Nucleic Acid

A nucleic acid is a long molecule made up of smaller molecules called nucleotides. Nucleic acids were discovered in 1868, when twenty-four-year-old Swiss physician Friedrich Miescher isolated a new compound from the nuclei of white blood cells. This compound was neither a protein nor lipid nor a carbohydrate; therefore, it was a novel type of biological molecule. Miescher named his discovery "nuclein," because he had isolated it from the nuclei of cells. Today, his discovery is known as deoxyribonucleic acid (DNA).
Along with DNA, the other major type of nucleic acid in cells is ribonucleic acid (RNA). Both are shown in the above image, in single stranded form. DNA at on the top, and differs from RNA by its inclusion of thymine (T, in red), whereas RNA differs from DNA by its inclusion of uracil (U, yellow).

Nucleic acids are macromolecules, which means they are molecules composed of many smaller molecular units. Thes units are called nucleotides, and they are chemically linked to one another in a chain. In DNA, the nucleotides are referred to in shorthand as A, C, T, and G. In RNA, the nucleotides are A, C, U, and G. The order, or sequence, of the nucleotides in DNA allows nucleic acid to encode an organism's genetic blueprint.
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