Figure 1.

Russian nesting doll (matryoshka) analogy for recursive modularity in cellular metabolism. (a) The conceptual nesting of modules in a cell such as a cyanobacterium which contains, for example, (b) light harvesting modules, multiple pathways and carboxysomes, which are composed of proteins, which are composed of domains, the basic unit of protein fold and function. (c) Enzyme-centric view of pathways in which enzymes are visualized as nodes and the boundaries of the pathway module are demarcated by the flow of metabolites. Rewiring metabolite flow with the addition of new enzymes and the altering of native connections allows new pathway modules to be constructed. (Online version in colour.)