Question

Explain how the lac operon is subject to positive and negative control.

Answer 1

Lac operon can be subjected to positive as well as negative control depending on different conditions..

Positive control

When , lactose is present in the medium the bacteria will have lactose and the lactose will be converted to allolactose and which will bind to the repressor of the lac operon . Repressor normally binds to the promoter regions of the lac operon and inhibit the translation. Allolactose binds to the repressor and makes the repressor inactivated and no binding of repressor to the promoter happens and thus lac operon is transcribed and translated.so, lactose is a positive regulator.

Glucose is a negative regulator of lac operon Because glucose Inhibit cyclic AMP formation .cAMP normally bind with CRP. And makes cAMP-CRP complex which then binds with the promoter and helps the RNA polymerase to bind promoter regions and thus helps in transcription but glucose affect the concentration of cAMP inside cells and thus withdrawn the help of camp-crp mediated help and thus negatively regulates the lac operon.