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Question

E. coli cells with a mutated z gene of the lac operon cannot grow in medium containing only lactose as the source of energy because -

A
They cannot synthesize functional beta galactosidase
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B
They cannot transport lactose from the medium into the cell
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C
The lac operon is constitutively active in these cells
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D
In the presence of glucose, E. coli cells do not utilize lactose
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Solution

The correct option is A They cannot synthesize functional beta galactosidase
The Z gene in the structural genes of the lactose operon codes for Beta-galactosidase. A mutation in the Z-gene causes inability in the synthesis of beta-galactosidase.
Hence, lactose cannot be broken down into glucose and galactose.
So, the correct answer is 'They cannot synthesize functional beta-galactosidase'

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