This is the molecular structure of DNA . A slightly more simplified diagram is shown below.
This image was taken from the Department of Energy's Primer on Molecular Genetics .
The four nitrogenous bases of DNA are arranged along the sugar-phosphate backbone in a particular order (the DNA sequence), encoding all genetic instructions for an organism. Adenine (A) pairs with thymine (T), while cytosine (C) pairs with guanine (G). The two DNA strands are held together by hydrogen bonds between the bases.