Q. 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 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 β-galactosidase
Explanation
[Solution from source] The z gene codes for β-galactosidase, which splits lactose into glucose and galactose. Without a working enzyme, lactose cannot be used for energy. Lactose transport depends on permease, the y gene product, so the transport option describes a y mutation instead. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.