These are segments of DNA that carry codes for the synthesis of proteins.
These have different components- structural genes, operator genes, promotor genes, and regulatory genes.
The structural gene determines the primary structure of a polypeptide chain by having the coding sequence of amino acids in them. For example- The lac operon in E.coli contains three structural genes,i.e. Z, Y, and A.
Gene-Z:
It contains 3063 base pairs and codes for the enzyme beta-galactosidase,
This enzyme breaks lactose into glucose and galactose.