DNA is a polymer composed of two complementary chains that form a double helix, and they are composed of a series of units called nucleotides.
Nucleotides are composed of a nitrogen base, a sugar (deoxyribose), and a phosphate group, that attach to each other using the sugar of one nucleotide and the phosphate group of the next.
In the diagram, the steps of the ladder represent the nitrogen bases, while the red and blue ribbons represent the sugar-phosphate backbone.
