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 utilise lactose.
• B. They cannot transport lactose from the medium into the cell.
• C. They cannot synthesise functional beta-galactosidase.
• D. The lac operon is constitutively active in these cells.

Answer 1

The correct option is C They cannot synthesise functional beta-galactosidase.

The lac z gene is responsible for the production of beta galactosidase which breaks down lactose or allolactose to glucose and galactose. If there is mutation in the lac z gene then there is no formation of beta galactosidase enzyme and there will be no breakdown of lactose or allolactose.