anticodons

An anticodon is a sequence of three nucleotides in transfer RNA (tRNA) that base-pairs with a complementary codon on messenger RNA (mRNA) during protein synthesis. The anticodon is located in the anticodon loop of the tRNA molecule, with the three nucleotides typically numbered as positions 34–36. By recognizing specific codons, the anticodon helps ensure that the correct amino acid, carried by the corresponding aminoacyl-tRNA, is incorporated into the growing polypeptide chain.

Base pairing between codons and anticodons follows the standard RNA rules: A pairs with U, and G pairs with C. In many contexts, a wobble pair at the 5' end of the anticodon (which pairs with the 3' end of the codon) allows a single tRNA to recognize more than one codon. For example, inosine in the anticodon can pair with A, U, or C. These wobble interactions contribute to the redundancy of the genetic code.

In translation, codon-anticodon recognition occurs in the ribosome's decoding center. The aminoacyl-tRNA synthetase enzymes attach the correct amino acid to each tRNA, and proofreading steps during charging and decoding help maintain accuracy. The anticodon therefore links the genetic information in mRNA to the amino acid sequence of the protein.

Anticodons can be modified post-transcriptionally in tRNA molecules, altering base-pairing properties and translation efficiency. While each tRNA usually carries a single amino acid, some organisms employ tRNAs with modified anticodons to expand codon recognition or to reassign codons in synthetic biology contexts.