Question

E.coli cells with a mutated Z gene of the lac operon can not grow in medium containing only lactose as the source of energy because:

• A. The Lac operon is constitutively active in these cells.
• B. In the presence of glucose, E.coli cells do not utilise lactose.
• C. They cannot synthesise functional β-galactosidase.
• D. They cannot transport lactose from the medium into the cell.

Answer 1

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

Lac Z gene is the structural gene of lac operon in E .coli which synthesis the enzyme (protein) β-galactosidase.
β-galactosidase helps in the breakdown of lactose to glucose and galactose.