First slide

Regulation of Gene Expression

Question

Statement A: Lac operon is under control of positive regulation as well.
Statement B: Lac operon is regulated positively by galactose.

Moderate

A

Statements A and B are correct
B

Statement A is correct and B is incorrect.
C

Statement A is incorrect and B is correct.
D

Statements A and B are incorrect.

Solution

Lac operon is under control of positive regulation as well when the glucose concentration decreases. Absence or decrease in glucose concentration promotes the formation of cAMP by activating the enzyme adenylate cyclase. Catabolite activator protein which is inactive becomes active upon binding to cAMP. This CAP- cAMP complex binds nearer to 5ʹ end of promoter and promotes binding of RNA polymerase to promoter and transcription of structural genes is triggered. Neither glucose nor galactose induce lac operon.

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