length of the cell cycle varies
         on the species
 Length of cell cycle also depends on
the cell function WITHIN an organism
         Variances In Mitosis
• At any given time,
  different parts of an
  organism may be in
  different parts of the
  cell cycle
• Different organs,
  tissues and structures
  in the body also
  perform mitosis at
  different rates
How do the lengths of the various parts of the
  cell cycle (including mitotic subphases)
    compare? Why are they different?
Lab: Comparative Cell Cycles In
        Allium cepa
Comparative Cell Cycles in Allium cepa

• Purpose: To compare the relative
  proportion of time required to complete the
  cell cycle in two different regions of an
  organism’s anatomy

• Two zones of root growth in Allium cepa
  – Zone of elongation (west side of table)
  – Zone of maturation (east side of table)
Zone of Elongation v. Zone of Maturation
                   Protocol
1. For each lab group, two lab partners will
   assess the zone of elongation, two will assess
   the zone of maturation
2. For each pair, while the other partner tallies
   the results, the other partner should view the
   required region of the slide and classify each
   of the cells in the field of view based on its
   place in the cell cycle
3. Continue until 100 cells have been classified
4. Switch roles and repeat #1-3 for a total of 200
   cells from your zone
                   Analysis
1. Based on your collected results, construct
   two pie charts for the percentage of time
   spent in each of the cell cycle phases
   (interphase, prophase, metaphase,
   anaphase and telophase).
2. In a paragraph, contrast the reasons behind
   the differences. Use the following terms: G1,
   G2, S, G0, zone of elongation, zone of
   maturation, mitosis, anaphase, telophase,
   metaphase, prophase, cytokinesis,
3. Explain the differences regarding the
   function of each subphase and the actions
   in each of the subphases

				
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posted:12/2/2011
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