The shape of the DNA model was described by James Watson and Francis Crick using an X-ray diffraction image obtained by Rosalind Franklin, known as photo 51, and shared with them by Maurice Wilkins without permission.
This picture determined that the DNA was a double helix with antiparallel strands and that the backbone of the DNA was in the outside of the molecule.
This information, along with previous discoverings, such as:
• DNA is made of nucleotides made of sugar, phosphate, and bases (Levene, 1919)
,
• DNA has an equal number of purines (A+G) and pyrimidines (C+T), (Chargadd, 1950)
allowed Watson & Crick to make their model, in which they describe the structure of the DNA as a double helix with antiparallel strands, paired via complementary base pairs, with the bases in the inside of the helix.
