Nucleic Acids, organic compounds found in the chromosomes of living cells and in viruses. The structure of the nucleic acids in a cell determines the structure of the proteins produced in that cell. Since proteins are the "building blocks" of life, nucleic acids can be considered the "blueprints" of life. Nucleic acids were discovered by Friedrich Miescher, a Swiss biochemist, in 1869. He called them "nucleic" because he believed that they occurred only in the nucleus of the cell.

There are two main types of nucleic acids, which differ slightly in their chemical composition. Deoxyribonucleic acid (abbreviated DNA) ordinarily occurs only in the cell nucleus. Ribonucleic acid (abbreviated RNA) is found both in the nucleus and in the cytoplasm (the main part of the cell exclusive of the nucleus). Viruses usually contain only a single molecule of either DNA or RNA.

Genes, the basic units of heredity, consist solely of DNA (or RNA, as in some viruses). The DNA within a cell can be thought of as a master die, or template, from which proteins are built. A type of RNA called messenger RNA, or m-RNA, transmits information from DNA to the ribosomes, structures in the cytoplasm that assemble amino acids into proteins. Transfer RNA, or t-RNA, transports amino acids from the cytoplasm to the ribosomes. Another form of RNA, called r-RNA, is part of the structure of the ribosomes. Other forms of RNA act as enzymes, or catalysts, in protein production. RNA-containing viruses called retroviruses can reverse the usual cellular process and transmit genetic information from RNA to DNA instead of from DNA to RNA.