What's the Analogy of a Cell?

In the cell you have different kinds of proteins that do specific things to each other in very specific ways. It's a really interesting thing for anyone who's ever tried to build something along the way, always encounter problems. So I'm a little bit puzzled about your use of the word circuit. To me a cell feels sort of more like a city with a lot going on in there,. But what do you have in mind when you speak of a circuit? How is it a cell or is it that the control system of the cell is the circuit? Or what's the analog here?