ROS and Aging
`Aging ' is defined as regular biological degeneration of cells and tissues with time . It occurs normally after sexual maturity , and continues , until death . Aging is a natural , irreversible process , and slows down cell division and replacement of old and worn out cells and tissues  . Genetics is one definite factor that controls human aging but beyond that , we have learnt that nutrition and diet , and environmental factors play a very important role and may promote or delay senescence  . For many years now , scientists and researches have put forward different theories to
support and explain the phenomenon of aging  . The most popular and widely accepted is the `Free-radical Theory of Aging  ' We also come across factors like reactive oxygen species , and antioxidants when we study about this theory  . It proposes that `oxidative damage ' induced by free radicals is the major under lying factor behind aging , meaning , oxidation of cells causes aging , or more crudely put , rusting of cells , causes aging
The nucleus of every atom is surrounded by a cloud of electrons  These electrons exist in pairs , in each orbital , with opposite spins  . If one electron spins clockwise , the other spins anticlockwise . The paired electrons keep the atom fairly stable , that is , in a state of lower energy  . If , for some internal or external reason one electron of a pair is removed , the atom is then called a `free radical  ' It becomes unpaired with respect to the spin of the lone electron , and enters a state of higher energy , which is relatively unstable  . Free radicals are very reactive , and are believed to be one of the major factors behind aging 
Many molecules in the cell are sensitive , and can be destroyed easily by free radicals . This is why it is believed that free radicals are behind a number of diseases like strokes , cardio-vascular problems and diabetes
Free radicals bring about `oxidation ' damage  . Oxidation does not necessary require the involvement of oxygen , as it implies  . It is defined on the basis of loss of electrons  . Free radicals pull an electron from any convenient molecule . The oxygen radicals are the most common free radicals found in biological pathways . Most other free radicals have oxygen as the central atom  . These are called `Reactive Oxygen Species  ' They are formed mostly in the mitochondria of cells . Our bodies are exposed to free oxygen radicals not only through environmental conditions like excessive sunlight and pollution , but these ROS are also generated endogenously  . They are also produced in diabetics . Other free radicals include superoxide , hydroxyl radical protein radical and nitrogen dioxide 
Since chemical cohesive bonds involve multiple atoms sharing electrons to form a molecule , the unwilling loss of electrons destroys chemical bonds . Taken from proteins , electron loss can cause protein cross linking , a key feature of stiffening tissues , disable hormones and enzymes , and damage cell structures . Taken from DNA , genetic defects can occur , which can cause defective compounds to be metabolized...