Nirenberg and Matthaei experiment another. These experiments helped pave the way for the discovery of the structure of DNA. In 1953, with the help of Maurice Wilkins and Rosalind Franklin’s X-ray crystallography, James Watson and Francis Crick proposed DNA is structured as a double helix. In the 1960s, one main DNA mystery scientists needed to figure out was the number of bases found in each code word, or codon, during transcription. Scientists knew there was a total of four bases (guanine, cytosine, adenine, and thymine). They also knew that were 20 known amino acids. George Gamow suggested that the genetic code was made of
Non-helical models of DNA structure have about 400,000 helical twists in the Watson–Crick model, each of which would have to be removed in as little as 20 minutes, if the strands are to separate during cell replication. This leads to the apparent need of the chromosome - or at least some part of it - to be spinning at speeds up to 6900–9000 rpm throughout the life of the bacterial cell. In 1976, Gordon Rodley and his co-workers published the first non-helical DNA structure, which they named the "side-by-side" (SBS) structure. A similar model was published a few months later by Sasisekharan and his associates.