Lecture 16 We are now going to look at ways that genetics can be used to study gene regulation. The issue is how cells adjust the expression of genes in response to different environmental conditions. The principles of gene regulation were first worked out by Jacob and Monod studying the E coli genes required for cells to use the sugar lactose as a nutrient lactose lactose glucose galactose (glucose-galactose) intracellular Lacy (permease) (β- galactosidase) cell mass amount Lacy or lacz lactose time The logic of the Lac operon is that the proteins required to use lactose are only made when their substrate (lactose)is available. This prevents wasteful expression of enzymes when their substrates are notavailable At first, scientists noted that lactose is both an inducer and substrate for the enzymes of the Lac operon and they therefore concluded that lactose was somehow acting as a template for the formation of the enzyme. Then compounds were discovered that could act as inducers but were not themselves substrates for the lac enzymes. The classic example of such a"gratuitous inducer"is IPTG, which is an effective inducer of Lacz expression but isnt hydrolyzed by B-galactosidase IPtG galactose-S-CH CH The existence of compounds such as IPTG shows that recognition of the inducer is a separate molecular event from lactose breakdownLecture 16 Gene Regulation We are now going to look at ways that genetics can be used to study gene regulation. The issue is how cells adjust the expression of genes in response to different environmental conditions. The principles of gene regulation were first worked out by Jacob and Monod studying the E. coli genes required for cells to use the sugar lactose as a nutrient. lactose lactose glucose + galactose (glucose-galactose) intracellular LacY LacZ (permease) (β-galactosidase) log amount + lactose cell mass LacY or LacZ time The logic of the Lac operon is that the proteins required to use lactose are only made when their substrate (lactose) is available. This prevents wasteful expression of enzymes when their substrates are notavailable. At first, scientists noted that lactose is both an inducer and substrate for the enzymes of the Lac operon and they therefore concluded that lactose was somehow acting as a template for the formation of the enzyme. Then compounds were discovered that could act as inducers but were not themselves substrates for the Lac enzymes. The classic example of such a “gratuitous inducer” is IPTG, which is an effective inducer of LacZ expression but isn’t hydrolyzed by ß-galactosidase. CH3 IPTG = galactose—S—CH CH3 The existence of compounds such as IPTG shows that recognition of the inducer is a separate molecular event from lactose breakdown