Lipids: From a biological perspective

Lipids are fats. We generally only think about fats in terms of eating them, and how that fat makes our body look. Mostly, we try to avoid fats and see them as a bad thing, however they are completely essential to our survival and here is why.

There are three main classes of lipids: Triglycerides, steroids and phospholipids. Triglycerides are composed of a glycerol molecule and three fatty acids. A fatty acid is simply a long carbon chain with a carboxyl group at one end. It can have no double bonds (it is saturated), one double bond (it is mono-unsaturated) or multiple double bonds (it is poly-unsaturated). The fatty acids join to the glycerol molecule with an esterification reaction. This molecule is a good source of high density energy storage in animals.

The second major class of lipids is the steroids. The structure of steroids are all derivatives from a common structure of four fused carbon rings. The most well known steroid is cholesterol and it helps maintain the correct fluidity of cell membranes. Like the overall label of fats, cholesterol also often carries a negative connotation for humans due to the build up of cholesterol deposits in the arteries and vessels of people with a high cholesterol intake, potentially leading to a stroke or heart disease. The body needs cholesterol for a number of functions, however we do not need to eat foods containing cholesterol as the body can make all the cholesterol it needs.

lipid bilayer.jpg

The final class of lipids I will be discussing is the phospholipids. These molecules are similar to triglycerides: they are composed of a glycerol molecule bonded to two fatty acids and a phosphate group. These molecules form cell membranes. They are able to do this because the fatty acid tails, containing only carbon and hydrogen, are hydrophobic – they do not want to make any contact with water. In contrast, the phosphate group can form polar bonds with water molecules and so this end is hydrophilic. If we think about the human biological environment, between all the cells is an aqueous environment. Within all the cells is also an aqueous environment, so how do phospholipids orientate themselves? By forming a two-layered structure with all the hydrophilic phosphate groups on the outside of the membrane, and the fatty acid tails contained with the intermembrane space between. This formation is known as the lipid bilayer and makes up the membrane of all animal cells.

This is a brief summary of the three main classes of lipids, and I hope it has been an interesting read about how fats play such an important and essential role in our body!




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