Unit 2B Mitosis

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Unit 2B - Mitosis

• Section 2 Mitosis

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What is mitosis?

• Cell Division
• Creation of two daughter cells
• Cells are genetically identical.
• Occurs in eukaryotes
• Replaces somatic cells
• Some cells do not divide
• Skeletal
• Nervous
• RBC

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Mitosis in Eukaryotes

• Eukaryotes use mitosis to produce identical
  daughter cells by means of asexual reproduction
• Complex process involving cytoskeletal systems
• Linear DNA strands separated by complex motor
  systems
• Eukaryotes use meiosis to produce a new mix of
  genes by means of sexual reproduction.
• Meiosis similar to mitosis but different in
  detail
• Usually occurs when a cell gets too large

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Cell Division in Prokaryotes

• Prokaryotes undergo simple fission to produce
  identical daughter cells asexual reproduction.
• No mitotic spindle (they have no cytoskeleton)
• Single circular DNA molecule separates as the
  cell wall separates the new cells
• Prokaryotes do have sex hence they do not
  undergo meiosis

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Mitosis

• Interphase
• G1 Phase Cell Growth
• S-Phase DNA Replication
• G2 Phase Preparation for Mitosis
• Cell Division
• Prophase
• Metaphase (Early and Late)
• Anaphase (Early and Late)
• Telophase
• Cytokinesis

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The Eukaryotic Cell Cycle

• Usually takes between 8 10 hours to complete a
  cycle.

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Interphase

• G1 Gap 1 Phase
• Cells are actively growing
• They are making biological compounds, like
  enzymes to be ready to undergo DNA Replication.
• If a cell does not divide, this is the place that
  the cell becomes stuck, it is typically noted
  as G0
• S
• DNA Replication occurs Synthesis of DNA
• Creation of X - Chromatids
• G2 Gap 2 Phase
• Increased rate of protein synthesis occurring.
• Cell is preparing for division.
• Fairly short compared to G1 and S phases

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What will it look like?
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Prophase

• Longest phase of the mitosis cycle.
• Chromosomes are visible under a microscope.
• Chromatin condenses into a chromosome to make
  sure it does not become tangled.
• Sister chromatids are bound by a centromere
  (which is a special protein that holds the
  chromatids together.
• Centromeres develop kinetochores to which a
  spindle fiber (microtubule) will attach
  eventually.
• Centrioles begin to move to the ends of the
  cells, called the poles, they were near the
  nucleus. (This gives direction to the cell,
  allowing the identification of an equator).

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Prophase

• The MTOC (microtubule organization center) is
  found around the centrioles, which helps direct
  the microtubules.
• Plants
• Have microtubules that are hard to see.
• Animals
• Have centrioles at the MTOC which are surrounded
  for protection.
• Nucleus disappears
• Nuclear Envelope breaks down.
• Sister chromatids become attached to
  kinetochores, which are attached to the
  centromere.

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Prophase Cont
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Metaphase

• Chromosomes line up at the equator of the cell.
• This is the best time to photograph chromosomes.
• Polar microtubules extend from the pole to the
  equator and overlap.
• Kinetochore microtubules extend from the
  centrioles to the centromere area.
• They will pull the chromatids apart later.
• Early and Late metaphase

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Anaphase

• Chromosomes are pulled toward the poles /
  centrioles.
• The kinetochore microtubules pull apart the
  chomatids so the chromosomes go to different ends
  of the cell.
• Form V or A as they pull.

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Telophase

• The cell returns to similar conditions as in
  interphase.
• The nuclear envelope, nucleolus reappear and the
  chromosomes begin to unwind.
• The cell will begin to split into two.

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Cytokinesis

• This is the actual formation of two cells.
• Animal Cells Cleavage Furrowing
• Actin filaments begin to encircle the equator
  region and pinch the cell into two by tightening.
• Eventually the cell membranes touch and split to
  give two cells.
• Plant Cells Cell Plating
• The golgi apparatus releases vesicles that
  contain carbohydrate molecules.
• The vesicles line up along the equator and begin
  to form the cell membrane, primary cell wall and
  middle lamella.

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Telophase Cont
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Mitosis
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Plant Cell Mitosis
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Onion Cells under Microscope
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Onion Cells under Microscope
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Onion Cell Mitosis - Red Stain
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Onion Cell Mitosis
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Onion Cell Mitosis
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Onion Cell Mitosis - Red Stain
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Onion Cell Mitosis - Red Stain
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Animal Mitosis
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Animal Cell Mitosis
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Animal Cell Mitosis
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Animal Cell Mitosis
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Chromosome Structure
G1
G2
M Mitosis
G1
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Cell Division Regulation

• Depends on pH, temperature, nutrition and type of
  cell.
• If optimal conditions, the cell will undergo
  mitosis quicker than in problematic conditions.
• Checkpoints are built into the cell cycle to
  ensure accuracy of the process.
• Protein Kinases are enzymes that control
  phosphorylation
• Cyclin-dependent kinases (Cdk) control the cell
  cycle. This protein regulates when the cell can
  continue into the phases of mitosis.

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Cdk examples

• Prepares the cell for S phase and allows it to
  enter S phase.
• MPF Mitosis Promoting Factor Prepares the
  cell to enter prophase.
• Activates the Anaphase Promoting Complex (APC)
  which allows proteins to start to break down that
  hold the chromatids together so they can be
  allowed to separate.
• This is still new research and is considered
  cutting edge at this time.
• Why important? - Drugs
• Knowing this allows the creation of drugs to
  prevent the high rate of cell division in cancer
  patients.

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MPF, Cyclin, and Cdk