The greatest expression of the lac operon occurs when lactose levels are a) high and glucose levels are low b) low and glucose levels are low c) low and glucose levels are high d) high and glucose levels are high.

The correct answer is a) high and glucose levels are low

Explanation:

Lac operon is an inducible operon which is found in bacteria like E.coli. An inducible operon is the operon which is expressed in the presence of inducer. The inducer binds to the regulatory or repressor proteins, preventing the binding of repressor protein on the operator site thereby trigger gene transcription.

Here the inducer is lactose or allolactose so when lactose is present in high amount it binds to the repressor and allow the transcription of structural gene that are required in the metabolism of lactose.

When glucose is present at a high level in the medium than the lac operon is not expressed and cells use glucose as a primary source of energy. Therefore lac operon expresses more when lactose level is high and glucose level is low.

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