Genetic memory resides in specific molecules of deoxyribonucleic acid. The DNA alphabet consists of four letters, the bases, A, T, G, and C. The sequence of letters in a nucleic acid message corresponds to a sequence of the 20 amino acid species in protein. Two molecules of DNA interact with one another by hydrogen bonding between bases on opposite chains. As proposed by Watson and Crick,1 adenine pairs with thymine, and guanine with cytosine. Information is retrieved by transcribing the DNA message in the form of ribonucleic acid and then translating the RNA message into protein. Triplets are translated sequentially, from left to right.
The information encoded in a nucleic acid template enables the reading mechanism to select one from many species of molecules, to define the position of the molecule relative to the previous molecule selected, and to define the approximate time of the event relative to previous