Acid, nucleic: One of the molecules in the chromosomes of living cells and viruses that plays a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis. The two chief types of nucleic acids are: DNA (deoxyribonucleic acid) which contains the hereditary information in humans and RNA (ribonucleic acid) which delivers the instructions coded in this information to the cell's protein manufacturing sites.

History: In 1869 Friedrich Miescher developed ways of isolating intact nuclei from cells and analyzing their chemical content. From the nuclei he extracted substances rich in phosphorus and nitrogen. They came to be known as "nucleic acids." Miescher predicted that they would someday be considered as important as proteins. The substances turned out to be deoxyribonucleic acid (DNA) which was found by Avery, MacLeod and McCarty in 1944 to be the genetic material. They proved this clearly by using bacterial DNA to change (transform) the genetic material of other bacteria.