Wild-type E. coli are grown in four media: (1) glucose only, (2) lactose only, (3) glucose + lactose, (4) no sugar. After 30 minutes, beta-galactosidase activity is measured by a colorimetric ONPG assay (yellow color when cleaved). Higher absorbance at 420 nm indicates more enzyme.
Which medium is expected to produce the highest beta-galactosidase activity?
- A
Glucose + lactose
- B
Glucose only
- Ccheck_circle
Lactose only
- D
No sugar
Explanation
The lac operon is induced by lactose (allolactose) and repressed by glucose via catabolite repression. Lactose alone provides maximal induction with no glucose-mediated repression.