Basic structure of Deoxyribonucleic Acid (DNA)

DNA is a double helix of phosphate-sugar strands on the outside, and base pairs of guanine (G) and cytosine (C), and of adenine (A) and thymine (T) on the inside. The base pairs are held together by hydrogen  (H) bonds. Each strand has a 5'-3' orientation, as determined by the sugar component. The two strands run in anti-parallel directions with respect to the=is 5'-3' orientation.