DNA is a linear polymer made up of four different monomers. It has a fixed backbone from which protrude variable
substituents (Figure 1.1). The backbone is built of repeating sugar-phosphate units. The sugars are molecules of
deoxyribose from which DNA receives its name. Joined to each deoxyribose is one of four possible bases: adenine (A),
cytosine (C), guanine (G), and thymine (T).
All four bases are planar but differ significantly in other respects. Thus, the monomers of DNA consist of a sugarphosphate
unit, with one of four bases attached to the sugar. These bases can be arranged in any order along a strand of
DNA. The order of these bases is what is displayed in the sequence that begins this chapter. For example, the first base in
the sequence shown is G (guanine), the second is A (adenine), and so on. The sequence of bases along a DNA strand
constitutes the genetic information the instructions for assembling proteins, which themselves orchestrate the
synthesis of a host of other biomolecules that form cells and ultimately organisms.
