What is the structure of DNA?

The Chemical Nature of Nucleic Acids
• Both DNA and RNA are formed of nucleotides joined together in series. Each nucleotide is composed of a five-carbon sugar, a phosphate group, and a nitrogen-containing base.
• Chargaff's Rule states that in reference to the nitrogen-containing bases, adenine always pairs with thymine, and guanine always pairs with cytosine. Thus, there are always equal proportions of purines and pyrimidines.

The Three-Dimensional Structure of DNA
• Franklin was able to obtain the first glimpse of DNA using X-ray diffraction in 1953, while Watson and Crick theorized that DNA exists in a double-helical, antiparallel configuration.
• Using a spiral staircase analogy, the handrails of the staircase represent the sugar-phosphate backbone of the DNA double helix, and the steps represent the hydrogen-bonded base pairs.