RNA (Ribonucleic Acid) is a complex compound of high molecular weight that functions in cellular protein synthesis and replaces DNA (deoxyribonucleic acid) as a carrier of genetic codes in some viruses. The nitrogenous bases in RNA are adenine (A), guanine (G), cytosine (C), and uracil (U), which replaces thymine in DNA. RNA is often compared to a copy from a reference book, or a template, because it carries the same information as its DNA template but is not used for long-term storage. RNA and DNA are nucleic acids, and, along with lipids, proteins and carbohydrates, constitute the four major macromolecules essential for all known forms of life. Like DNA, RNA is assembled as a chain of nucleotides, but unlike DNA it is more often found in nature as a single-strand folded onto itself, rather than a paired double-strand.
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