General name for the membrane bound pathways that transfer electrons while pumping protons. The two main examples are oxidative phosphorylation and photo phosphorylation which produce and consume oxygen, respectively. Both use ATPase proton engines to generate phosphorylated compounds for the cell. One is breathing, the other is photosynthesis.

Since cells do not contain wires, this transfer of electrons between the charge carriers known as proteins has to be done in an indirect way. It is not altogether clear how the particle tunnels between carriers, but the distance and the resistance of the protein 'bridge' affect efficiency. The proteins contain porphyrin groups with metals that can be oxidised and reduced quite easily, but these metal cores are buried in their organic shells.