At first glance, the subject of biochemical genetics can seem unbelievably complicated. How can a cell's genes possibly contain all the information about its capabilities for metabolism, macromolecular interactions, and responses to stimuli?

It was only when the Watson-Crick structure was proposed for DNA that it was understood how a "simple" molecule could carry information from one generation to the next. Although there are only four subunits in DNA, information is carried by the linear sequence of the subunits of the long DNA chain, just as the sequence of letters defines the information in a word of text.