Chapter 58 : Energetics of the Eukaryotic Edge

Abstract:

The most conspicuous feature in the landscape of cell evolution is the tremendous rift that separates eukaryotes from prokaryotes. This is not apparent at the level of ribosomal RNA sequences, or of molecular biology in general, but leaps to the eye of anyone intrigued by form, function, and evolutionary potential. Prokaryotes have been biochemically most inventive, and found access to all the practicable energy sources our planet has to offer. It’s a good rule of thumb that, if a chemical reaction yields sufficient energy to support life, a prokaryote exists that exploits it. But when judged by their morphology and organization, prokaryotes seem to have advanced little beyond their fossil ancestors of 2 to 3 billion years ago. Some, it is true, have attained structural and behavioral complexity beyond the norm: cyanobacteria and planctomycetes with their internal membranes come to mind, and so do myxobacteria with their elaborate fruiting bodies and wolf-pack hunting habit. Still, these pale by comparison with even the plainest of eukaryotic protists, whose cells are typically a thousand times larger and stuffed with functional machinery. It is almost seems as though the prokaryotes made repeated starts up the ladder of complexity, but always fell short. By contrast eukaryotes, despite their meager metabolic repertoire, burst whatever constraints hampered prokaryotes to experiment with the opportunities afforded by greater cell size and more elaborate organization. Just what is it that made the eukaryotic mode of life so much more “evolvable” than the prokaryotic one?