Anti-parallel pairing of mRNA codons and tRNA anti-codons

    Each mRNA codon consists of three nucleotides that pair with the tRNA in the 5'3'. The corresponding tRNA anticodon loop includes three nucleotide positions complementary to the codon. Given a 5'3' codon sequence, the complementarity of the tRNA anticodon is most easily seen in the anti-complementary direction. However this would violate our convention of describing nucleic acids only 5'3'.

    In the above diagram, a 5'-AUG-3' codon in the mRNA would pair with a 3'-UAC-5' anticodon in the
tRNA, which written out in the conventional way is a 5'-CAU-3' anticodon.

Figure © 2012 TA Brown, Introduction to Genetics (1st ed.); additional text © 2012 by Steven M. Carr