The Art of Ecology, Writings of G. Evelyn Hutchinson

tein pathways) to result in a specific output (break down glycogen). Comparing a cell to a computer, as Dennis Bray does in the book Wetware: A Computer in Every Living Cell, yields a fascinating exploration into the complexity of a cell, yet shortchanges the cell and biological systems in general. The central argument of Wetware is that an individual cell contains thousands of enzymes, each performing reiterative, molecular processes. Enzymes act similarly to transistors, in which enzymatic allostery or competitive inhibition alters activity, much like a change in voltage over a transistor. Furthermore, these enzymes, like transistors, can be ordered in pathways, or electronic circuits, to perform logic operations. This design allows cells to sense a variety of environmental stimuli and take action necessary for survival. However, the similarities between the cell and electronics end there. Unlike electronic circuits, there are no wires connecting enzymes in a pathway. Instead, the cell relies on diffusion and compartmentalization in the form of organelles. Additionally, cellular circuitry is noisy due to its analog nature, and the outcome can be difficult to predict, even in the most well-characterized pathways. Bray acknowledges the difficulties in comparing a cell to electronics. Specifically, his metaphor fails to represent the genetic component of a cell, which is vital and adds to the complexity of cellular function. Cells are not simply the sum of their protein components, or “hardware.” The number and type of enzymes available for molecular processes is the result of gene expression, which is also highly influenced by environmental stimuli and enzymatic pathways. Thus, the molecular circuits, or hardware, of a cell is malleable. Using Bray’s metaphor, this is akin to electronic devices adding and removing transistors depending on the environmental conditions. In this respect, no modern computer can compare to even the most basic of cells. Above all, the genetic material provides all necessary instructions to form another cell, thereby allowing cells to replicate, a unique property of life. Although Bray does touch on the idea of genetic circuits, he only examines them in isolation from all other cellular components. Throughout the book, Bray expands the idea of a cellular computer by discussing computation in the context of multicellular organisms, the nervous system, and evolution. He often digresses with biological or electrical examples — the idea for first videogame, PacMan, is one — which do not necessarily appear to be connected to the central thread of the chapter. Nevertheless, these winding arguments make an entertaining read for the scientist and non-scientist alike. Bray does an admirable job explaining complex biological phenomena, such as the lac operon in E. coli or non-coding RNAs, to non-experts while keeping the attention of people already familiar with these ideas. In this way, Wetware is a complex, highly thought-provoking look at how cells are similar to computers. Or, perhaps more correctly, how computers should try to be like living cells.