Inducible Operon: Lac Operon
The lac operon is a classic example of an inducible operon in bacteria. This operon consists of three genes - lacZ, lacY, and lacA - that encode proteins involved in the metabolism of lactose. The expression of these genes is controlled by a regulatory region that includes the lac promoter and the lac operator.

Inducible Operon
An inducible operon is one that is normally turned off but can be turned on in the presence of a specific inducer molecule. In the case of the lac operon, the inducer molecule is lactose. When lactose is present in the environment, it is converted into allolactose, which binds to the lac repressor protein. This binding prevents the repressor from binding to the operator region, allowing RNA polymerase to transcribe the genes of the lac operon.

Regulation of Lac Operon
The lac operon is under both positive and negative control. The lac repressor protein binds to the operator in the absence of lactose, preventing the transcription of the lac genes. However, in the presence of lactose, allolactose binds to the repressor, causing a conformational change that releases the repressor from the operator. This allows RNA polymerase to bind to the promoter and initiate transcription of the lac genes.

Conclusion
In summary, the lac operon is an example of an inducible operon because it is normally turned off but can be turned on in the presence of lactose. This regulatory mechanism allows bacteria to efficiently metabolize lactose when it is available in their environment.