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Oxygen is essential to life, but in our bodies,
it is a double-edged sword. Just as metal rusts and food rots when
exposed to the air, so our bodies are vulnerable to contact with air.
Oxygen keeps us alive, but too much of it can be damaging.
The oxidation process occurs in the body naturally. Chemically charged
molecules - known as free radicals - are formed either deliberately
by white blood cells to kill invading bacteria and viruses, or as
a leakage of energy when cells burn food molecules.
In excess, free radicals can cause considerable damage to living cells
and tissue in the body, so their production is kept in check by substances
known as antioxidants, which "neutralise" them.
Molecules are made up of atoms bonded
by pairs of electrons. Two electrons are required to keep this
bond stable, for example there is a pair of electrons in each
of the bonds
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the hydrogen atoms to the oxygen in the water molecule |
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Some molecules, however, especially those containing
oxygen, can easily gain only one of these bonding electrons. This
means the molecule has a "free" chemical bond, or unpaired
electron. This molecule - a free radical - will then "steal"
an electron from neighbouring molecules in order to stabilise itself.
This process - known as oxidation - causes the structure of the neighbouring
molecule to change, and it often becomes a free radical itself.
What makes free radicals potentially dangerous in the body is that
they will "steal" from any other molecule they find. If
they steal from a piece of DNA, a genetic mutation may occur, which
in turn could lead to cancer.
Attack by free radicals, collectively known as oxidative stress, can
cause fundamental biological changes in the body - changes which can
lead to the development of degenerative diseases such as arthritis,
cataracts, diabetes, heart disease and immune-related disorders, depending
on which cells are attached. They are also believed to be the basis
of ageing.
As we get older, the effectiveness of our body's own protective systems
diminishes. Not all free radicals are neutralised, and there is a
slow build of damaged molecules. The same way that friction wears
out a machine, so a free radical wears out our bodies, damage which
shows in the form of diseases typically associated with ageing. |
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