Which of the following is the substrate for $\beta$-galactosidase?

Which organism was used by Beadle and Tatum to propose the one gene-one enzyme hypothesis?

In the $lac$ operon,which gene is responsible for coding the repressor protein?

The one gene-one enzyme hypothesis was postulated by

The end product of a metabolic pathway binds to the operator to make it more active,so that it can easily bind with the repressor. In this case,the end product is called a/an ......

Which of the following is not a component of the $Operon$ model?