MOLECULAR STRUCTURE OF DEOXYRIBONUCLEIC ACID (DNA)

Abstract

K is desirable to keep in mind the limitation of the X-ray method as applied to DNA. Although X-ray diffraction tells that the helical structure is highly regular, and that this structure must hold for lengths of the molecule at least as long as 20 turns of the helix, it does not tell whether this holds for greater lengths, and gives little information about small chemical groups that might be irregularly attached to the helical skeleton. It is probably true, however, that other methods of studying DNA give little suggestion that DNA exists to any large extent in forms other than the double helix, or that irregularities, apart from base sequence, are a dominant feature of its structure.