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# How are free radicals formed in the body?

First of all, let's talk about oxidation.

Oxidation happens in inert matter (e.g. think of a rusty car) and also in living things, all the time.

What is oxidation exactly?

Okay, it will get complex from now on, so take your time to read this and absorb the new information!

A freshly-cut apple turns brown (like the apple image in your module), a bicycle fender becomes rusty, and a copper penny turns green. What do all of these events have in common? They are all examples of a process called oxidation.

Oxidation was first defined as the interaction between oxygen molecules and all the different substances they may contact, from metals to living tissue.

But later on, with the discovery of electrons, oxidation came to be more precisely defined as **the loss of at least one electron when two or more substances interact**.

Those substances may or may *not* include oxygen.

When it involves oxygen, the process of oxidation depends on the amount of oxygen present in the air and the nature of the material it touches. That kind of oxidation happens on a molecular level, we only see the large-scale effects as the oxygen causes free radicals on the surface to break away. In the case of fresh fruit, the skin usually provides a barrier against oxidation. This is why most fruits and vegetables arrive in good condition at the grocery store. Once the skin has been broken, however, the individual cells come in direct contact with air and the oxygen molecules start burning them. The result is a form of rust we see as brownish spots or blemishes.

The secret of preventing oxidation caused by *oxygen* is to provide a layer of protection between the exposed material and the air. Just like the skin on fruits!

Now, oxidation and reduction chemistry, with or without the involvement of oxygen, is known as redox chemistry.

Redox chemistry is the study of chemical reactions by which **electrons are moved from one chemical compound to another**. In such a reaction, the reducing agent undergoes a loss of electrons and is oxidised, while the oxidising agent gets more electrons and is reduced. The expression "**Oxidation Is Losing (electrons), Reduction Is Gaining (electrons)**" is often used by chemistry students to differentiate between the two.

With the basics covered, let’s go back to our bodies and free radicals.

Most cellular processes in the body include redox (oxidation) reactions. When you do aerobic exercise, for instance, the conversion of glucose into usable energy needs oxygen (in air) supplied by your lungs and blood to your muscle cells, that’s why we easily become out of breath. This oxidation reaction taking place in your muscle cells is called the oxidation of glucose, which is part of cell respiration.

But cell respiration also happens when we don’t exercise. In fact, the oxidation of glucose takes place constantly in the body to keep our cells alive!

There are trillions of chemical reactions taking place in each of the 37.2 trillion cells in your body each second. So this is just one example. Scientists in the field of molecular biology would learn some (not all) of these at university – it’s a very complex yet fascinating subject and an active field of research and discovery. Scientists know a lot, but not everything!

Cancer scientists are also studying such reactions, on how free radicals damage DNA, causing mutations, preventing self-repair of DNA, interfering with apoptosis (automatic cell death, therefore promoting cell proliferation), causing aberrant methylation, etc. (all of which can lead to cancer), but sadly they are at very initial stages and there’s still a long way to go.

Now, back to our free radicals. When chemical reactions take place in a cell, what happens is that **the conversion of molecules in the body** (e.g. glucose into ATP using oxygen, per our glucose oxidation example above) **creates free radicals**.

How?

Well, for molecules to change their chemical structure, they need to play around with their electrons. So, for example, an electron detaches from molecule A and then reattaches into the same molecule (A) together with other molecule/s to make molecule B (the conversion molecule). That’s a simple way to put it, and in our example of glucose oxidation, the chemical formula of such conversion looks like this:

C6H12O6 + 6 O2 **→** 6 CO2 + 6 H2O

Another example. When the body uses fat for energy, it oxidises fat molecules (burns fat) and that combustion process also detaches electrons from the fat molecules to convert them into usable energy for the cell.

So far, so good. But **when an electron detaches from a molecule and doesn’t reattach instantly, that molecule is now missing an electron and it becomes a free radical**, which can be harmful to the human body, particularly if the free radical does not reattach to the conversion molecule (also called “redox molecule”) or an antioxidant. So these chemically unstable free radicals will start “stealing” electrons from other molecules in the body (including our DNA molecules!), which can cause DNA damage, prevent DNA repair, or lead to DNA mutations, faulty methylation, etc., all of which foment the formation of cancer cells.

That’s why we need to equip our bodies with antioxidants.

The more exposed you are to free radicals (e.g. you exercise excessively and have way too many free radicals from internal cell processes, or you live in a very polluted area, packed with environmental free radicals), the more antioxidants your body will be using to neutralise them. But if your free radical exposure is too high, antioxidants in the body can become easily depleted, and that’s when problems start to occur: **when your free radical exposure surpasses your antioxidant supply**.

More about oxidation [__here__](https://en.wikipedia.org/wiki/Oxidation_state) and redox chemistry [__here__](https://en.wikipedia.org/wiki/Redox).

AUTHOR: Alex Ruani, Research Director