Also known as ribonucleic acid, is a complex molecule that plays a major role in all living cells. RNA molecules help produce substances called proteins. Proteins are chains of smaller organic molecules known as amino acids. The body uses proteins to build cells and to carry out the cells' work.

RNA is similar in structure to DNA (deoxyribonucleic acid), another important molecule found in cells. Like DNA, all RNA molecules contain hundreds of smaller chemical units called nucleotides. These nucleotides are bonded together chemically to form thin, chainlike molecules called polynucleotides. Unlike DNA, each RNA molecule consists of a single polynucleotide chain. A DNA molecule has two chains. In addition, RNA occurs throughout the cell, while DNA is found mainly in the cell's nucleus.