Biomolecular structure chemical probing, hydroxyl radical probing, nucleotide analog interference mapping (NAIM), and in-line probing. Protein and nucleic acid structures can be determined using either nuclear magnetic resonance spectroscopy (NMR) or X-ray crystallography or single-particle cryo electron microscopy (cryoEM). The first published reports for DNA (by Rosalind Franklin and Raymond Gosling in 1953) of A-DNA X-ray diffraction patterns—and also B-DNA—used analyses based on Patterson function transforms that provided only a limited amount of structural information for oriented fibers of DNA isolated from calf thymus. An alternate analysis was then proposed by Wilkins et al. in 1953 for B-DNA X-ray diffraction and scattering
Non-helical models of DNA structure helical twists, namely topoisomerases and gyrases, are essential for life, and necessary for DNA replication in various "in vitro" synthesis systems. Non-helical models of DNA structure In the history of molecular biology, non-helical or "side-by-side" models of DNA were proposed in the 1970s as a challenge to the standard double-helical model. The non-helical models attempted to solve problems relating to the topology of circular DNA chromosomes during replication. These theories were briefly considered seriously as a minority viewpoint, but they were later largely rejected due to X-ray crystallography of DNA duplexes and later the nucleosome core particle, as well as