Q&A: Systems biology

How complex are the systems that systems biologists study? That depends. Some people focus on networks at the ‘omics’-scale: whole genomes, proteomes, or metabolomes. These systems can be represented by graphs with thousands of nodes and edges (see Figure 1). Others focus on small subcircuits of the network; say a circuit composed of a few proteins that functions as an amplifier, a switch or a logic gate. Typically, the graphs of these systems possess fewer than a dozen (or so) nodes. Both the large-scale and smallscale approaches have been fruitful.