Mitosis

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Mitosis Cell Division
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• All living things start life as a single cell.
• As an organism grows, the cells increase in
  number, not size.

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• The cell grows and eventually splits in two.
• Why are there limits on cell size?

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• 1. The larger the cell becomes, the more demands
  the cell places on its DNA.

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• 2. The cell has more trouble moving enough
  nutrients and wastes across the cell membrane.

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Reasons for Cell Division

• Growth
• Repair
• Reproduction
• Asexual (binary fission)
• Sexual (fusion)

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Surface Area to Volume Ratio

• As the length of a cell increases, its volume
  increases faster than its surface area.

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• This makes it more difficult to move needed
  materials in and wastes out.

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• So, the cell must divide!

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• Mitosis is the process by which the nucleus of a
  cell divides to produce two nuclei.

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• Each nuclei has the same type and number of
  chromosomes that the original cell had.

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• In order to divide, the cell, must follow a cell
  cycle.
• The cell cycle is a continuous process.

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Periods of the cell cycle

• Most cells spend about 90 of their time in
  interphase and about 10 of their time in mitosis
  and cytokinesis.

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• The two main parts of the cell cycle are cell
  growth and cell division.

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• Cell growth interphase - is the longest
  process.
• The cell grows and duplicates the chromosomes.

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Animal Cell

• Interphase

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Plant Cell

• Interphase

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• The second main part of the cell cycle is cell
  division which is called mitosis.

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• The phases in mitosis are prophase, metaphase,
  anaphase and telophase.

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• PMAT Paul made a tower.
• Prophase, metaphase, anaphase, telophase

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PROPHASE
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Animal Cell

• Prophase

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• Prophase is the first stage of mitosis in which
  the nuclear membrane breaks down and the
  chromosomes become short and thick.

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• Individual chromosomes are visible as two
  parallel threads attached at a point called the
  centromere.

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• Each thread is called a chromatid.

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METAPHASE
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Animal Cell

• Metaphase

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• Parallel fibers called spindle fibers appear.
• These attach to each chromosome on either side of
  its centromere.

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• The chromosomes line up at the center or
  equator of the cell.

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ANAPHASE
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Animal Cell

• Anaphase

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• Anaphase is the shortest stage of mitosis and is
  the separation of the chromosomes.

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• The chromatids that were attached to the same
  centromere now separate and move to opposite
  poles of the spindle.

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• Now each structure is considered a separate
  chromosome because it has its own centromere.

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• The chromosomes have been separated into two
  genetically identical nuclei.

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TELOPHASE
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Animal Cell

• Telophase

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• Telophase seems to be prophase in reverse.
• The spindle fibers disappear, a nuclear membrane

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• forms around each of the two sets of chromosomes,
  and a nucleoli appears in each new nucleus.

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• The chromosomes become longer.

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CYTOKINESIS
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Animal Cell

• Cytokinesis

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• The final stage of the division of cells, is
  cytokinesis.

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• Cytokinesis splits the cytoplasm of dividing cell
  into daughter cells.

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• Thanks goes to Prince Georges County Framework
  for Learning website for pictures and information.

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• Mitosis Animations
• Cells Alive

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• How do cells stop dividing?
• When cells come into contact with other cells,
  they stop growing. This is called contact
  inhibition.

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• A protein called CYCLIN regulates the timing of
  the cell cycle.

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Rates of Cell Growth

• Varies by organism and within organism
• Bacteria vs. mammal
• Skin vs. liver
• Dependent upon environmental conditions.

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• What happens if a cell looses control of its
  growth?
• Cancer Cancer cells do not respond to signals
  that control growth.

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CANCER