Chain reactions in living organisms

[1] Examples of chain reactions in living organisms are lipid peroxidation in cell membranes [2] and propagation of excitation of neurons in epilepsy.

[3] Nonenzymatic peroxidation occurs through the action of reactive oxygen species (ROS), specifically hydroxyl (HO•) and hydroperoxyl (HO•2) radicals, which initiate the oxidation of polyunsaturated fatty acids.

During the initiation phase, fatty acid radicals are generated, which can propagate peroxidation to other molecules.

[4][5] Reinforced lipids that become part of the membrane if consumed with heavy isotope diet also inhibit peroxidation.

[7] Glutamate excitotoxicity is thought to play an important role in the initiation and maintenance of epileptic seizures.

Chain reaction of lipid peroxidation . Clockwise: a polyunsaturated lipid molecule interacts with an external radical and becomes a lipid radical which is further oxidised to a lipid peroxyl radical. The lipid peroxyl radical interacts with another lipid molecule (its neighbour in the membrane) and converts it into a new lipid radical while itself becomes lipid peroxide. This circle continues without additional external radicals present, destroying a large number of lipid molecules in the membrane.