Understanding Lipids

Lipids are organic compounds that are essential for the growth of cells. Lipids are hydrophilic, meaning they cannot be combined with water, but are easily combined with carbohydrates and proteins. Lipids are more commonly thought of as fats, however, in reality, lipids include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and other substances. In humans, there are five main types of lipids; fatty acids, triglycerides, phospholipids, eicosanoids and steroids.

Fatty Acids
Fatty acids are produced by the breakdown of fats and are considered to be “good fats.” Fatty acids are organic, meaning they contain both carbon and hydrogen within their molecular structure. Fatty acids play a key role in the transportation of oxygen, as well as aiding the growth and development of cells. Some fatty acids are referred to as “essential fatty acids,” because they are critical in the human diet, but cannot be synthesized by the human body.

There are two types of fatty acid; saturated fats and unsaturated fats. Saturated fats carry the highest amount of hydrogen possible, creating four covalent bonds, making them “saturated” with hydrogen. Unsaturated fats, do not carry the maximum amount of hydrogen, and may share multiple bonds over pairs of atoms.

Triglycerides
Triglycerides consist of three fatty acids bonded covalently with a three-carbon alcohol known as glycerol. The bond between the fatty acids and the three-carbon alcohol is created by dehydration synthesis, or a chemical reaction that involves the removal of water. Triglycerides are often referred to as “neutral fats” and can be broken down by hydrolysis, a chemical reaction that involves the addition of water.

Phospholipids
Phospholipids are similar to triglycerides, with one key difference. Instead of three fatty acids bonded the the three-carbon alcohol, one of these fatty acids is replaced by a phosphate group composed of phosphorous, oxygen and hydrogen. Phospholipids are therefore made up of one phosphate group, two fatty acids, and a three-carbon alcohol, glycerol. One unique function of phospholipids is that the phosphate group within the phospholipid attracts water, while the rest of the phospholipid repels water. This type of substance is said to be ambiphilic, meaning it both absorbs and repels water.

Eicosanoids
Eicosanoids are compounds derived from arachidonic acid. Eicosanoids act as hormone messengers between cells. One of the most versatile eicosanoids includes prostoglandins, a substance made up of five carbons and is produced by almost all tissues within the body. Prostoglandins play a role blood clotting, labor contraction and dilation and constriction of blood vessels.

Steroids
Cholesterol is one of the most commonly known steroids found in the human body. Cholesterol has the ability to produce other steroids, such as cortisol, progesterone, estrogen and testosterone. Cholesterol is only produced by animals, and is not found in plants or plant products. Cholesterol is often seen as bad, however, cholesterol is a naturally occurring product in the body and plays a key role in the healthy functioning of the nervous system and the growth and development of cells. Excess levels of cholesterol can be bad, however, cholesterol is essential to the human body.

References:
Saladin. “Major Themes of Anatomy and Physiology.” Anatomy & Physiology: The Unity of Form & Function. 4th ed. New York: Mcgraw Hill, 2007. 57, 58 Print.

What Are Lipids?

What Are Lipids Used For in the Body?

What Are Lipids?

What Are Fatty Acids?

What Are Phospholipids?

What Are Eicosanoids?

Cholesterol and Steroids