Which statement best describes an operon? a. several genes, next to each other in eukaryotic DNA, that are transcribed as a single piece of mRNA b. a single gene in prokaryotic DNA that is transcribed as a single piece of mRNA c. several genes, next to each other in prokaryotic DNA, that are transcribed as a single piece of mRNA d. several genes, at different locations in prokaryotic DNA, which are transcribed as a single piece of mRNA

An operon is a functioning unit usually found in prokaryotes. It contains a group of genes under the control of same promoter such that when transcription occurs, these genes are transcribed together to form a single mRNA product. So the genes of an operon are either transcribed together or not transcribed at all. The mRNA formed is usually a polycistronic mRNA i.e. it codes for more than one protein.

Operon has three parts: promoter, operator and structural genes. Promoter enables the structural genes to get transcribed. Operator in turn controls promoter. It's a segment of DNA to which the repressor molecule binds.