X-ray Fibre Diffraction Studies of DNA: Recent Results and Future Possibilities
Much of our knowledge of the three-dimensional structure of naturally occurring and synthetic polydeoxyribonucleotides comes from X-ray fibre diffraction studies of the polynucleotides themselves and X-ray single-crystal studies of nucleic acid bases, nucleosides, nucleotides and oligonucleotides. The degree of crystallinity in the best-defined fibre diffraction patterns from nucleic acids is very high, with reflections extending to spacings of d < 1.5Å (Figure 3.1), indicating that these molecules have very regular three-dimensional structures. For naturally occurring polynucleotides in which there is no particular order in the sequence of adenine (A), guanine (G), cytosine (C) and thymine (T) residues along the polynucleotide chain, the diffraction data indicate that the repeating unit in the structure should be taken to be an average nucleotide. For synthetic polynucleotides with a regular sequence of bases along the polymer chain, the X-ray fibre diffraction data indicate that the structural repeat is typically the chemical repeat. The observation that naturally occurring and synthetic nucleic acids in fibres can assume such highly regular structures has had a profound effect on thinking about molecular mechanisms for the storage, copying and translation of the genetic information.
KeywordsHelix Pitch Nucleic Acid Structure Oriented Fibre Fibre Diffraction Polynucleotide Chain
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