DNA double helix

View of a short piece of a DNA double helix. This is a molecular model generated from X-ray diffraction data. Carbon atoms are shown in black on one strand and white on the other. Nitrogen atoms are in blue, oxygen atoms in red and phosphorus atoms in purple. Hydrogen atoms are not shown. This is the standard double helical "B" form of DNA solved by Watson and Crick. The two sugar phosphate backbones are linked by the interaction of the base pairs - C with G and A with T. This piece is approx. 25 bp long.