Non-helical models of DNA structure the top of this article, or there could be an equal number of right-handed and left-handed twists, as in the Rodley structure below. The abbreviation "TN", to be used to refer to any DNA structure whose strands are topologically non-linked, has been proposed. The double-helix model of DNA structure was first published in the journal "Nature" by James D. Watson and Francis Crick in 1953 with further details in 1954.) Their work was based upon the crucial X-ray diffraction image of DNA - labeled as "Photo 51" - from Rosalind Franklin in 1952, followed by her more highly clarified DNA
History of molecular biology with the work being done on DNA in the early 1950s. In their seminal 1953 paper, Watson and Crick suggested that van der Waals crowding by the 2`OH group of ribose would preclude RNA from adopting a double helical structure identical to the model they proposed - what we now know as B-form DNA. This provoked questions about the three-dimensional structure of RNA: could this molecule form some type of helical structure, and if so, how? As with DNA, early structural work on RNA centered around isolation of native RNA polymers for fiber diffraction analysis. In part because of heterogeneity