Lactose (lac) operon consists of Promoter region, Operator region, Three Structural genes and Repressor or Regulatory gene. The lac operon codes for enzymes which are involved in the degradation (catabolism) of lactose.
Three structural genes are as follows:
1) lac z gene: This gene codes for enzyme b-galactosidase. This enzyme breakdown lactose to glucose and galactose. It also isomerizes lactose to allolactose.
2) lac y gene: This gene codes for enzyme Permease which helps in transport of lactose into cell.
3) lac a gene: This gene codes for enzyme Transacetylase.