A transcription unit in DNA is primarily defined by:
(A) Promoter
(B) Acceptor
(C) Structural gene
(D) Terminator
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (C) and (D) only
A transcription unit is the stretch of DNA that is copied into one RNA. It has three regions: a promoter, a structural gene and a terminator.
(A) Promoter — Correct. The promoter lies at the start (upstream end) of the structural gene. RNA polymerase binds here, so the promoter marks where transcription begins.
(B) Acceptor — Incorrect. There is no acceptor region in a transcription unit. The word “acceptor” belongs to tRNA, which has an amino acid acceptor end.
(C) Structural gene — Correct. The structural gene lies between the promoter and the terminator. This is the part that is actually copied into RNA.
(D) Terminator — Correct. The terminator lies at the end (downstream end) of the structural gene. It marks where transcription stops.
Note: A similar question was also asked in CUET (UG) 2026 on 29-05-2026 (Slot 1), and in CUET (UG) 2025 on 23-05-2025 (Slot 2) and on 20-05-2025 (Slot 2).
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.”