An anticodon is a trinucleotide sequence complementary to that of a corresponding codon in a messenger RNA (mRNA) sequence. An anticodon is found at one end of a transfer RNA (tRNA) molecule. During protein synthesis, each time an amino acid is added to the growing protein, a tRNA forms base pairs with its complementary sequence on the mRNA molecule, ensuring that the appropriate amino acid is inserted into the protein.
Okay, so an anticodon is a three-letter sequence that's complementary, or matches up, to the codon sequence found in the RNA. And the RNA, typically a messenger RNA, codes for proteins. Proteins are made up of amino acids, and these three-letter codons in the RNA are what code for the amino acids to match up with those three-letter codon sequences you need an anticodon sequence to match up with the complimentary bases. And you'll find that anticodon sequence in the transfer RNA, which is carrying the correct amino acid that it's going to attach to the protein that is being generated by that messenger RNA- Elliott Margulies, Ph.D.