Question

What is operon?
A. A set of closely linked genes regulating metabolic pathways in prokaryotes
B. The sequence of three nitrogen bases determining a single amino acid
C. The sequence of nitrogen bases in mRNA which codes for a single amino acid
D. A gene responsible for switching on or off other genes
E. A segment of DNA specifying a polypeptide chain in protein synthesis

Answer 1

Hint:- In a short paper in the Proceedings of the French Academy of Science in 1960, the term "operon" was first proposed. The so-called general theory of the operon was developed from this paper. This theory suggested that in any of the cases, genes within an operon are negatively controlled by a repressor acting on a single operator located before the first gene. It was later discovered that genes could be regulated positively and also regulated in steps following the initiation of transcription.

Complete answer:-
An operon is a functional unit of DNA in genetics that contains a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm or spliced to produce separately translated monocistronic mRNAs. Monocistronic mRNAs are several mRNA strands each of which encodes a single product of the gene. The outcome of this is that either the genes contained in the operon are expressed together or not at all. Eukaryotic genes are not organized into operons, prokaryotic operons are excellent models to understand gene regulation generally. Although there are some gene clusters in eukaryotes that function similar to operons.

From the above information, we can say that the correct option is ‘A’.

Note:- The operon is now simply described as a gene cluster transcribed into a single molecule of mRNA. Nevertheless, in the history of molecular biology, the development of the concept is considered a landmark event. The lac operon in E.coli was the first operon to be described. François Jacob, André Michel Lwoff, and Jacques Monod were awarded the 1965 Nobel Prize in Physiology and Medicine for their findings on the synthesis of operons and viruses.