What is a group of genes that functions as a single transcription unit called?

A group of genes that functions as a single transcription unit is referred to as an operon. In prokaryotic organisms, an operon is a cluster of genes that are transcribed together under the control of a single promoter, leading to the production of a single mRNA strand that encodes multiple proteins. This organization allows for the coordinated regulation of genes that are often involved in related functions or pathways, streamlining cellular responses to environmental changes.

Operons are a key feature of bacterial genetics, enabling efficient gene expression and regulation in response to nutritional availability or environmental signals. The idea that several genes can be regulated and expressed together minimizes the energy and resources used by the cell while also optimizing protein production that is needed for specific metabolic processes.

In contrast, polymerase is an enzyme that synthesizes nucleic acids and does not refer to a grouping of genes. Exons and introns relate to the structure of individual genes in eukaryotic cells, where exons are the coding portions of a gene that are expressed, while introns are non-coding regions that are typically spliced out during mRNA processing. Therefore, operons represent a distinct regulatory mechanism not found in the same form in eukaryotes, which separates their gene