Organic molecules contain carbon and hydrogen. Lipids, carbohydrates, proteins and nucleic acids are the four classes of organic compounds which are the basis for all life on planet Earth. Organic compounds are macromolecules, or very large molecules that are composed of smaller molecules. The class of macromolecules called lipids are chemically dissimilar. What the different types lipids have in common is that they are all insoluble in water, but can be dissolved in organic solvents such as carbon tetrachloride, alcohols, chloroform, ethers and benzene.
Waxes
The four classes of lipids are waxes, fats/oils, phospholipids and steroids. Waxes are a type of lipid that is made by the interaction of alcohol and a fatty acid. Waxes characteristically are composed on a long chain of carbon that has an acid group at the end. They are different from fats and oils because of the alcohol that has combined with the fatty acid to make them. Jojoba oil is an example of an unusual wax that is liquid at room temperature. In general, waxes are used for waterproofing.
Fats
Fats and oils are composed of fatty acids and glycerol. Fats differ from oils because oils are liquid and fats are solid. Fats are the class of lipids that are a major source of energy for the human body, providing twice the amount of energy per calorie when compared to carbohydrates. Fats are produced from the fat content of the diet. A healthy diet is less than 30 percent fats and oils, but the average American has a diet that is 25 to 50 percent fat and oils. Fats are used commercially to make soap and cleaning products.
Phospholipids
Phospholipids are a class of lipid that is found in cell membranes. Cell membrane phospholipids play an important roll in cell to cell communication. Lipid synthesis takes place in the endoplasmic reticulum of liver cells. Lipids are transported from one point to another inside the cell. Outside the cell, lipids are transported by proteins such as albumin, serum proteins and lipoprotein particles.
Steroids
Steroids are lipids which are synthesized from cholesterol and form the basis of hormones. Steroids have a backbone of four carbon rings. Sex hormones are examples of steroids that are synthesized from cholesterol.
Estrogen, progesterone and testosterone are made in the ovaries and testicles. Sex hormones mediate the maturation and functioning of reproductive organs and orchestrate the development of male and female secondary sexual characteristics.
Cortisol is called the "stress hormone" because it is released from the adrenal gland in response to stress. Cortisol is active in the regulation of the human metabolism. Fasting, food intake and the waking state stimulate cortisol release. Steroid medications such as prednisone mimic the actions of cortisol. Long term use of steroid medications cause suppression of the body's own production of this important hormone.
