The stereochemical code and the logic of a protein molecule

Like DNA and the various forms of RNA, a protein molecule is an information storage system. It contains in fact one or more polypeptide chains which may be regarded as linear sequences of twenty different types of monomer units. It is now clearly established that the chemical information corresponding to a given sequence of a polypeptide chain, containing n amino acid residues, is stored in a segment of one of the two strands of DNA containing 3 n nucleotides. The transfer of such information from a gene to a polypeptide chain takes place according to the well-known process involving a transcription and a chemical translation step. This last step leads to a polymer which, in appropriate conditions, takes a three-dimensional conformation or tertiary structure which should correspond to a free-energy minimum of the molecule and its surrounding water solution.