MOLECULAR STRUCTURE OF DEOXYRIBONUCLEIC ACID (DNA)

Although DNA is associated with complex biological phenomena and has many physicochemical properties not easily explained, there is no doubt that the molecule consists to a large extent of the regular, and in some ways simple structure (1-3), derived from x-ray diffraction. We will describe here briefly new data on the structure-the x-ray diffraction measurements and molecular model building being much more exact than in our previous publications (4, 5). The DNA molecule has internal flexibility which enables the helical structure in the solid state to be twisted into either of two well defined configurations or changed reversibly from one to the other, e.g. (6). Proof of the correctness of the structure is doubly convincing because DNA can be studied in these two different forms. This proof resides in the fact that, with a base pairing of the Watson and Crick type (7), the helical structure may be arranged in these two ways, each of which is in agreement with the corresponding diffraction data.