Which one of the following regions is not a part of transcription unit ?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Inducer
A transcription unit is a stretch of DNA that is copied into RNA. It is defined by three regions: a promoter, the structural gene and a terminator.
(1) Terminator — A region of a transcription unit. It lies at the end of the unit and marks where transcription stops.
(2) Inducer — Not a region of a transcription unit. An inducer is a small molecule, such as lactose in the lac operon, that switches the operon on. It is not a part of the DNA unit.
(3) Promoter — A region of a transcription unit. RNA polymerase binds here to start transcription.
(4) Structural gene — A region of a transcription unit. This is the part that is copied into RNA.
NCERT Extract:
Transcription Unit – “A transcription unit in DNA is defined primarily by the three regions in the DNA : (i) A Promoter (ii) The Structural gene (iii) A Terminator There is a convention in defining the two strands of the DNA in the structural gene of a transcription unit.”
The Lac Operon – “… Lactose is the substrate for the enzyme beta-galactosidase and it regulates switching on and off of the operon. Hence, it is termed as inducer.”