After the discovery of the structure of DNA in 1953 by Francis Crick, James Watson, Maurice Wilkins and Rosalind Franklin, Gamow attempted to solve the problem of how the order of the four different kinds of bases (adenine, cytosine, thymine and guanine) in DNA chains could control the synthesis of proteins from amino acids.[27] Crick has said[28] that Gamow's suggestions helped him in his own thinking about the problem. As related by Crick,[29] Gamow suggested that the twenty combinations[30] of four DNA bases taken three at a time corresponded to the twenty amino acids that form proteins. This led Crick and Watson to enumerate the twenty amino acids common to proteins. Gamow's contribution to solving the problem of genetic coding gave rise to important models of biological degeneracy.The specific system proposed by Gamow (known as "Gamow's diamonds") was incorrect, as the triplets were supposed to be overlapping, so that in the sequence GGAC (for example), GGA could produce one amino acid and GAC another, and also non-degenerate (meaning that each amino acid would correspond to one combination of three bases – in any order).