A unit of genetic function common in bacteria and phages, consisting of coordinately regulated clusters of genes with related functions.

• A. Inducible Operon
• B. Operator
• C. Repressible Operon
• D. Operon

Answer: (D)

The main idea is the operon, a unit of transcriptional control in bacteria that groups genes with related functions under a single promoter and coordinated regulatory elements. An operon includes the promoter where RNA polymerase binds, the operator region that a repressor or activator can interact with to turn transcription on or off, and the structural genes that encode the enzymes needed for the pathway. A regulatory gene may produce the repressor that binds the operator, so the whole set of genes is regulated together in response to the cell’s needs. Classic examples like the lac operon (inducible) and the trp operon (repressible) illustrate how this unit can be turned on or off as a whole. The operator itself is just the DNA sequence within the operon that interacts with regulatory proteins, not the entire functional unit. So the description of a unit of genetic function consisting of coordinately regulated clusters of genes with related functions points to the operon.