The document discusses the operon concept in prokaryotes. It defines an operon as a cluster of genes located together on the chromosome that are transcribed together. Operons contain structural genes whose products work together in a metabolic pathway, as well as a regulatory gene that controls expression of the structural genes. The basic operon structure includes structural genes, an operator site that binds a repressor, and a promoter where RNA polymerase binds. The lac operon codes for enzymes that break down lactose and is induced by the presence of lactose. It contains genes, an operator, and a promoter, as well as the lac repressor gene that produces a repressor protein to block transcription unless lactose is present.