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© Dirk Biddle
Free radicals are formed in what is known as the respiratory or metabolic burst, where an enhanced uptake of oxygen leads to the production of hydrogen peroxide, superoxide anions and hydroxyl radicals, all of which play a part in bactericidal activity. It has been noted that environmental factors such as pollution, radiation, cigarette smoke and herbicides can also spawn free radicals.
Once created, with an unpaired electron, free radicals are unstable and can react quickly with other compounds, trying to capture the needed electron to gain stability. Generally, free radicals attack the nearest stable molecule, "stealing" its electron. When the "attacked" molecule loses its electron, it becomes a free radical itself, beginning a chain reaction. Once the process is started, it can cascade, finally resulting in the disruption of a living cell.
Normally, the body can handle free radicals, but if antioxidants are unavailable, or if the free-radical production becomes excessive, damage can occur. Free radical damage accumulates with age.
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Metabolic Burst: Response of phagocytes to particles (particularly if opsonised) and to agonists such as formyl peptides and phorbol esters, an enhanced uptake of oxygen leads to the production, by an NADH dependent system, of hydrogen peroxide, superoxide anions and hydroxyl radicals, all of which play a part in bactericidal activity. (OMD)
Hydrogen Peroxide: An unstable compound (H2O2) used especially as an oxidizing and bleaching agent and as an antiseptic. (M+)
Hydrogen peroxide is produced by vertebrate phagocytes and is used in bacterial killing (the myeloperoxidase halide system). (OMD)
Superoxide Anions: A harmful derivative of oxygen capable of oxidative destruction of cell components. (OMD)
Hydroxyl Radicals: Hydroxyl. The univalent radical OH. This radical is characteristic of hydroxides, oxygen acids, alcohols, glycols, phenols, and hemiacetals. (OMD)
Bacteria: One of the two major classes of prokaryotic organism (the other being the Cyanobacteria). Bacteria are small (linear dimensions of around 1 m), non-compartmentalised, with circular DNA and ribosomes of 70S. Protein synthesis differs from that of eukaryotes and many antibacterial antibiotics interfere with protein synthesis, but do not affect the infected host. Recently bacteria have been subdivided into Eubacteria and Archaebacteria, although some would consider the Archaebacteria to be a third kingdom, distinct from both Eubacteria and Eukaryotes. The Eubacteria can be further subdivided on the basis of their staining using Gram stain. Since the difference between gram-positive and gram-negative depends upon a fundamental difference in cell wall structure it is therefore more soundly based than classification on gross morphology alone (into cocci, bacilli, etc.). (OMD) +++ Any of a group (as kingdom Procaryotae or kingdom Monera or the former class Schizomycetes) of prokaryotic unicellular round, spiral, or rod-shaped single-celled microorganisms that are often aggregated into colonies or motile by means of flagella, that live in soil, water, organic matter, or the bodies of plants and animals, and that are autotrophic, saprophytic, or parasitic in nutrition and important because of their biochemical effects and pathogenicity. (M+)