Max Animations

Electrically charged atoms and molecules (ions) require special transport protein (ion channels or ion pumps) to allow them to cross biological membranes. The transport of ions by an ion pump is an active process, resulting in the creation of an unequal distribution of ions on either side of membrane. An electrochemical gradients is built up that stores electrical energy like a capacitor.

The metabolic intermediates of these reactions donate electrons to specialized coenzymes, nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), to form the energy-rich reduced conenzymes, NADH and FADH2. These reduced coenzymes can, in turn, each donate a pair of electrons to a specialized set of electron carriers,  collectively called the electron transport chain.