Nirenberg, Marshall Warren (1927-...), an American biochemist, explained how genes determine the function of cells. Nirenberg showed that each codon (sequence of three chemical units in genetic material) forms the arrangement for a specific amino acid when proteins are produced. In 1962, he discovered the code for one amino acid. He and others eventually determined the code for the 20 amino acids involved in protein production. See Amino acid;; Cell. Nirenberg won the 1968 Nobel Prize for physiology or medicine.