  Recent progress has clarified many features of the global architecture of
biological metabolic networks, which have highly organized and optimized
tolerances and tradeoffs (HOT) for functional requirements of flexibility,
efficiency, robustness, and evolvability, with constraints on conservation of
energy, redox, and many small moieties. One consequence of this architecture is
a highly structured modularity that is self-dissimilar and scale-rich, with
extremes in low and high variability, including power laws, in both metabolite
and reaction degree distributions. This paper illustrates these features using
the well-understood stoichiometry of metabolic networks in bacteria, and a
simple model of an abstract metabolism.
