n brain, muscle, and other tissue with little cell division. By the end of ones lifespan, certain parts of the brain consist of as much as 3% abnormal mtDNA (Ricklefs and Finch, 1995, 22). Many characteristics of aging have been proven to develop as a result of spontaneous mutations. However, many other changes associated with aging cannot be adequately explained by this theory. Damage from Free Radicals A free radical is a fragment of a molecule or atom that contains at least one unpaired electron. Because unpaired electrons are unstable, an uneven electrical charge is created and the electrons attract those of other atoms or molecules to become stable and rectify the electrical imbalance. As they gain electrons from other molecules, they modify the other molecules. In this way, free radicals can damage DNA, and it is known that damaged DNA is involved in the aging process. Free radicals can be formed when atoms collide with one another, as in the impact of x-rays or UV radiation from sunlight on living cells. They can start a chain reaction in which atoms or molecules snatch electrons from one another. This process of losing electrons is known as oxidation. Though oxidative damage can be slowed through the help of enzymes and the absorption of free radicals by antioxidants like vitamins E and C, free radicals continue to cause damage, however little, to DNA (Kronhausen et al., 1989, 78). Cross-linking, or large-scale fusion of large cell molecules, is involved in a process responsible for the wrinkling of skin, the loss of flexibility, and rigor mortis. It occurs when little or no antioxidant activity is present to alleviate the rapid stiffening of body tissues (Kronhausen et al., 1989, 74). In older individuals, oxidized proteins in tissues have been found, and when proteins become oxidized, they usually become inactive. Lipids, which constitute a large part of the cell membrane, may also become oxidized, thereby reducing the fluidit...
