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The Operon

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Repressor can't bind to operator when Arg is lacking. Maltose Mechanism. Maltose acts as an inducer when present. RNA poly is able to recognize binding site ... – PowerPoint PPT presentation

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Title: The Operon


1
The Operon
  • Focusing on the Promoter Sequence

2
Regulation
  • Gene expression
  • Transcriptional
  • Repression or Induction
  • Eukaryote vs Prokaryote

3
Operon Model
  • Activator Binding Site
  • Promoter
  • RNA polymerase
  • Operator
  • Gene products

4
Promoter sequences
  • promote the recognition of transcriptional start
    sites by RNA polymerase
  • Sigma factor proteins
  • -35 position Consensus sequence (TTGACA)
  • -10 position Pribnow box (TATAAT)

5
Repression / Induction(negative positive)
6
Repression of Arginine Synthesis
  • Arginine acts as a corepressor
  • Repressor cant bind to operator when Arg is
    lacking

7
Maltose Mechanism
  • Maltose acts as an inducer when present
  • RNA poly is able to recognize binding site

8
Lactose Operon
9
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10
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11
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12
Tryptophan Operon
13
Comparison
  • Lac Operon
  • Enzyme induction
  • Catabolic rxn
  • Regulation by substance (lactose)
  • For gene expression to occur (presence of
    lactose)
  • Trp Operon
  • Enzyme repression
  • Anabolic rxn
  • Regulation by substance (tryptophan)
  • For gene expression to occur (absence of
    end products tryptophan)

14
Regulation of trp operon
  • Regulated in two ways
  • Repression (negative control)
  • Attenuation

15
Repression
  • If there is no trp
  • TRANSCRIPTION PROCEEDS
  • However..
  • If there is excess trp
  • TRANSCRIPTION BLOCKED

16
Attenuation
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