Which enzyme will be produced in a cell if there is a nonsense mutation in the lac $Y$ gene?

When glucose is the normal energy source in a bacterial cell,which gene transcribes a repressor mRNA?

Why can glucose and galactose not act as inducers for the $lac$ operon?

In the Operon concept,the regulator gene regulates chemical reactions in the cell by:

The functional complex that consists of a cluster of genes including structural genes,a promoter gene,an operator gene,and a regulator gene was discovered by:

An organism is able to survive on a culture medium containing nutrient $A$ through an enzyme-catalyzed process: $A \xrightarrow{X} B \xrightarrow{Y} C$. $A$ mutant organism fails to survive on this medium. However,it grows when nutrient $B$ is added to the medium. Which gene of this mutant is defective?