X-ray crystallography elastic X-ray scattering include powder diffraction, Small-Angle X-ray Scattering (SAXS) and several types of X-ray fiber diffraction, which was used by Rosalind Franklin in determining the double-helix structure of DNA. In general, single-crystal X-ray diffraction offers more structural information than these other techniques; however, it requires a sufficiently large and regular crystal, which is not always available. These scattering methods generally use "monochromatic" X-rays, which are restricted to a single wavelength with minor deviations. A broad spectrum of X-rays (that is, a blend of X-rays with different wavelengths) can also be used to carry out X-ray diffraction, a technique known
Non-helical models of DNA structure Natural Science, 7, (5), 85-100, 2018. The discovery of topoisomerases, enzymes that can change the linking number of circular nucleic acids and thus "unwind" the replicating bacterial chromosome, was largely seen by the mainstream scientific community to satisfy the topological objection to the Watson–Crick helical structure. The later X-ray crystallography data for the nucleosome, which showed a helical DNA structure wrapped around the protein nucleosome core particle, was considered to provide further affirmation for the existence of the helical structure "in vivo". Non-double-helical models are not currently accepted by the mainstream scientific community. Enzymes capable of unwinding and rewinding DNA