The GATE Grind

GATE 2026 BT – Question 42

Genetics, Cellular and Molecular Biology · Molecular Biology: Replication, transcription, splicing, translation, non-coding and micro RNA, RNA interference, DNA damage and repair · 2 marks · Multiple select

Messenger RNAs (mRNAs) translate to generate polypeptides and the translation terminates at the UGA, UAG or UAA stop codons. The AGA codon acts as additional stop codon in the mitochondria. The longest possible polypeptide(s) that can be hypothetically translated in the cytosol and/or mitochondria, from the given full length mRNA sequence (36 nucleotides) is/are

5'-AACACCAUGACCCAUGUGGCGAGACGGUAGUUAAAA-3'

  1. 7 amino acids long in the cytosol
  2. 5 amino acids long in the mitochondria
  3. 6 amino acids long in the mitochondria
  4. 8 amino acids long in the cytosol

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Show answer and explanation

Correct answer: (A) 7 amino acids long in the cytosol; (C) 6 amino acids long in the mitochondria

Explanation

There are two AUG start codons. The first, AUG ACC CAU GUG GCG AGA CGG UAG, gives 7 amino acids in the cytosol (stop at UAG), but only 5 in the mitochondria because AGA is a stop there. The second AUG (inside CCCAUGUGG), AUG UGG CGA GAC GGU AGU UAA, has no stop until UAA and gives 6 amino acids in both. So the longest is 7 in the cytosol and 6 in the mitochondria.