Free Radicals

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton  

Introduction[edit | edit source]

A free radical is atom or group of atoms that has at least one unpaired electron and is therefore unstable and highly reactive (often only occur as transientspecies). In animal tissues, free radicals can damage cells and are believed to accelerate the progression of cancer, cardiovascular disease, and age-related diseases. In the body it is usually an oxygen molecule that has lost an electron and will stabilize itself by stealing an electron from a nearby molecule[1].

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Free radicals are unstable atoms that can damage cells, causing illness and aging.

  • Atoms are surrounded by electrons that orbit the atom in layers called shells. Each shell needs to be filled by a set number of electrons. When a shell is full; electrons begin filling the next shell.
  • If an atom has an outer shell that is not full, it may bond with another atom, using the electrons to complete its outer shell. These types of atoms are known as free radicals[2].

The reactivity of free radicals is what poses a threat to macromolecules such as DNA, RNA, proteins, and fatty acids. Free radicals can cause chain reactions that ultimately damage cells. eg

  • A superoxide molecule may react with a fatty acid and steal one of its electrons. The fatty acid then becomes a free radical that can react with another fatty acid nearby. As this chain reaction continues, the permeability and fluidity of cell membranes changes, proteins in cell membranes experience decreased activity, and receptor proteins undergo changes in structure that either alter or stop their function. If receptor proteins designed to react to insulin levels undergo a structural change it can negatively effect glucose uptake.

Free radical reactions can continue unchecked unless stopped by a defense mechanism[3].

The Body’s Defense[edit | edit source]

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Free radical development is unavoidable, but human bodies have adapted by setting up and maintaining defense mechanisms that reduce their impact. The body’s two major defense systems are free radical detoxifying enzymes and antioxidant chemicals.

  • Free radical detoxifying enzyme systems are responsible for protecting the insides of cells from free radical damage.
  • An antioxidant is any molecule that can block free radicals from stealing electrons; antioxidants act both inside and outside of cells[3].

The Body’s Offensive[edit | edit source]

While our bodies have acquired multiple defenses against free radicals, we also use free radicals to support its functions.

  • The immune system uses the cell-damaging properties of free radicals to kill pathogens. First, immune cells engulf an invader (such as a bacterium), then they expose it to free radicals such as hydrogen peroxide, which destroys its membrane. The invader is thus neutralized.
  • The thyroid gland synthesizes its own hydrogen peroxide, which is required for the production of thyroid hormone.
  • The free radical nitric oxide has been found to help dilate blood vessels and act as a chemical messenger in the brain.[3]

Theory of Aging[edit | edit source]

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The free radical theory of Aging, one of the nine suggested hallmarks of aging, implicates the gradual accumulation of oxidative cellular damage as a fundamental driver of cellular aging. This theory has evolved over time to emphasize the role of free radical induced mitochondrial DNA (mtDNA) mutations and the accumulation of mtDNA deletions. Given the proximity of mtDNA to the electron transport chain, a primary producer of free radicals, it postulates that the mutations would promote mitochondrial dysfunction and concomitantly increase free radical production in a positive feedback loop.[4]

Image: Free Radicals Damage Mitochondria, which according to the mitochondrial free radical theory of ageing, leads to ageing.

Free Radicals, Antioxidants, and Nutrition[edit | edit source]

Free radicals (e.g., superoxide, nitric oxide, and hydroxyl radicals) and other reactive species (e.g., hydrogen peroxide, peroxynitrite, and hypochlorous acid) are produced in the body, primarily as a result of aerobic metabolism, a process which uses oxygen to removing energy from glucose and stores it in a biological molecule called ATP.

Antioxidants (e.g., glutathione, arginine, citrulline, taurine, creatine, selenium, zinc, vitamin E, vitamin C, vitamin A, and tea polyphenols) and antioxidant enzymes (e.g., superoxide dismutase, catalase, glutathione reductase, and glutathione peroxidases) exert synergistic actions in scavenging free radicals.

There has been growing evidence over the past three decades showing that malnutrition (e.g., dietary deficiencies of protein, selenium, and zinc) or excess of certain nutrients (e.g., iron and vitamin C) gives rise to the oxidation of biomolecules and cell injury.

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Increased risk of free radical damage also occurs with eg habits such as smoking, alcohol, and eating processed foods.

A large body of the literature supports the notion that dietary antioxidants are useful radioprotectors and play an important role in preventing many human diseases (e.g., cancer, atherosclerosis, stroke, rheumatoid arthritis, neurodegeneration, and diabetes).[5]

Well-known antioxidants include vitamin C and vitamin E, both of which are found in fruits and vegetables. A diet including sources of antioxidants is necessary for good health (studies have shown that cancer rates are lower in people with diets rich in fruits and vegetables).

The benefits of supplementing diets with additional antioxidants are lacking. In fact, some studies have shown that taking antioxidant supplements can sometimes increase the risk of cancer. Despite these uncertainties about their efficacy, supplemental antioxidants are a boom industry, sold as a health panacea and added to a range of processed foods, including juices, cereals, chocolate bars, and alcoholic beverages.[6]

References[edit | edit source]