Anticodon

An anticodon is a trinucleotide sequence in transfer RNA (tRNA) that recognizes a complementary codon in messenger RNA (mRNA) during protein synthesis. It is located in the anticodon loop of the tRNA and is read in the 3' to 5' direction, pairing with the mRNA codon read 5' to 3'. During translation, aminoacyl-tRNA synthetases charge tRNAs with their cognate amino acids by recognizing identity elements that include the anticodon as well as other structural features. Once charged, the tRNA delivers its amino acid to the ribosome's A site, where the anticodon pairs with the corresponding codon, ensuring the correct incorporation of the amino acid into the growing polypeptide chain.

The correspondence between codons and amino acids is defined by the genetic code; because the code is degenerate, wobble base pairing allows certain anticodons to recognize more than one codon for the same amino acid. The wobble position is the first base of the anticodon (the 5' end), which can form noncanonical pairings with the third base of the codon. Modified bases in anticodons, such as inosine, can pair with multiple bases, expanding decoding options and affecting fidelity.

Anticodons are an intrinsic part of tRNA structure and are encoded by tRNA genes. In translation, accurate codon-anticodon recognition is essential for proper protein synthesis and is a central element of translational control and evolutionary conservation.