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Mutagens

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Title: 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
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