To build their circuits, the researchers used pieces of DNA to make so-called logic gates—devices that produce on-off output signals in response to on-off input signals. Logic gates are the building blocks of the digital logic circuits that allow a computer to perform the right actions at the right time. In a conventional computer, logic gates are made with electronic transistors, which are wired together to form circuits on a silicon chip. Biochemical circuits, however, consist of molecules floating in a test tube of salt water. Instead of depending on electrons flowing in and out of transistors, DNA-based logic gates receive and produce molecules as signals. The molecular signals travel from one specific gate to another, connecting the circuit as if they were wires.