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Cellular and Molecular Biology

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Mutations in the lac Repressor Protein

CELLS-3Y7EFS

The E. coli lac operon controls expression of several genes that facilitate the hydrolytic breakdown of the disaccharide allolactose (an isomer of lactose) into the monosaccharides glucose and galactose. Glucose can then be used to generate cellular energy in the process of cellular respiration. Review the details of the operon in both the repressed and active states using the figure below.

The lac operon. Top:Repressed, Bottom:Active. 1: RNA Polymerase, 2: Repressor, 3: Promoter, 4: Operator, 5: Lactose, 6: lacZ, 7: lacY, 8: lacA. Raju, T. A. The Lac Operon. Digital image. Wikipedia, 18 May 2012. Web. 4 Feb. 2016. <https://en.wikipedia.org/wiki/Lac_operon#/media/File:Lac_Operon.svg&gt;.

What would be the likely effect of a mutation in the gene for the repressor protein that significantly alters the allolactose binding site?

A

The operon would be active in both the presence and absence of lactose.

B

The operon would be active only in the presence of lactose.

C

The operon would be repressed in both the presence and absence of lactose.

D

The operon would be active only in the absence of lactose.