Lac Operon System(Catabolite Repression)

1. Lac Operon System
(Catabolite Repression)

2. Lac Operon System
(Turn on & Turn off)
P Lac I Lac I P O Lac Z Lac Y Lac A
Inhibitor
Lactose Allolactose
Lac Inhibitor Promoter
Lactose Catabolism
β-
Galactosidase
Permease
Transacetylase
Polycistronic
RNA
polymerase
Transcription

3. P Lac I Lac I P O Lac Z Lac Y Lac A
Lactose Catabolism
β-
Galactosidase
Permease
Transacetylase
Transcription
When Glucose is absent but Lactose is present
CAP Binding site
CAP
cAMP
CAP cAMP complex
Acts as inducer
RNA
polymerase
Glucose ∝ 1/cAMP
(Concentration)

4. P Lac I Lac I P O Lac Z Lac Y Lac A
Transcription
When Glucose is present and
Lactose is present
CAP
cAMP
CAP cAMP complex
RNA
polymerase
High glucose = Low cAMP (Concentration)

5. Four Situation is possible in
Catabolite Repression
 When Glucose is present but Lactose is absent E. coli does not produce β-Galactosidase.
 When Glucose is present and Lactose is Present E. coli does not produce(or produce a very
little amount of) β-Galactosidase.
 When Glucose is absent and Lactose is absent E. coli does not produce β-Galactosidase.
 When Glucose is absent but Lactose is present E. coli does produce β-Galactosidase.

6. Thank You