A
nucleic acid is a
macromolecule composed of chains of monomeric
nucleotides. In
biochemistry these
molecules carry
genetic information or form structures within
cells. The most common nucleic acids are
deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA). Nucleic acids are universal in living things, as they are found in all cells and
viruses. Nucleic acids were first discovered by
Friedrich Miescher.
The term "nucleic acid" is the generic name for a family of biopolymers, named for their role in the cell nucleus. The monomers from which nucleic acids are constructed are called nucleotides.
Each nucleotide consists of three components a nitrogenous heterocyclic base, which is either a purine or a pyrimidine; a pentose sugar; and a phosphate group. Nucleic acid types differ in the structure of the sugar in their nucleotides - DNA contains 2-deoxyriboses while RNA contains ribose (where the only difference is the presence of a hydroxyl group). Also, the nitrogenous bases found in the two nucleic acid types are different adenine, cytosine, and guanine are found in both RNA and DNA, while thymine only occurs in DNA and uracil only occurs in RNA. Other rare nucleic acid bases can occur, for example inosine in strands of mature transfer RNA.
Nucleic acids are usually either single-stranded or double-stranded, though structures with three or more strands can form. A double-stranded nucleic acid consists of two single-stranded nucleic acids held together by hydrogen bonds, such as in the DNA double helix. In contrast, RNA is usually single-stranded, but any given strand may fold back upon itself to form secondary structure as in tRNA and rRNA. Within cells, DNA is usually double-stranded, though some viruses have single-stranded DNA as their genome. Retroviruses have single-stranded RNA as their genome.
