Question

E. coli 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)

Structural genes and their products in lac operon are as follow:

Lac Z (3063bp): This gene codes for the enzyme $\beta$-galactosidase which breaks operon into glucose and galactose. Therefore, E.coli cells with a mutated Z genes of the lac operon cannot grow in a medium containing only lactose as the source of energy as they cannot synthesize functional $\beta$-galactosidase.