This paper was revolutionary at the time because no one had been able to establish a plausible
structure for DNA. Even the
great Linus Pauling who had determined the
structure of the alpha-helix, was unable to do so. Crick and Watson mention that Pauling had provided them with a copy of their manuscript before publication. This allowed both of them to compare his model to theirs and pinpoint its inconsistencies. Pauling's model had the phosphate groups
facing the interior of the DNA structure with the bases on the outside. If the phosphate groups were "naked" and charged, there would be a tremendous repulsion between the negatively charged groups,breakingapart"the three intertwined chains" that Pauling postulated existed. Crick and Watson emphasized that their DNA molecule was in the salt form. If the DNA was in its free acid form, the acidic hydrogensmay interact with enough affinity to hold the structure together. However, in the salt form, no hydrogens would be present.
Crick and Watson had built a model of DNA based on their interpretation of the X-ray diffraction pattern obtained orginally by Mrs. Rosalind Franklin, a few years before. Their model had two right-handed helical chains, twisting around a vertical axis with the bases on the inside, facing each other and the phosphates on the outside, interacting with solvent molecules and cations. The horizontal plane formed by the facing base pairs would be perpendicular to the vertical axis. Each chain would consist of Beta -D-deoxyribofuranose residues joined at 3', 5' linkages with a base sequence running opposite to the facing chain sequence. In other words, the chains would be anti-parallel 5' to 3' and 3' to 5'. They calculated, based on their model, that one residue would be present "every 3.4 Angstroms in the z-direction". Crick and Watson also addressed the presence of water molecules and their abundance, concluding that the DNA molecule they were dealing with, had a high water content due to its opened structure. The same DNA molecule would undergo structural changes as the water content would diminish, they predicted. This observation was the basis of the differences between B-DNA and A-DNA structures.
Next, their modelpredicted the nature of the base-base interactions as hydrogen bonds. These bonds would exist in the assumption that the bases would take on the most stable keto tautomeric form, allowing a specific hydrogen bonding pattern to exist only between certain bases: Adenine with Guanine and Cytosine with Thymine. Using Chargaff's rule that stated that there was an equimolar concentration of A, T, G, C, they defined once and for all the rules of base pairings.
Their final interestinginsight was that the base sequence and pairing would be involved in the transcription of the genetic material of DNA. This was just the beginning of more discoveries to come about transcription and translation ofgenetic materialinto functional proteins.