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Transcription and Translation · USMLE Step 1

Why does the third base of a codon often allow “wobble” pairing, reducing the need for a unique tRNA for every codon?

  1. Because the third codon base is always a guanine or cytosine residue
  2. Because the tRNA anticodon tolerates non-Watson-Crick pairing there
  3. Because the ribosome simply ignores the third base of every codon
  4. Because there are far more sense codons than there are amino acids
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Correct answer: Because the tRNA anticodon tolerates non-Watson-Crick pairing there

The third base of a codon often allows wobble between codon and anticodon, meaning a single tRNA can recognize multiple codons that differ only at the third nucleotide — reducing the number of distinct tRNAs required.

Difficulty: Medium Question 9 of 22

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