Mitosis

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Mitosis

• The Life and Times of the Cell

2
Objectives

• List factors that influence when cells divide
• Understand describe the Cell Cycle
• Study the events of cell division (Mitosis)
• Compare Mitosis in plant animal cells
• Cell Division Animation

3
Reading Assignment

• Read Section 10-1, p.241-243 titled Cell Growth.
• From the diagram indicating the Ratio of Surface
  area to Volume onp.243, sketch in your notes the
  smallest cell and the related statistics for
  Surface Area, Volume, and Surface Area to Volume
  Ratio and then sketch the largest cell with its
  related statistics.
• Answer the 4 questions in 10-1 Section Assessment
  on p.243.

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Cell Cycle 4 Phases

• Gap 1 (G1)
• Typical cell growth metabolism.
• S Phase (S)
• DNA Replication
• Gap 2 (G2)
• Centrioles Replicate
• Protein synthesis
• M Phase (M)
• Mitosis phase / cell division occurs

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Cell Cycle

• The G1, S and G2 stages of the Cell Cycle happen
  during INTERPHASE.
• The M phase consists of Prophase
  Metaphase Anaphase Telophase Cytokinesis

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S Phase - DNA Replication

• An enzyme called Helicase causes the hydrogen
  bonds that hold DNA together to break or unzip
• Then DNA Polymerase allows free floating
  nucleotides to attach to the single strand of DNA
• DNA is Replicated

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• Replication
• DNA Replication..Who wants to try?
• Replication Song

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Draw DNA Replication

• Draw a DNA triplet with the base sequence ATG on
  the left side. Make the 5 the top left.

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DNA Replication

• Separate the original DNA strands.
• With different colors, show the attachment of
  free-floating nucleotides.

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DNA Replication

• Where do the free-floating nucleotides come from?
• Foods we eat!
• How do the 2 strands compare?
• They are exactly the same!
• What happens if there is a mistake made during
  replication?
• A mutation occurs!

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M Phase Mitosis (4/5 Phases)

• 1. Interphase
• G1, S, G2 phases
• 2. Prophase
• Early Late
• 3. Metaphase
• 4. Anaphase
• 5. Telophase
• Early Late
• Cytokenesis

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Interphase
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Early Prophase

• Replicated centrioles split and start moving to
  opposite sides of the cell forming ASTERS.
• Nuclear envelop disappears
• Replicated chromatin shortens, thickens and forms
  CHROMATID PAIRS

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Remember this Diagram?
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Early Prophase
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Late Prophase

• Centrioles have reached opposite poles of the
  cell
• SPINDLE forms
• Chromatid Pairs float throughout the cytoplasm.

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Late Prophase
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Metaphase

• Shortest stage of Mitosis
• Chromatid pairs align at the equator of the
  spindle

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Metaphase
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Anaphase

• Chromatid pairs split
• Spindle fibers contract and the single
  CHROMOSOMES are pulled to opposite poles

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Anaphase
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Early Telophase

• Often described as the opposite of prophase
• Nuclear envelop reappears
• The chromosomes unravel to become chromatin
• Cleavage furrow begins to form

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Late Telophase

• Cleavage furrow completes its indentation.
• Mother cell splits into 2 identical Daughter
  cells in a process called CYTOKINESIS

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Early/Late Telophase
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Summary of Mitosis

• Prophase
• Replicated chromatin condense into chromatid pair
• Centrioles move to opposite poles
• Nuclear envelope disappears
• Spindle fibers start to form
• Metaphase
• Chromatid pairs line up at the equator
• Anaphase
• Chromatid pairs split
• Chromosomes are pulled to opposite poles by the
  spindle fibers
• Telophase
• Chromosomes de-condense into chromatin
• Nuclear envelope reappears
• Cytoplasm is divided into 2 cells
• Cytokenesis

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Mitosis

• I don't watch television when I can talk about
  Cell Division!

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One more Phase GAP 0 (G0)

• Some cells do not replicate their centrioles
  during Prophase.
• They lose their ability to divide
• They enter the Gap 0 stage
• Neurons of the Spinal cord / Brain cells

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Mitosis in Plant vs. Animal CellsThe Rivalry
Continues

• Plants have no centrioles but still form spindle
  fibers
• Plant cells divide from the inside out
• Cell Plate
• Messy Metaphase

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Plant Cell Mitosis
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Importance of Mitosis

• Method of reproduction for all single celled
  organisms
• Allows us to regenerate cells (tissue) repair
  cuts, bone breaks, etc
• Growth one cell to trillions

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How Long does the Cell Cycle Last?

• Pick up a textbook and turn to page 249.
• Read the section titled Life Spans of Cells and
  answer the 4 questions that follow.

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Regulating the Cell Cycle

• Turn in your textbook to page 250. Read pages
  250 to 252.
• Answer the 5 questions that follow.
• Terms Contact Inhibition Cyclins Internal
  regulators External regulators Cancer

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Meiosis

• Special cell division that produces Haploid sex
  cells
• Consists of one replication and two cell divisions

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Sexual vs. Asexual

• Asexual Reproduction

• Sexual Reproduction

• Reproduction that doesn't involve sex cells
• Produces clones of previous cells
• Ex 1. Binary Fission
• 2. Fragmentation
• 3. Budding

• Reproduction involving sex cells
• Produces genetically different offspring
• Sperm egg Zygote
• (n) (n) (2n)

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Cancer

• A disease of uncontrolled cell division
• Starts with a single cell that loses its control
  mechanisms due to a genetic mutation (mistakes in
  DNA replication)
• Can be caused naturally or by carcinogens (i.e.
  tobacco smoke, chemicals, etc.)
• That cell starts dividing without limit, possibly
  killing the host (without treatment)

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Cancer Treatment

• Three basic treatments
• Surgery to remove cancer
• Radiation to kill affected cells
• New drugs are becoming available (Chemotherapy)
• It is hard to remove cancer (tumors often lack
  clear boundaries)
• Some tumors are very small and are found
  throughout the body (advanced stages)
• Radiation and chemotherapy are aimed at killing
  cancer cells
• The body then has to replace those dead cells
  which requires a lot of energy
• Therefore treatment must be balanced with overall
  patient health
• Unfortunately due to natural selection cancer
  that seems to have disappeared can come back in
  the future in a form that is resistant to the
  radiation / chemotherapy
• Using multiple drugs can decrease the risk of
  relapse
• Multiple drugs decrease the probability of cells
  acquiring immunity