Final answer:
One promoter and one operator managing three structural genes in the lac operon allows for efficient energy use and synchronized gene expression, producing necessary enzymes only when lactose is available for metabolism in the cell.
Step-by-step explanation:
The advantage to having one promoter and one operator associated with three structural genes that produce lactose metabolizing enzymes, like those found in the lac operon, lies in the efficiency and coordinated regulation of gene expression. This setup allows the bacterial cell to conserve energy and resources by only producing the enzymes when lactose is present and needs to be metabolized.
When lactose is absent, a repressor protein binds to the operator, blocking RNA polymerase from binding to the promoter, thereby preventing expression of the lac genes. Conversely, when lactose is present, it binds to the repressor, causing it to release from the operator. This change allows RNA polymerase to access the promoter and transcribe the genes, leading to the production of the enzymes required for lactose digestion: beta-galactosidase, galactoside permease, and thiogalactoside transacetylase.
The lac operon model is a prime example of gene regulation, demonstrating how cells can efficiently respond to environmental changes. This model has also been foundational in understanding the principles of gene regulation in both prokaryotes and eukaryotes.