Mutagens

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Mutagens

• Agents that cause mutations in DNA

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Types of mutations
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Types of mutations
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DNA repair

• DNA in the living cell is subject to many
  chemical alterations.
• If the genetic information encoded in the DNA is
  to remain uncorrupted any chemical changes must
  be corrected- DNA repair

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DNA repair
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Important factors in Cell Cycle

• Normal cells growing will not divide unless they
  are stimulated by one or more growth factors.
• The molecules of growth factor bind to molecules
  of its receptor an integral membrane protein
  embedded in the plasma membrane with its
  ligand-binding site exposed at the surface of the
  cell.
• Binding of a growth factor to its receptor
  triggers a cascade of signaling events within the
  cytosol.
• Many of these involve kinases - enzymes that
  attach phosphate groups to other proteins.
• In most cases phosphorylation activates the
  protein and eventually transfers the signal into
  the nucleus.

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Cell Cycle transduction
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Nucleus

• Here phosphorylation activates transcription
  factors that bind to promoters and enhancers in
  DNA turning on their associated genes.
• Some of the genes turned on by these
  transcription factors encode other transcription
  factors.
• Some of the genes turned on by these downstream
  transcription factors encode cyclins that prepare
  the cell to undergo mitosis.

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Problem

• Genes that participate in any one of the steps
  above can become oncogenes if
• they become mutated so that their product becomes
  constitutively active (that is active all the
  time even in the absence of a positive signal) or
  
• they produce their product in excess (because
  for example their promoter and/or enhancer has
  become mutated)

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Overview
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• http//stream.qtv.apple.com/channels/wgbh/refs/022
  701/nova2805_06_ref.mov