Question

The messenger RNA formed in lac operon model from the structual genes is

• A. Monocistronic
• B. Dicistronic
• C. Polycistronic
• D. All of the above

Answer 1

Answer: (C)

Polycistronic

A cistron is a gene which is made up of DNA and carries instructions to make proteins. Polycistronic mRNA molecule (e.g., the mRNA encoded by the trp operon) carries the coding region for several proteins and thus is transcribed from more than one genes. These proteins function together in a biological process. Polycistronic mRNA is usually seen in bacteria. Most eukaryotes have monocistronic mRNA molecule that encodes a single protein. The lac operon is an operon responsible for transport and metabolism of lactose in Escherichia coli and other bacteria. It has three structural genes (lac Z, lac Y, and lac A) regulated by a single promoter and when these genes are transcribed a single polycistronic mRNA is formed. The mRNA produced by transcription carries information for the synthesis of all three proteins.Hence, it is a polycistronic mRNA. Thus, the correct answer is option is C.