Identify the pieces of evidence describing the features of DNA that Watson and Crick used to determine the structure of DNA. The sugar-phosphate backbones of each DNA helix run antiparallel to one another. The nitrogenous bases on each DNA helix are arranged perpendicularly to the central axis. 0 A 1:1 ratio of purines to pyrimidines is present in a DNA molecule, with A pairing with C and G pairing with T. A purine base forms hydrogen bonds to pair with a pyrimidine base located on the opposite DNA strand. Specifically, A pairs with T, and C pairs with G. The diameter of the DNA double helix is 2 nanometers, with each purine-pyrimidine base pair spanning an equivalent distance between the two chains. The two chains are parallel, both running in a 5' to 3' direction.