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
(No Transcript)
10
(No Transcript)
11
(No Transcript)
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