Describe the structure and function of Lac operon.

The gene regulation in bacteria is explained by the operon model. Proteins that are needed for a selected function, or that are involved within the same biochemical pathway, are encoded together in blocks called operons. Lac operon is an example of this that consists of structural genes, promoter, operator, regulator and inducer. The three types of structural genes are z, y and a genes. Promoter is the region where RNA polymerase bind and initiate the transcription of structural genes. Operator is the DNA sequence next to the promoter in which the specific repressor protein binds. Hence, it acts as the switch for transcription. Regulator codes for the repressor protein. Inducer is the substrate that prevent the binding of repressor protein into operator. In Lac Operon, lactose acts as the inducer. If the lactose is absent, the operon is switched off because the repressor protein is produced by the regulatory gene that binds to the operator gene. The lactose inactivated the repressor protein, hence, in the presence of an inducer (lactose), enzymes are produced.