The one gene-one enzyme hypothesis was postulated by

Given below are two statements:
Statement $I$: In lac operon,the repressor protein binds to the promoter region of the operon and prevents $\text{RNA}$ polymerase from transcribing the operon.
Statement $II$: Regulation of lac operon can also be visualized as regulation of enzyme synthesis by its substrate.
In the light of the above statements,choose the correct answer from the options given below:

In the $lac$-operon model,lactose molecules function as:

During $DNA$ transcription,$mRNA$ is usually single-stranded. However,sometimes an $RNA$ molecule is produced that is complementary to the $mRNA$. This is called ...... and its function is to ...... .

In the $lac$ operon,if a nonsense mutation occurs in the $lac\, y$ gene,which enzymes will be synthesized?

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