The term Double helix (plural helices) describes the structure of DNA as first published by James Watson and Francis Crick in 1953. They showed that DNA is made up of two complementary, antiparallel strands of the bases Guanine, Adenine, Thymine, and Cytosine, covalently linked through phosphodiester bonds. Each strand forms a helix, and the two helices are held together through hydrogen bonds, ionic forces, hydrophobic interactions, and van der Waals forces forming a double helix.