Defining systems biology: through the eyes of a biochemist

What is systems biology, and more importantly what can it do for us? Here is the view of a biochemist who, while working on cellular signal transduction pathways, became increasingly astounded by a highly paradoxical observation. Signal transduction pathways collect numerous types of information in the form of hormones, growth factors or direct cues via contacts with neighbouring cells. These various types of information are transmitted, processed and integrated via the enzymes and their biochemical reactions that constitute the hardware of signalling pathways. In the end there is usually a specific and reproducible biological response that is appropriate to the stimulus and also fitting the higher context of the tissue or organism. This is the Holy Grail that teases us: understanding the biochemical basis of biological decision making. However, not unlike the medieval legend, the Holy Grail increasingly eludes comprehension the closer the brave knight Percival comes in his search of it. Similarly, it seems that the more knowledge we amass about these pathways the less accurately we can actually tell what will happen and what biological message will be made evident. Of course, we now know that these pathways are not linear but networks, and, to complicate matters further, that any given enzyme can be a component of more than one network. This revelation offers little consolation, as then biological responses are likely to be the result of enormous combinatorial complexity that easily surmounts our comprehension.