Predict what will happen to the expression of β-galactosidase (lacZ gene) in a mutant strain lacking...

Predict what will happen to the expression of β-galactosidase (lacZ gene) in a mutant strain lacking lacI-gene (cells are not able to produce LacI-protein): A. lacZ gene will not be expressed. B. lacZ gene will be expressed only when both lactose and glucose are present. C. lacZ gene will be expressed only in the presence of lactose; maximum expression will be observed in the absence of glucose. D.lacZ gene will not be repressed; maximum expression will be observed in the absence of glucose. E.lacZ gene will not be repressed; maximum expression will be observed in the presence of glucose.

Expert Solution

Lac operon is a inducible operon which means that presence of a molecule will induce the transcription of the Operon genes. The gene which transcribe the repressor of lac operon is lacl.

Inducer molecule in lac operon is Allolactose which binds to the repressor protein and remove it from the Operon control region and induce the expression of Lac operon in the presence of Lactose (Allolactose is made from lactose).

Now if there's no repressor protein then there's no regulation and it will be expressed continously. But there's one limitation to the expression and that is presence of cAMP and activation of CAP protein which increase the rate of Transcription to its maximum.

Now there's no cAMP or very low cAMP when glucose is present in the cell. So if there's glucose in the cell and the media, there will be very less cAMP and this means that even though lac operon will be active and expressed, the expression levels will not be maximum.

Maximum levels can only be achieved in the ABSENCE of glucose.

So the right option is Option (D) lacZ gene will not be repressed; maximum expression will be observed in the absence of glucose

gladiator answered 2 years ago

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