All of the atoms are surrounded by the electrons which are orbiting around the atoms in the shells. Each shell should be filled by a specific number of electrons. When the shell is completely filled, the electrons start filling the next shells. If the outer shell of an atom is not completely filled it may bond with the other atoms by using its electrons for completing its outer shell. Such types of atoms are called free radicals. These radicals are not stable and are in continuous efforts to complete their outer shells.
In recent years significant attention has been given to study the chemistry of free radicals. They are the reactive oxygen species which are generated by the various endogenous system in the body on exposure to the different pathological states or physiochemical conditions. For normal and proper physiological functioning of the body, the number of free radicals should be balanced. Free radicals adversely affect the DNA, proteins, lipids and trigger several diseases.
Splitting of the oxygen molecule to the single atoms causes the formation of free radicals as a single atom of oxygen have unpaired electrons and they tend to form molecules by bonding with the other atoms. If this process continues to happen then it leads to the oxidative stress that can damage the cells of the living bodies and causes a wide range of diseases and cause the wrinkles and other aging symptoms. Free radicals are natural by-products of the metabolic processes. Apart from some negative effects, free radicals are important for life as they turn the food and air into the chemical energy that is the basic requirement of life.
Substances that lead to the formation of the free radicals are present in our food, medicine, water and in our surroundings. Air pollutants and pesticides also lead to the formation of free radicals. Once free radicals are formed then a reaction in the form of the chain can occur. If one free radical is formed then it pulls the electron from a molecule due to which the molecule is destabilized and is turned into the free radical. In turn, this molecule takes an electron from another molecule and the other molecule is also destabilized and is turned to the free radical. Eventually, the whole cell can be disrupted and damaged by this process. This chain reaction for the formation of free radicals may cause the broken cell membranes and it can lose its control over the movement of substances in and outside the cell. As a result, the structure of biomolecules is damaged and free radicals may even change the code of DNA.
To counter effect the toxic implications of free radicals, antioxidants are used. They work by donating an electron to the free radical and the reactivity of free radicals is reduced. Antioxidants have the unique property that even after donating the electrons they do not become the free radicals by themselves. The effects of free radicals cannot be combated by single antioxidant.