NEET2005ZoologyMolecular Basis of InheritanceActual
E.coli cells with a mustard z gene of the lac operon cannot grow in medium containing only lactose as the source of energy because:
Options
- Athe lac operon is constitutively active in these cells
- Bthey cannot synthesize functional galactosidase
- Cin the presence of glucose, E.coli cells do not utilize lactose
- Dthey cannot transport lactose from the medium into the cell.
Correct answer
B. they cannot synthesize functional galactosidase
Step-by-step solution
The z gene in the lac operon encodes for a 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. Related Theory Glucose is the preferred and most frequently available energy source for E. coli. The enzymes to metabolize glucose are made constantly by E. coli. When E. coli is exposed to both lactose and glucose, the organi