From Tunneling Pathways to Essential Biological Function

Energy capture, storage, and conversion in living systems relies, fundamentally, on the flow of electrons and protons. The transport of electrons through proteins uses cofactors, special chemical groups that sequester electrons as they hop among these sites thorugh otherwise insulating proteins. These cofactors trade electrons with one another via electron tunneling. Electrons thus move across membranes, generating a proton gradient, and leading to the synthesis of energy storing chemical bonds. Electron transfer reactions also participate in essential reaction of biosynthesis, damage repair, and signaling. Electrons flow in biology on time scales from picoseconds to seconds, and the trick for insuring that the electrons get to the right places at the right times is to employ electon tunneling pathways between the charge localizing cofactors. I will descibe the theoretical framework for describing how proteins control these reations with tunneling pathways, and will discuss research frontiers in that have become accessible to theoretical analysis as a consequence of the tunneling pathways framework. Examples will include the repair of DNA damage by the protein photolyase, the micrometer length scale flow of electrons through extracellular bacterial nanoweires that enable respiration in some aerobic bacteria (when deprived of oxygen) through the use of biotic-abiotic charge exchange (i.e., electron transfer to rocks), and electron bifurcation - a reaction that couples electron flow between two-electron donors and single-electron carriers.