Structure of DNA

DNA is formed by long chains of nucleotides. Each nucleotide is formed by a phosphate group, a five-carbon sugar (deoxyribose), and a base, which can be adenine (A), guanine (G), cytosine (C), and thymine (T).

Chargaff's rule affirms that the amount of Adenine and Thymine, as well as guanine and cytosine, are always going to be similar.

The chains of nucleotides that form DNA are bound together in spiral shape. Giving it the name of double helix.

In DNA, there is a pattern called complementary base pair, which says that adenine will always bound with thymine, while guanine will always bound with cytosine. 

The two strands of DNA are antiparallel, which means they run in different directions.