Lac Operon System(Catabolite Repression).pptx

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 Lac on +

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)   Lac on ++

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 Lac off 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.

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