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in biology, a unit of three successive nucleotides in a nucleic-acid molecule. In messenger ribonucleic acids (mRNA), triplets form codons, which code the sequence of amino acids in proteins. Certain triplets in the mRNA molecule also determine the beginning (initiatory codons) and end (terminating codons) of the synthesis of polypeptide chains of proteins in ribosomes. In molecules of transport RNA (tRNA), triplets form anticodons. The interaction of a codon with an anticodon triplet of tRNA that is bonded to an amino acid specific for the given codon is a key element in the translation of genetic information. This interaction takes place in accordance with the principle of the complementarity of heterocyclic bases; the interacting triplets form a double helix. The two successive pairs of bases in a codon-anticodon complex are always strictly complementary (Watson-Crick rule), but there may be a deviation from this rule in the third pair (F. Crick’s theory of dissimilar correspondence).
REFERENCEStem, G. Molekuliamaia genetika. Moscow, 1974. Chapters 8, 18. (Translated from English.)
A. A. BOGDANOV
in spectroscopy, a group of three spectral lines that is observed in an atomic or molecular spectrum. Triplets occur upon quantum transitions between triplet levels of atoms and molecules (seeMULTIPLICITY). Triplets are also observed in the normal Zeeman effect.