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. in the presence of glucose, E. coli cells do not utilize lactose
• B. they cannot transport lactose from the medium into the cell
• C. the lac operon is constitutively active in these cells
• D. they cannot synthesize functional $\beta$-galactosidase

Answer 1

Answer: (D)

they cannot synthesize functional $\beta$-galactosidase

Answer 2

The Z gene of the lac operon encodes β-galactosidase, which is the enzyme responsible for breaking down lactose into its constituent sugars, glucose, and galactose. If the Z gene is mutated and cannot produce functional β-galactosidase, E. coli cells will be unable to metabolize lactose, and therefore, they cannot grow using lactose as the sole source of energy.

So, the correct option is (D): they cannot synthesize functional $\beta$-galactosidase