By capitalizing on this fundamental attribute of DNA, Liu, 31, is able to program the outcome of chemical reactions. Traditionally, scientists initiate reactions by combining the starting materials in a flask, where the molecules randomly bump into one another. What results is the desired product, plus a host of unwanted products created by unintended side reactions. Scientists must then separate the desired molecules from the mix, an expensive and time-consuming process. Liu's technique gives him a much greater degree of control. Before throwing his raw ingredients together, he attaches each one to a piece of DNA. The ingredients that he wants to react, he attaches to complementary bits of DNA; the ingredients that he wants to keep away from one another, he attaches to nonmatching DNA. When his tweaked ingredients are combined, the desired molecule forms. Liu's technique enables him to run several sequential reactions in a single beaker all at once.