Operons Structural gene Operon Polycistronic mRNA Operato

1
Regulation of Gene Expression

• Operons

2
Operon System (bacteria)

• Structural gene
• Operon
• Polycistronic mRNA
• Operator
• Regulator gene
• Repressor

• Overview animation

3
Operon Structure

• PROMOTER---OPERATOR----gene 1gene 2gene 3
• Regulator gene (located elsewhere on
  chromosome)

4
Negative controlshutting something down
5
Inducible Operons

•  Normally OFF, induced (turned on) only when
  needed
•  
• Ex. Lac operon (3 enzymes for catabolism of
  lactose)
• repressor binds at operator no transcription
• lactose binds repressor, comes OFF operator
  Transcription can proceed!

6
This is the graphic from your textbook. I like
the one on the next slide better
7
The lac operon inducible operon
8
The lac operon inducible operon
Inducible operon animation (lac operon)
9
Repressible Operons

• Normally ON, repressed (turned off) when not
  needed
•  
• Example Genes for amino acid biosynthetic
  enzymes
• Arginine operon and tryptophan operon are
  examples.
•  
• Operon is actively transcribing
• Arginine (or tryptophan) is synthesized
• If arginine (or tryptophan) accumulates beyond
  useful levels, arg (trp) acts as COREPRESSOR
• Corepressor repressor protein bind to operator,
  SHUT OFF OPERON

10
This is the graphic from your textbook. I like
the one on the next slide better
11
The trp operon repressible operon
12
The trp operon repressible operon
13
The trp operon regulated synthesis of
repressible enzymes
Repressible operon animation (trp operon)
14
Positive controlramping something up
15

• Activator protein instead of a repressor.
• The activator protein promotes the binding of RNA
  Polymerase to the promoter and thereby acts to
  increase mRNA synthesis.
• Maltose operon is an example

16
Maltose operon
17
Global Control

• Catabolite repression