Electron transport chains in bacteria
NADH is the most important electron donor and the associated electron transport chain is: NADH → Complex I → Q → Complex III → cytochrome c → Complex IV → O2 where Complexes I, III and IV are proton pumps, while Q and cytochrome c are mobile electron carriers. The electron acceptor is molecular oxygen.
Bacteria and Archaea:
the situation is more complicated, because there are several different electron donors and several different electron acceptors. The generalized electron transport chain in bacteria is:
Electrons can enter the chain at 3 levels & correspond to successively smaller Gibbs free energy chnages for the overall redox reaction Donor → Acceptor
Individual bacteria use multiple electron transport chains., often simultaneously. E. coli on glucos uses two different NADH dehydrogenases & quinol oxidases for a total of 4 different electron transport chains operating simultaneously
All electron transport chains create a transmembrane proton gradient via a proton pump. Bacterial electron transport chains could contain three proton pumps, like mitochondria, or could contain only one or two but the least is at least one.