Multiple choice

Which of the following amino acids is coded by UAG?

  1. Methionine

  2. Lysine

  3. Pyrrolysine

  4. Glutamine

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

UAG is typically a stop codon, but in certain archaea and bacteria, it codes for pyrrolysine, the 22nd proteinogenic amino acid. Pyrrolysine is used in methane-producing metabolism by some organisms.