MITOSIS

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MITOSIS

• DEFINITION
• Division of the Cells Nucleus
• PURPOSE- To ensure that each daughter cell gets
  an exact copy of the chromosomes
• If mitosis goes right- healthy growing organism.
• If mitosis goes wrong- cancer and other diseases
  can develop.

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Why cells must divide...

• List 3 reasons why cells must divide.
• 1 Growth of organism
• While each cell remains tiny
• 2 Repair
• 3 Reproduce

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Chromosomes

• Contain genetic information.
• Made of DNA.
• Numbers of chromosomes per cell
• Humans--46 Total (23 from each parent)
• Fruit fly- 8 total
• Chicken--78
• Not about how complex the organism

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Chromatids

• After replication, the chromosome is composed of
  two identical sister chromatids.
• (Here 2 chromosomes and 4 chromatids)

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Stages of the Cell Cycle
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Time Spent in Mitosis

• The red area shows that a cell spends only a
  small part of its life in mitosis.

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CELL CYCLE
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Interphase

• BEFORE Mitosis
• REPLICATION of chromosomes (S phase)
• Duplication of organelles
• G1 and G2, growth phases. Cell does its normal job

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Prophase

• Chromatids coil into thick rods called
  chromosomes.
• Centrioles appear and move apart.
• Aster appears.
• Nuclear membrane breaks down.

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METAPHASE

• Chromosomes line up along mid-line.
• Chromosomes are moved by spindle fibers attached
  at the centromere.
• Nuclear membrane disappears

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Anaphase

• Separation of Chromosome at Centromere
• Chromosomes move apart.

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Telophase

• Cell membrane pinches in.
• b. Chromosomes reach opposite poles.
• c. Spindle fibers disappear.
• d. Nuclear membrane forms around each
  set of chromosomes.

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Cytokinesis

• AFTER MITOSIS
• Cytoplasm and organelles divide evenly.
• Complete separation--2 cells
• Cytokinesis means cell division
• Mitosis means nuclear division

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Cytokinesis

• Cytoplasmic division
• Animals cleavage furrow
• Plants cell plate

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Which phase is shown?
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Cell Cycle regulationExternal factors

• Growth factors
• Cyclin- Mitosis promoting factor- a protein
  growth factor
• Density-dependent inhibition (Contact inhibition)
• Anchorage dependence

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Cell Cycle regulationInternal factors

• Chromosome check
• Have all the chromosomes replicated?
• Is DNA damaged?
• Mitotic spindle check
• Are all the chromosomes correctly attached to the
  spindle?

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Growth Factors

• G1 Checkpoint (G1/S) External Growth Factors
• Platelet Derived GF (PDGF)- stimulates cell
  division near a wound
• G2 Checkpoint (G2/ M)
• Checks the DNA for damage
• M -spindle checkpoint (before anaphase)
• Checks that the spindle is correctly anchored to
  kinetichore and that chromosomes replicated
  properly

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Meiosis

• Diploid (2n)- Double Chromosome number
• 1 set of chromosomes from each parent
• Haploid (n)- half chromosome number.
• Gamete- Sex cell
• Somatic cell- Body Cell

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Meiosis

• Special Division to produce gametes- sex cells.
• Reduction division
• From one cell, 4 cells may be produced
• Each daughter cell has half the chromosome number
  as the parent.
• The gametes combine to bring the chromosome
  number back to the diploid number.