Antioxidant

Antioxidants are molecules that prevent the oxidation of other molecules. Oxidation is a chemical reaction in which electrons are lost. In living organisms, this process can be harmful and lead to the breakdown of organic molecules. Antioxidant.

One challenge of life on Earth is that the same thing that makes the oxygen is a large electron acceptor, which makes possible chemical reactions such as the cellular respirationalso makes it highly reactive in potentially harmful ways.

Oxygen “loves” to take electrons from other molecules. Our cells use that “hunger” to “feed” electrons to the oxygen molecules we breathe, which drives the process of cellular respiration.

However, if oxygen or unstable oxygen compounds are let loose inside our cells, they will take electrons from molecules that are assumes that they have them just as easily as they will take electrons that our cells are trying to get rid of.

Some cellular processes also produce dangerous oxygen compounds, such as hydrogen peroxide (H ₂ O ₂ ) as side effects of other biological processes. These oxygen compounds are sometimes referred to be scientists as “reactive oxygen species”, or “ROS” for short.

Oxygen is not the only oxidant in the chemical world; any molecule that takes electrons from other molecules is called an “oxidant”. But the term “oxidant” comes from the name of the oxygen atom, because oxygen is the fiercest oxidant commonly found in the natural world.

When molecules inside cells lose an electron to an oxidising compound, it can start a chain reaction; the molecule that lost its electron can now become an oxidiser. It now “wants” another one, and can take it from a “weaker” molecule, oxidising that one in turn.

The image below uses the example of the fluorine taking electrons from two hydrogen atoms, leaving the hydrogen atoms “hungry” and looking to take electrons from another molecule. Fluorine is an even fiercer oxidant than oxygen, but fortunately for us, it is not often found in the natural world!

To protect themselves from oxidising compounds, living cells produce antioxidants whose job it is to work together to prevent oxidative damage to important cellular molecules such as DNA. Some of these work by seeking out and destroying oxidising compounds, while others block or interrupt oxidation reactions or even repair molecules that have been damaged by oxidation.

“Antioxidant” is more commonly used today to refer to some of these compounds, specifically antioxidants that can be ingested in food, which many health gurus claim will improve health and slow the ageing process.

Less commonly, “antioxidant” can refer to compounds used industrially to prevent oxidative damage to food, equipment and other man-made items.

Function of antioxidants

Inside cells, antioxidants act to protect vital molecules, such as DNA, from oxidising molecules that can occur inside cells. They can do this in a number of ways:

• Binding to oxidants. Some antioxidants bind to oxidant molecules, preventing them from interacting with other vulnerable molecules. Some of these can even transport oxidants such as heavy metals out of the body through the bloodstream and kidneys.
• Shielding vulnerable molecules. Some antioxidants attach themselves to the most important molecules, such as DNA, and serve as “buffers”, preventing oxidant molecules from reaching DNA.
• Repair. Some antioxidants actually repair oxidative damage: they can carry a hydrogen atom or an “extra” electron, which can be donated to molecules that have lost theirs due to oxidation reactions.
• Damage control. Some antioxidants also serve as messengers that promote cellular “suicide” via the apoptosis. While this may not seem very “protective”, cells that have been severely damaged by oxidation can become cancerous. In this way, these damage controllers protect the entire organism.

Benefits of antioxidants

There is some controversy over whether eating antioxidants makes people healthier.

It has long been known that people who eat antioxidant-rich diets are healthier than those who do not. However, foods high in antioxidants, such as berries, nuts, vegetables, whole grains and fish, are healthy for the body in many ways.

These foods are low in sugar and saturated fats, which are major contributors to many common and serious diseases. They are high in fibre, vitamins, minerals, protein and unsaturated fats, all of which work to promote health throughout the body and are deficient in most modern diets.

So are the antioxidants in these foods responsible for the good health of those who eat them?

The results so far have clearly shown that taking an antioxidant pill or supplement cannot replace the good health effects of eating a healthy diet high in antioxidants.

Scientists warn of the dangers of people opting for antibiotic supplements instead of healthy diets. People who take vitamin A, C and E supplements alone have not been found to be healthier than those who do not; and one study found that taking large doses of vitamin A may have been more helpful for cancer cells than for healthy cells.

Many scientists agree that more evidence is needed to determine the long-term effects of antioxidants alone. But they also agree that eating low-fat, low-sugar diets high in fibre, protein, vitamins and minerals is better for health than any pill or supplement.

Examples of antioxidants

Glutathione

Glutathione is an antioxidant that can “donate” an electron and a hydrogen atom to oxidised molecules. This allows it to stop oxidants “feeding” their need for an electron, and to repair molecules that have been damaged by oxidation by giving back the electron they lost.

CoQ10 (ubiquinone)

If you recognise the name “ubiquinone”, good job! This antioxidant is also an important component of the mitochondria in the electron transport chainwhich makes cellular respiration possible.

Because ubiquinone is very good at accepting and donating electrons, it is thought to fight oxidation, either by donating electrons to oxidants, thus neutralising them, or by donating electrons to other antioxidants to regenerate them.

Caretenoids (vitamin A)

Caretenoids are yellow and orange pigments found in plants, including vegetables such as carrots and sweet potatoes. Scientists have also genetically engineered a species of orange-coloured “golden rice”, which helps people in nutrient-poor environments to avoid severe caretenoid deficiencies.

Caretenoids are believed to break the “chain reaction” of oxidation by donating electrons to oxidised species. Although the caretenoid itself is oxidised, it is stable in its oxidised form, so it does not damage any other molecules. The oxidation “chain reaction” stops there, rather than moving on to other molecules that might continue to transmit damage.

Like ubiquinone, the caretenoid called vitamin A has more than one purpose in the body. In addition to being an antioxidant, vitamin A plays a vital role in our cone cells, which make night vision possible. Blindness from severe vitamin A deficiency was a motivation behind the scientific development of golden rice.

Vitamin C

Vitamin C can act as an antioxidant in two ways. It can interact directly with reactive oxygen species to neutralise them; or it can donate an electron to regenerate vitamin E, another important antioxidant species.

Like many other antioxidants, vitamin C has more than one purpose in the body. In addition to acting as an antioxidant, it is essential for the formation of collagen, the protein that gives the skin its natural protective properties. skinThe skin, bones and muscles have their elastic strength.

Vitamin C deficiency: called “scurvy” in earlier centuries, when people did not know about vitamins, manifests itself as extreme problems with connective tissues. In this extreme absence of vitamin C, the teeth of a victim’s teeth may even fall out due to the degradation of the collagen that contained them.

Discover more scientific terms in our scientific dictionary.