- Simple 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.
- Compound Lipids
- 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.
- Glycolipids:
- 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.
- Sterols:
- 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.
- Derived lipids
- 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.
Sample nomenclature for fatty acids:- Name – Carbon Length : Number of Double Bonds
- Butyric acid – 4:0
- Palmitic acid – 16:0
- Oleic acid – 18:1 (9)
- Linoleic acid – 18:2 (9,12)
- Linolenic acid – 18:3 (9,12,15)
- Arachidonic acid – 20:4 (5,8,11,14)
- Eicosapentaenoic acid – 20:5 (5,8,11,14,17)
- Docosahexaenoic acid – 22:6 (4,7,10,13,16,19)
(position of double bond)
- 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.
