Human Biochemistry, Volume 1 - Murray R. 1993

Bioenergetics and Metabolism of Carbohydrates and Lipids
Physiologically Important Lipids
Amphipathic Lipids

Membranes, Micelles, Liposomes, and Emulsions

In general, Lipids are insoluble in Water because they consist predominantly of nonpolar (hydrocarbon) groups. However, Fatty acids, Phospholipids, Sphingolipids, Bile salts, and, to a lesser extent, Cholesterol also contain polar groups. Consequently, one part of the molecule is hydrophobic (water-insoluble) while the other is hydrophilic (water-soluble). Such molecules are termed amphipathic (Fig. 15.34). At an oil-water interface, they orient themselves so that their polar groups reside in the aqueous phase and their nonpolar groups in the oily phase. A bilayer formed by such polar lipids is considered the structural foundation of Introduction/36.html">Biological Membranes (see Chapter 42). Upon reaching a certain critical concentration, polar lipids spontaneously form micelles in an aqueous environment. The aggregation of bile salts into micelles, along with The formation of mixed micelles containing fat Hydrolysis products, facilitates the intestinal absorption of lipids. Ultrasonication of amphipathic lipids suspended in water leads to the formation of liposomes. A liposome is a spherically closed lipid bilayer that encapsulates a portion of the aqueous medium internally. Liposomes hold significant clinical promise, particularly when used in combination with tissue-specific Antibodies; they can serve as targeted drug carriers through the Circulatory system to specific Organs. Emulsions, which consist of a suspension of large nonpolar lipid particles in an aqueous medium, are stabilized by emulsifying agents such as polar lipids (e.g., lecithin). These agents form a surface monolayer that separates the nonpolar core from the aqueous phase (Fig. 15.34).

Class="center">Further Reading

Christie W. W. Lipid Analysis. Pergamon Press. 1973.

Frankel E. N. Chemistry of free radical and singlet oxidation of lipids, Prog. Lipid. Res., 1985, 23, 197.

Gunstone F. D., Harwood J. L., Padley F. B. The Lipid Handbook, Chapman and Hall, 1986.

Gurr A. I., James A.T. Lipid Biochemistry: An Introduction. 3rd ed., Wiley, 1980.

Hawthorne J. N., Ansell G.B. (eds) Phospholipids, Elsevier, 1982.

Johnson A. R., Davenport J. B. Biochemistry and Methodology of Lipids, Wiley, 1971.

Sevanian A., Hochstein P. Mechanisms and consequences of Lipid Peroxidation in biological systems, Annu. Rev. Nutr., 1985, 5, 365.

Vance D. E., Vance J. E. (eds) BIOCHEMISTRY OF LIPIDS and Membranes, Benjamin/Cummings, 1985.