An operon is a unit of transcription regulated in bacteria. It is structurally a part of the bacterial chromosome formed by a regulatory gene, an operator, a promoter and structural genes.
The lac operon is the regulatory unit that contains the genes involved for lactose metabolism. It is expressed only in the presence of lactose and adsence of glucose. Genes encode proteins that allow bacteria to use lactose as the main source of energy. Two regulatory proteins are involved in the lac operon:
- lac receptor: acts as a lactose sensor.
- catabolite activating protein (actives and stimulates the transcription of the lactose operon genes)
The lac operon cointains 3 genes: lacZ, lacl, lacA. The difference between lacZ and lacl is that lacZ encodes an enzyme that breaks lactose into monosaccharides ( they constitute the simplest form, they cannot be hydrolyzed to a simple one. For example glucose, fructose and galactose) and lacl is a transporter that carries lactose inside the cell.