Codons are
triplets of
nucleotides that together specify an
amino acid residue in a
polypeptide chain. Most
organisms use 20 or 21 amino acids to make their polypeptides, which are
proteins or
protein precursors.Because there are four possible nucleotides,
adenine (A),
guanine (G),
cytosine (C) and
thymine (T) in
DNA, there are 64 possible triplets to recognize only 20 amino acids plus the translation termination signal. Because of this redundancy, all but two amino acids are coded for by more than one triplet. Different organisms often show particular preferences for one of the several codons that encode the same given amino acid. How these preferences arise is a much debated area of molecular evolution.
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Although several codons code for a single amino acid, an organism may have a preferred codon for each amino acid. This is called codon bias.
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