Bio CH 16 control of gene expression

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  1. How does protein recognize and bind to a specific DNA sequence?
    DNA binding motifs (on protein) (recognize DNA sequence)
  2. Motif:
    • Repeated structure
    • eg: Helix - turn - helix motif
    • eg: Leucine zipper
    • eg: homeodomain
    • eg: zinc finger
  3. Operon:
    • (prokayotes only)
    • -grouping of genes
    • -stretch of DNA used to make enzymes for a particular metabolic pathway
  4. Trp operon:
    • trp - operon make enzyme so cell can make aa tryprotein

    5prime....regulatory region...(operator/promoter)....coding region (5 genes long)...3 prime
  5. Operator:
    where transcription factor attaches
  6. When is operon turned on/off?
    • 1) if tryprophon is absent, cell makes it:
    • RNA polymer binds to promoter and
    • Transcription occurs

    2) If tryptophan is present, operon should turn off
  7. Transcription factor:
    Transcription factor---> Tryptophones attach

    Repressable - strong promoter usually on

    • eg: LAC operon "weak promoter" often off (has to been turned on
    • E. Coli and lactose
  8. Operons:
    • LAC operon - makes enzyme that breaksdown lactose
    • -promoter= weak (generally off) eg E coli.
    • -Needs to be activated to turn on
  9. E. Coli - Cap Protein
    • If (glucose) is low, then bacteria need to use another sugar
    • eg: Lactose

    • If (glucose) is low, then cAMP rises,
    • cAMP binds to CAP
    • and together they bind to DNA

    • If (glucose) is low and (lactose) is high then,
    • Operon is turned on, transcription occurs.

    • If (glucose) is low and (lactose) is low,
    • No transcription
    • (Repressor binds to operator and RNA polymerase cant bind)
  10. CAP:
    Transcription Factor and activator
  11. When glucose is low and lactose is high:
    • some lactose molecules bind the repressor
    • Repressor falls off
    • RNA polymerase binds to promoter
    • Transcription occurs
  12. Glucose and Lactose chart:
    • Glucose +, Lactose + = operon off, CAP is not bound
    • Glucose +, Lactose - = operon off, repressor is bound/cap is not
    • Glucose -, Lactose - = operon off, repressor is bound
    • glucose-, lactose + = operon on, CAP is bound, repressor is not.
  13. Eukaryotes Gene Regulation:
    • 1) more complex
    • 2) Transcription factors - MANY
    • 3) No operons - distant sites on DNA
  14. transcription factors
    • (made of protein)
    • 1) general - on/off switch
    • 2) specific (activators/co-activators)
  15. Activators:
    Modulate rate/speed of transcription
  16. Where does control occur:
    @ transcription initiation site
  17. Control can be either:
    • positive or negative
    • Positive- increases frequency of initiation (activators)
    • Negative - decreases freq. of initiation (repressors)

    both occur on the operator

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Bio CH 16 control of gene expression
2012-03-19 02:08:04

chapter 16 - control of gene expression
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