Read Translation from Codon to Peptide
Translation turns an mRNA codon sequence into a protein. Trace the direction of reading, the tRNA adapter, and the movement through ribosomal sites before choosing an option.
Translation is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Read the coding strand correctly
Divide the mRNA into triplets from the stated reading frame; translate each codon to an amino acid. The resulting peptide is written from its amino (N) end to its carboxyl (C) end. Do not reverse-complement a coding strand as if it were the template strand.
Use tRNA as the adapter
A charged tRNA carries its amino acid at the acceptor end. Its anticodon pairs antiparallel with the complementary mRNA codon. For example, anticodon 3′-AUA-5′ pairs with codon 5′-UAU-3′. Stop codons do not have matching tRNAs; release factors recognise them and terminate translation.
Count arrivals at the ribosome
The initiator tRNA begins in the P site. Each later aminoacyl-tRNA enters the A site before its amino acid is added. A peptide of n amino acids therefore needs n−1 A-site tRNA arrivals; for 90 amino acids, count 89. The P and A sites position the growing chain and the incoming amino acid for peptide-bond formation.
Locate the inhibited or catalysed step
Ribosomal peptidyl transferase activity catalyses peptide-bond formation between the growing chain and the A-site amino acid. Charging tRNAs beforehand invests energy that helps drive this reaction. Streptomycin targets the bacterial small ribosomal subunit: among the listed question choices, the earliest affected initiation event is mRNA binding to the ribosome. Splicing belongs to RNA processing, not translation.
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- ✓Coding DNA → mRNA: keep 5′→3′ order, change T to U; then read triplets.
- ✓Anticodon pairs antiparallel with codon; amino acid attaches at the tRNA acceptor end.
- ✓Stop codons recruit release factors, not matching tRNAs.
- ✓Initiator starts in P; later tRNAs enter A; n amino acids need n−1 A-site arrivals.
- ✓Peptidyl transferase makes the peptide bond; RNA splicing is not translation.
First identify whether a DNA strand is coding or template. Then keep codon and anticodon directions visible; this prevents reversing a peptide, assigning tRNAs to stop codons, or counting the initiator as an A-site arrival.
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