1. Describe the structure of DNA. DNA is illustrated by a right handed double helix, with about 10 nucleotide pairs per helical turn. Each spiral strand, composed of a sugar phosphate backbone and attached bases. The DNA is made up of a nucleotides that are bound to each other by phosphodiester bonds. DNA consists of a phosphorous group, and deoxyribose sugar, and a base (Adenine, Guanine, Cytosine and Thymine) Adenine and Guanine are Purines, and the other two are Pyrimidine. The bases are “connected” to each other by hydrogen bonding, A TG C each colon represents the number of H bonds. This structure was first described by James Watson and Francis Crick in 1953.