**5.1 Lipids**

Lipids are the most sensitive biomolecules to the effects of free radicals, and the unsaturated bonds of fatty acids and cholesterol in cell membranes react very easily with free radicals to form peroxidation products. The oxidative breakdown of polyunsaturated fatty acids, known as lipid peroxidation and which is highly harmful, proceeds as a self-sustaining chain reaction [17, 46]. Lipid peroxides, which are an important component of cell membranes, form RS- and ROO- radicals with the presence of transition metals such as Fe and Cu. In this way, Fe and Cu salts increase the rate of lipid peroxidation and consequently reduce the fluidity and permeability of the cell membrane and cause the disruption of membrane integrity [6, 17, 47].
