The chemical structure of DNA and its nucleotides The DNA double helix is composed of two strands of DNA; each strand is a polymer of DNA nucleotides. Each nucleotide consists of a sugar, a phosphate group, and one of four nitrogenous bases. The structure and orientation of the two strands are important to understanding DNA replication. Drag the labels to their appropriate locations on the diagram below. Use only the pink labels for the pink targets, and the blue labels for the blue targets. Labels can be used once, more than once, or not at all.