Regulation of Transcription in Lac Operon

Question 1

Regulation of transcription in lac operon by LACTOSE

Answer 1

Allolactose is an inducer that binds to repressor so it releases DNA

lac repressor binds to operating site, prevents lac mRNA transcription

when lactose is present, it does not repress mRNA transcription, so there is high induced transcription level

repressor-inducer complex does not bind DNA

Question 2

Regulation of trascription in lac operon by GLUCOSE

Answer 2

1. E. coli prefer to utilize glucose (monosaccharide) before breaking-down
   lactose (disaccharide).
2. A protein called Catabolite Activator Protein (CAP) binds to cyclic
   AMP (cAMP) to form cAMP-CAP complexes.
3. cAMP-CAP complexes help to recruit RNA polymerase to the promoter.
4. When glucose is abundant, cAMP levels are low. There are few cAMPCAP complexes. The lac operon have low levels of transcription.
5. However, when glucose is scarce, cAMP levels are HIGH. There are
   many cAMP-CAP complexes. The lac operon has HIGH levels of
   transcription.