Final answer:
An operon in genetics is a functional DNA unit with genes controlled by a single promoter. Operons include structural genes, an operator sequence, and a promoter, but not the regulatory proteins, which are encoded by separate genes.
Step-by-step explanation:
In biology, particularly in the study of genetics and molecular biology, an operon is a functional unit of DNA containing a group of genes under the control of a single promoter. Operons are used to regulate genes in a coordinated fashion in prokaryotes, like bacteria. An operon consists of several key components including two or more structural genes, an operator sequence that is the site of repressor or activator binding, and a promoter sequence where RNA polymerase initiates transcription. A regulatory protein such as a repressor or activator can bind to the operator to control transcription of the genes.
The component not found in an operon is a regulatory protein. Operons include the genes they regulate and the sequences that control their transcription, but the proteins that regulate operons are encoded by separate regulatory genes and are not part of the operon structure itself.