Each nucleotide consists of a nitrogenous base (T, A, C, or G), the
sugar deoxyribose, and a phosphate group.
The 5' end of the polynucleotide is a phosphate, while the 3' end is a
hydroxyl group of the sugar.
The phosphate of one nucleotide forms a covalent bond with the sugar
of the next, providing a "backbone" from which the bases project.