The Role of Lipids

Oxidation occurs more readily in fats (lipids) when compared to protein or carbohydrate molecules. The electrons in lipids are held more loosely than those of other molecules and thereby are more easily attacked by free radicals. Free radicals cause lipid peroxidation - which is destruction of free radicals. Every body cell has a membrane that consists of phospholipid bi-layer, and this layer comprises protein that performs specific functions like transport of molecules and enzymes. To function properly the constituents of the membrane should be fluid so that they can move around freely. The presence of polyunsaturated fatty acid side chains, maintains fluidity. But free radical attacks can start lipid peroxidation that causes reduction of antioxidants and damages protein and membrane lipids.

Singlet oxygen and hydroxyl radical are reactive free radicals and contribute directly towards peroxidation. These steal hydrogen atoms off polyunsaturated fatty acid side chains, and those atoms bond with carbon molecules. And so one of the carbon electrons becomes a free radical (left unpaired). Most often these carbon radicals combine with oxygen of the cell membrane and form other highly reactive radicals.

The cell membranes can acquire protection from peroxidation and resulting free radical in 3 ways: lipid repair, lipid replacement and radical scavenging. To accomplish this antioxidants, play a major role. For example, in cell membranes, Vitamin E is the most powerful scavenger and damaged fatty acids can be repaired with the help of glutathione peroxidase that is an enzyme.