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 lac operon encodes for a beta galactosidase protein. This protein is an enzyme that is capable of breaking down the lactose into simpler sugars which can be absorbed by the bacteria. Hence a mutated z gene would result in a non-functional enzyme and thus the bacteria cannot grow.