Final answer:
An operon is a segment of DNA in prokaryotic cells that includes genes for related proteins, a promoter, and an operator, facilitating the regulation of entire metabolic pathways. Operons allow for coordinated gene expression, responding to environmental changes efficiently, as seen in the LAC operon's response to lactose availability in bacteria.
Step-by-step explanation:
A stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins, which typically facilitate an entire metabolic pathway, is known as an operon. In prokaryotic cells, operons are essential for the regulation of gene expression, grouping genes of related function that are transcribed together under the control of a single promoter and operator. The LAC operon is a well-studied example that controls the metabolism of lactose in bacteria such as E. coli. This operon includes genes coding for proteins like beta-galactosidase and a permease that are crucial for utilizing lactose.
The promoter sequence is located upstream of the coding genes and is the site where RNA polymerase initiates transcription. The operator sequence situated between the promoter and coding genes acts as a binding site for repressor proteins that regulate the transcription process. When specific conditions trigger these regulators, the genes within the operon can be turned on or off, efficiently controlling the production of proteins associated with various metabolic pathways, like the synthesis of the amino acid tryptophan in the trp operon.
Operons streamline the regulation of gene expression, providing a mechanism for bacteria to quickly respond to environmental changes. For example, with the presence of lactose, the LAC operon becomes active, allowing the bacterium to metabolize the sugar efficiently. In the absence of lactose, the operon is repressed, conserving the organism's resources.