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 :- (1) the lac operon is constitutively active in these cells (2) they cannot synthesize functional B-galactosidase (3) in the presence of glucose E. coli cells do not utilize lactose (4) they cannot transport lactose from the medium into the cell.

Answer 1

Dear student,
Answer is 2. They can not synthesize functional B-galactosidase.
z gene for lac operon is mutated due to which the product of z gene which is B- galactosidase is not formed. B- galactosidase coverts lactose into glucose and galactose. Glucose is further utilised as the carbon source by E.coli. Therefore E.coli can not grow in the media containing lactose since it can not be broken down by B- galactosidase.
and source of energy is not available to E.coli.

Regards