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.
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.