A translational unit in mRNA is the sequence of RNA that is flanked by:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Start codon and the stop codon
A translational unit in mRNA is the stretch of RNA that codes for a polypeptide. It lies between the start codon (AUG) and the stop codon. The mRNA also has untranslated regions (UTRs) before the start codon and after the stop codon. They help translation but are not translated themselves.
(1) Start codon and the stop codon — Correct. The translated stretch is flanked by these two.
(2) Start codon and the untranslated regions — Incorrect. The UTRs lie outside the coding stretch, so they are not its boundaries.
(3) Stop codon and untranslated regions — Incorrect. The UTRs are outside the unit, and the start codon is left out.
(4) Start codon and promoter region — Incorrect. The promoter is a part of the DNA where transcription starts. It is not part of the mRNA.
NCERT Extract:
Translation – …
