Question

The lac operon consists of several genes that encode enzymes required for metabolizing lactose. The expression of the lac operon is regulated by the presence of lactose and glucose.

Q) Describe the regulation operon when the level of glucose is low and the level of lactose is high?

Answer 1

On the major trans regulators of the lac operon is encoded by laci. Four identical molecule of lack protein assembled together to form a homotetraner called a repressive. This repressive bonds to operator sequences adjacent to the promoter of the lack person. Binding of the repressive prevents RNA polymerase from binding to the promoter, therefore the person will not be transcribed, when the operator is occupied by a repressive. Besides it's ability to bind to specific DNA sequences at the operator, another important property of the lack protein is its ability to bind lactose. When lactose is bound to lack the shape of the protein changes in a way that prevents it from binding to the operator. Therefore in the presence of lactose, RNA polymerase is able to bind to the promoter and transcribe the lac operon, leading to a moderate level expression of the lacZ, lacY and lacA genes

A second aspect of lac operon regulation is conferred by a transfactor called cAMP binding protein. When glucose concentrations are low, an enzyme called adinylate cyclase is able to produce cAMP from ATP. The expressions of the lack operon is high, when the glucose is absent and lactose is present. When the glucose is low and lactose is high, CAP and cAMP can bind near the promoter and increase further the transcription of the lac operon. The CAP ( Catabolite Activator Protein) acts as a glucose sensor .It activate transcription of the operon, but only when the glucose levels are low. CAP senses glucose through the hunger signal molecule cAMP as mentioned above.