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

Answer 1

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'