BIO206H5 Lecture 17: BIO206 Lecture 17
Document Summary
There are a number of experimental observations that came to life during the discovery of these regulatory systems. E. g. : e. coli prefers glucose over any other energy source. Lactose only used after glucose has been depleted. Activity of beta galactosidase cleaves bond between glucose and galactose, which make up lactose together. So e. coli in the presence of lactose, but in the absence of glucose produces high levels of beta galactosidase. In the presence of glucose alone, there is very little of the enzyme. This was taken as an indication that this disaccharide lactose was able to modify the way in which genes were expressed in e. coli. So lactose acts as an inducer that can in some way turn on the expression of the beta galactosidase gene. So e. coli can sense the presence of lactose in its environment. No expression often means that the level of expression of that gene is extremely low.
