E. coli are able to break down lactose when present, and this is regulated by the...

E. coli are able to break down lactose when present, and this is regulated by the lac Operon. Describe the mechanisms for the positive and negative control of this operon, and briefly discuss the advantages of both forms of control for this operon.

Expert Solution

Negative control of lac operon

Lac repressor which is synthesised by lacI gene binds to the operator to prevent the binding of RNA polymerase, thus halting transcription of the operon to produce beta galactosidase enzyme to break down lactose. When lactose is present , it binds to the repressor preventing it from attaching to operon and turns on the operon.

Advantage : When lactose is not present or glucose levels are high, there is no need for the enzyme to be produced. The operon is turned off constitutively by the mechanism which saves energy and biomolecules.

Positive control for lac operon.

Even though lactose can act as a positive control, the expression levels are low. Upstream of the promoter has a binding site to CAP ( Catabolite activator protein) when CAP binds , it acts as an activator for transcription ,RNA polymerase binds more effectively.

For CAP to bind this site , it needs to first bind to cAMP which is found in the circulation when glucose levels are low.

Advantages: When glucose is present there is no need to use lactose as an energy source. Positive control helps to increase the amount of beta galactosidase enzymes to break down lactose in the absence of glucose.

gladiator answered 1 year ago

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