Watson and Crick Discovered the Structure of DNA In 1953, James D. Watson and Francis H.C. Crick published a paper in which they proposed a model for the physical and chemical structure of the DNA molecule. According to them, most DNA consists of two polynucleotide chains wound around each other in a right-handed (clockwise) helix. In generating their model, Watson and Crick used three main pieces of evidence: The DNA molecule was known to be composed of bases, sugars and phosphate groups. Chargaff's rules says that in any organism, amount of A=T and C=G. Rosalind Franklin, who had taken a X-ray picture of DNA, calculated that DNA was a helical structure which had two distinctive regularities of 0.34nm along the axis of the molecule.  Relating Topics - Overview of Structure of DNA