Classes of lipids

Differences in lipids and their impact on our health

Depending on the class of lipid, structure may vary. Similar classes have a relatively close appearance. For example, nutritional fats are all quite similar, and follow the basic structural pattern illustrated below.

A "free" fatty acid. A free fatty acid is a solitary molecule which remains (by itself) after emulsification and digestion in the intestinal lumen. Fats need to be free or solitary in order to pass through the intestinal wall and into circulation for use by the body.

In the the illustration above, we can see that the carbon tail of the fat or fatty acid, is composed of a carbon chain. The number of carbons in the chain gives the fat its chemical, physical, and hence, nutritional properties. Why is this? Basic chemistry tells us that each carbon is held to the next by a chemical bond, which is illustrated above. This chemical bond stores energy, which holds the carbon atoms together. If this bond is broken, energy is released. And this is exactly what happens when our body uses a fat for energy. As carbons are removed from the chain, valuable energy is released and used in metabolism. This energy also provides heat for keeping us warm. Brown fat in animals provides a fair quantity of heat to keep the animal warm in the winter. As one can imagine, the more carbons there are in the chain, the more energy there is to be released. However, this is not always the case, and different fats may not be so beneficial for us as well. Let's discuss the reasons why.

Examining the illustration above, we can see that there are single bonds between each carbon in the tail. Although in each section of the tail, a 'zig-zag' pattern exists, overall, the tail has a straight appearance. If we were remove one of the single bonds between carbon atoms, and replace it with a double bond the molecule would no longer have an overall straight appearance as illustrated below.

A free fatty acid with introduction of a double bond in its tail. Notice that the conformation is changed by this double bond. The energy from the double bond applies forces in different areas between carbon atoms resulting in a change in shape. This change significantly alters the nutritional properties of a fat.

When a double bond is introduced into a fat in nature, this has several effects on the consumer. Since the fat is "kinked" in shape, it takes up more space. Therefore, if we arranged a mixture of single-bonded and double-bonded fats "side-by-side", the double-bonded fats take up more space. Keep in mind that fats are used for several purposes. Fats can be stored and used for energy, in place of sugars. Therefore, when we are engaged in strenuous physical activity, and use immediate stores of sugars, fats can then be employed. This is why exercise helps to reduce levels of fat. In some parts of the body, tissues may use fats more preferentially than sugars. For example, the myocardium (muscle tissue of the heart) uses fats more readily than sugars. Therefore, we can see that fats are our friends and not merely something unhealthy. Fats are also used for precursors for hormone production. Fat also serves as a "cushion" and hence "shock absorber". Imagine falling on your backside. The more fat you have there, the less of chance of injury. Fats are also vital to each cell. The surrounding membrane of each cell in our body is composed of fats. In fact, there are two layers of fat in this circular membrane enclosing the cell. This is called a double-lipid membrane, or "bilipid-layer". This membrane protects the cell from the external environment, and has protein channels, which strictly regulate what passes in and out of the cell. Therefore, we can see how important fats are in the diet.

In regards to double-bonds in the fat molecule, this has relevance to our well-being. Since the double-bond causes the molecule to "kind" in comparison to a "straight" or linear fat, the bent shape takes more space. This can help in the lipid membrane of the cell. If a cell is occupied by more "kinked" fats, they take up more space. Therefore, less of these fats are present in the cell membrane. The consequence is that the cell now has less fats in its cell membrane and is therefore, lighter in weight. A more lightweight cell travels easier, and is damaged less. These "kinked" fats are called "unsaturated fats", because they are "not" saturated or full of single bonds. Instead, they have one or more double bonds. This is part of why unsaturated fats are beneficial to us.

Dietary lipid metabolism of Triacylglycerols

Dietary lipid metabolism of Phospholipids

Dietary lipid metabolism of Glycolipids

Cholesterol and steroids

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