Deoxyribonucleic acid (DNA) is the molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses. DNA is a double-helical polymer composed of two complementary strands of nucleotides paired through hydrogen bonds between adenine–thymine and guanine–cytosine. The structure was elucidated by Watson, Crick, Franklin, and Wilkins in 1953. Sequences of DNA encode proteins via the genetic code, transcribed to messenger RNA and translated by ribosomes.