The redundancy of the code is a consequence of its tripletness and means that one amino acid can be encoded by several triplets (since there are 20 amino acids and 64 triplets). The exceptions are methionine and tryptophan, which are encoded by only one triplet. In addition, some triplets perform specific functions. So, in the mRNA molecule, three of them, UAA, UAH, CAA, are termination codons, i.e., stop signals that terminate the synthesis of the polypeptide chain. The triplet corresponding to methionine (AUG), standing at the beginning of the DNA chain, does not encode an amino acid, but performs the function of initiation (excitation) of reading.
Redundancy of coding sequences is a most valuable property when, since it increases the stability of the information flow to the adverse effects of the external and internal environment. In determining the nature of the amino acid to be incorporated into a protein, the third nucleotide in the codon is not as important as the first two. For many amino acids, the replacement of the nucleotide of the third position of the codon does not affect its meaning.
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