<P> NADH → Complex I → Q → Complex III → cytochrome c → Complex IV → O where Complexes I, III and IV are proton pumps, while Q and cytochrome c are mobile electron carriers . The electron acceptor is molecular oxygen . </P> <P> In prokaryotes (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: </P> <P> Note that electrons can enter the chain at three levels: at the level of a dehydrogenase, at the level of the quinone pool, or at the level of a mobile cytochrome electron carrier . These levels correspond to successively more positive redox potentials, or to successively decreased potential differences relative to the terminal electron acceptor . In other words, they correspond to successively smaller Gibbs free energy changes for the overall redox reaction Donor → Acceptor . </P> <P> Individual bacteria use multiple electron transport chains, often simultaneously . Bacteria can use a number of different electron donors, a number of different dehydrogenases, a number of different oxidases and reductases, and a number of different electron acceptors . For example, E. coli (when growing aerobically using glucose as an energy source) uses two different NADH dehydrogenases and two different quinol oxidases, for a total of four different electron transport chains operating simultaneously . </P>

What is the final product of the electron transport chain