Free Radicals, Types, Sources and Damaging Reactions
Submitted by Dr. Tamer Fouad, M.D.
Production of free radicals in cells
With the exception of the unusual circumstances such as ionising radiation, ultraviolet light & other forms of high energy exposure, free radicals are produced, in cells, in general by electron transfer reactions, which can be enzymatically mediated or nonenzymatically mediated. The production of free radicals in cells can happen both accidentally or deliberately. An example of deliberate reactions is the superoxide generated by activated phagocytes and in catalytic reactions e.g. Ribonucleotide reductase (Stubbe J, 1990 and Reichard P, Ehrenberg A, 1983). An example of accidental generation of free radicals would be the leakage of superoxide, hydrogen peroxide & other ROS at the interface of the bacterium & the activated phagocyte (Babior BM, 1978). However the major source of free radicals under normal circumstances is the electron leakage that happens from electron transport chains, such as those in the mitochondria & endoplasmic reticulum, to molecular oxygen generating superoxide.
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