A transcription unit in DNA is defined primarily by:
(A) A promoter
(B) The structural gene
(C) A terminator
(D) An origin of replication
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (C) only
A transcription unit is the stretch of DNA that is copied into one RNA. It is marked out by three regions.
(A) A promoter — Correct. It lies at the 5′ end (upstream) of the structural gene. RNA polymerase binds to it and starts transcription.
(B) The structural gene — Correct. This is the part of the DNA that is actually transcribed into RNA. It sits between the promoter and the terminator.
(C) A terminator — Correct. It lies at the 3′ end (downstream) of the structural gene and marks where transcription ends.
(D) An origin of replication — Incorrect. This is the site where replication of DNA starts. It belongs to the copying of DNA, not to the transcription unit.
Note: A similar question was also asked in CUET (UG) 2026 on 07-06-2026 (Slot 2), 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.”