Any of a class of organic compounds that are fatty acids or their derivatives and are insoluble in water but soluble in organic solvents. They include many natural oils, waxes, and steroids.
Classification of Lipids:
Triglycerides, neutral fats: Found in adipose tissue, butterfat, lard, suet, fish oils, olive oil, corn oil, etc. Esters of three molecules of fatty acids plus one molecule of glycerol; the fatty acid may all be different.
Waxes: beeswax, head oil of sperm whale, cerumen, carnauba oil, and lanolin. Composed of esters of fatty acids with alcohol other than glycerol; of industrial and medicinal importance.
Phospholipids (phosphatides): Found chiefly in animal tissues. Substituted fats, consisting of phosphatidic acid; composed of glycerol, fatty acids, and phosphoric acid bound in ester linkage to a nitrogenous base.
Lecithin: Found in brain, egg yolk, and organ meats. Phosphatidyl choline or serine; phosphatide linked to choline; a lipotropic agent; important in fat metabolism and transport; used as emulsigying agent in the food industry.
Cephalin: Occurs predominantly in nervous tissue. Phosphatidyl ethanolamine; phosphatide linage to serine or ethanolamine; plays a role in blood clotting.
Plasmalogen: Found in brain, heart, and muscle. Phosphatidal ethanolamine or choline; phosphatide containing an aliphatic aldehyde.
Lipositol: Found in brain, heart, kidneys, and plant tissues together with phytic acid. Phosphatidyl inositol; phosphatide linked to inositol; rapid synthesis and degradation in brain; evidence for role in cell transport processes.
Sphingomyelin: Found in nervous tissue, brain, and red blood cells. Sphingosine-containing phosphatide; yields fatty acids, choline, sphingosine, phosphoric acid, and no glycerol; source of phosphoric acid in body tissue.
Cerebroside: myline sheaths of nerves, brain, and other tissues. Yields on hydrolysis of fatty acids, sphingosine, galactose (or glucose), but not fatty acids; includes kerasin and phrenosin.
Ganglioside: brain, nerve tissue, and other selected tissues, notably spleen; contains a ceramide linked to hexose (glucose or galactose), neuraminic acid, sphingosine, and fatty acids.
Sulfolipid: white matter of brain, liver, and testicle; also plant chloroplast. Sulfur-containing glycolipid; sulfate present in ester linkage to galactose.
Proteolipids: brain and nerve tissue. Complexes of protein and lipids having solubility properties of lipids.
Terpenoids and Steroids
Terpenes: Found in essential oils, resin acids, rubber, plant pigments such as caotenese and lycopenes, Vitamin A, and camphor. Large group of compounds made up of repeating isoprene units; Vitamin A of nutritional interest; fat soluble Vitamin E and K, which are also related chemically to terpenes.
Cholesterol: found in egg yolk, dairy products, and animal tissues. A consituent of bile acids and a precursor of Vitamin D.
Ergosterol: found in plant tissues, yeast, and fungi. Converted to Vitamin D2 on irradiation.
7-dehydrocholesterol: found in animal tissues and underneath skin. Converted to D3 on irradiation.
Androgens and estrogens: (Sex hormones) Found in ovaries and testes.
Adrenal corticolsteroids: adrenal cortex, blood.
Fatty acids: occur in plant and animal foods; also exhibit in complex forms with other substances. Obtained from hydrolysis of fats; usually contains an even number of carbon atoms and are straight chain derivatives.
Classification of fatty acids is based on the length of the carbon chain (short, medium, or long); the number of double bonds (unsaturated, mono-, or polyunsaturated); or essentiality in the diet (essential or non-essential). A current designation is based on the position of the endmost double bond, counting from the methyl (CH3) carbon, called the omega end. The most important omega fatty acids are: Omega 6 - linolein and arachidonic acids and Omega 3 - linolenic, eicosapentaenoic, and docosahexaenoic acids.