Describe the lac operon, and it's transcriptional control when the concentration of glucose is low, and the concentration of lactose is high.

The lac operon is a section of DNA in E. Coli that consists of a promoter, operator and three genes encoding Beta-galactosidase, lactose permease and another gene. Beta galactosidase is an enzyme responsible for the hydrolysis (allow breakdown) of lactose. RNA polymerase binds to the promoter; and a lac repressor protein binds to the operator, inhibiting the expression of these genes. A regulatory gene encodes the lac repressor protein.When the concentration of glucose is low, and the concentration of lactose is high, lactose binds to the lac repressor protein. This alters the protein structure of the DNA binding site in the lac repressor. Therefore, the repressor can no longer bind to the operator, and RNA plomerase binds to the promoter and carries out transcription.