List the structural genes involved in the digestion of lactose in E coli. Highlight the function of any one. What triggers the transcription of these genes?

• Structural genes are the segments of DNA, which carry codes for the synthesis of proteins. These genes determine the primary structure of a polypeptide chain by having the coding sequence of amino acids in them. For eg, the lac operon of E.coli contains three structural genes, i.e, z, y and a.

(A) Gene z codes for the enzyme beta-galactosidase.

(B) Gene y codes for beta -permease(a membrane-bound carrier protein).

(C) Gene codes for enzyme beta-galactose transacetylase.

Lactose is the substrate for the enzyme beta-galactosidase and it regulates switching on and off the operon.