A transcription unit in DNA is defined primarily by the following regions -
(A) Structural gene
(B) A terminator
(C) A promoter
(D) Exon
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (C) only
A transcription unit is the stretch of DNA that is copied into one RNA.
(A) Structural gene Correct. This is the part of the DNA that is actually transcribed into RNA. It sits between the promoter and the terminator.
(B) A terminator Correct. It lies at the 3′ end (downstream) of the structural gene and marks where transcription ends.
(C) A promoter Correct. It lies at the 5′ end (upstream) of the structural gene. RNA polymerase binds to it and starts transcription.
(D) Exon Incorrect. Exons are the coding sequences that remain in the mature mRNA. In eukaryotes the structural gene is split: its exons are separated by introns. An exon is a part inside the structural gene, not one of the three regions that define the transcription unit.
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NCERT Extract:
Transcription Unit –
