Nucleotide Properties

Nucleotides consists of a sugar (ribose in RNA and 2'-deoxyribose in DNA), a heterocyclic base, and at least one phosphate group. The heterocyclic base – adenine (A), guanine (G), cytosine (C), and uracil (U) in RNA, and A,G, C, and thymine (T) in DNA – attaches to the 1' carbon of the sugar via what is called a glycosidic bond (see here). The phosphate group attaches to the 5' hydroxyl group of the sugar. These structural features give nucleotides the following properties:

> 1. The phosphate group of a nucleotide acts as a strong acid (pKa 1), and this is why DNA and RNA are called nucleic acids.

> 2. The amine groups of the purine and pyrimidine bases can be protonated.

> 3. The bases can tautomerize; that is, the bases can redistribute positions of hydrogens and double bonds (Figure 4.4).

> 4. Nucleotides absorb light strongly in the near-ultraviolet region of the spectrum. This makes it possible to use spectrophotometry to quantitate DNA and RNA (Figure 4.5).

See also: Nucleoside and Nucleotide Naming, Phosphodiester Bonds, Polynucleotide Structures, Nucleosides