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10 lac operon-2010 update
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10 lac operon-2010 update






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10 lac operon-2010 update Presentation Transcript

  • 1.  
  • 2. Gene Expression
    • constitutive expression – genes which are always turned on
      • known as housekeeping genes
    • induced expression – genes which are only turned on as needed
  • 3. lac Operon
    • lac - lac tose
    • operon – several genes in a sequence all controlled by a single promoter (mainly in prokaryotes; some eukaryotes)
    promoter gene 1 gene 2 gene 3 operator
  • 4. lac Operon
    • Cells mainly use glucose as a source of energy.
    • The lac operon is only turned on when glucose is absent, but lactose is present.
    • lac Operon Animation
    • http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related
  • 5. lac Operon Details
    • Operon codes for 3 enzymes – found in E. coli
    • b-galactosidase ( lacZ gene)
      • enzyme which breaks down lactose
    • permease ( lacY gene)
      • protein transporter which brings lactose into cell
    • transacetylase ( lacA gene)
      • adds acetyl group to galactose
  • 6. Repressor Protein
    • repressor protein ( lacI gene)
      • binds to the operator portion in the presence of glucose.
      • prevents RNA polymerase from transcribing genes when bound to operator
      • transcribed by a different gene from the lac operon
    • When do you want to the repressor to bind / not bind to the operon?
  • 7.
    • When lactose is absent:
      • enzymes are not needed to metabolise lactose
      • repressor binds to the operator to inhibit transcription
  • 8.
    • When lactose is present :
      • lactose binds to the repressor protein
      • lactose-repressor complex cannot bind to the operator
      • transcription can proceed
  • 9. Effector Molecules
    • Since lactose is the molecule that determines when the operon is turned on or off, it is known as an effector molecule.
    • effector molecule – any molecule that can regulate the activity of a protein
    • inducer – effector molecule that binds repressor protein to cause it to fall off operator
  • 10.  
  • 11. lac Operon Animation
    • lac Operon Animation
    • http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related