Somatic Cell Division

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Somatic Cell Division

• Mitosis

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Somatic Cells

• All body cells except gametes (sex cells)

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Somatic Cell Division

• A cell divides into two identical cells
• Replaces dead or injured cells
• Adds new cells for tissue growth

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DNA Replication (Duplication)

• The DNA sequences that make up the chromosomes
  have to be copied so the same genetic material
  can be passed on to the new cells

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Cell Cycle

• The sequence of changes a cell undergoes from the
  time it forms until the time it duplicates its
  contents and divides into 2 cells
• Two major time periods
• Interphase not dividing
• Mitotic Phase - dividing

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Interphase

• The cell replicates DNA and manufactures
  additional cell organelles and cytosolic
  components
• High metabolic activity
• Most growth

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DNA Replication

• DNA nucleotides are synthesized in the cytosol
  and imported to the nucleus
• The helical DNA uncoils and the 2 strands
  separate between the base pairs
• The exposed base pair on each strand pairs with a
  newly synthesized complementary nucleotide
• The new DNA strands take shape as chemical bonds
  form

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DNA Replication - continued

• The original DNA molecule has become 2 identical
  strands of DNA
• Once a cell completes DNA replication, the
  mitotic phase can begin.

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Mitotic Phase

• Mitosis division of the nucleus
• Cytokinesis division of the cytoplasm

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Nuclear Division

• The duplicated chromosomes become divided such
  that one set ends up in each nucleus
• The process is divided into 4 stages
• Prophase, Metaphase, Anaphase and Telophase
• Mitosis is a continuous process and one phase
  merges with the next

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Prophase

• Chromatin fibers condense and shorten into
  chromosomes
• Each prophase chromosome consists of a pair of
  identical double stranded chromatids
• Mitotic Spindle is formed by the pericentriolar
  material and centrioles are pushed to opposite
  sides of the cell
• The nucleolus and nuclear envelope break down

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Metaphase

• The centromeres of the chromatid pairs are
  aligned along the center of the mitotic spindle
  this is called the metaphase plate

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Anaphase

• The centromeres split, separating the chromatid
  pair, which move to opposite ends of the cell.
• Once separated the chromatids are called
  chomosomes.

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Telophase

• Final stage of mitosis
• Begins when chromosome movement stops
• The chromosomes start to uncoil, a new nuclear
  envelope forms, nucleoli appear and the mitotic
  spindle breaks up.
• TWO nuclei are present and the cell starts to
  divide into 2

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Cytoplasmic Division - cytokinesis

• Division of the cells cytosol and organelles
• Begins in late anaphase/early telophase with the
  formation of a cleavage furrow
• Cleavage Furrow slight indentation of the
  plasma membrane

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Checkpoint

• What is the difference between a chromatid and a
  chromosome?
• In which stage of the cell cycle is the cell
  growing?
• What are the mitotic phases in order?
• What is a major event in each stage?