The Biology of Lipids : Integrative and Comparative Perspectives

A unifying feature of lipids is relatively low solubility in aqueous media, yet lipids embody an immensely disparate set of molecules. It can be argued that lipids represent some of the most complex biological molecules. Classes of lipids include hydrocarbons, alcohols, fatty acids, waxes, glycerides, phospholipids, and glycolipids. There are also variations on a theme within a single lipid class. Molecular species that make up a lipid class possess differences that are seemingly subtle, but these differences oftentimes have major consequences for physical properties and ultimately for biological function. The complexities of these molecules (including their composite nature, intricate structure, and daunting nomenclature) have intimidated many a biochemistry student and professor! Not surprisingly, functional diversity is another hallmark of lipid compounds. The wide array of chemical and physical properties of different lipids allow these molecules to perform a variety of roles in biological processes. Polar lipids arranged as bilayers establish barriers to free diffusion of water and solutes, provide a microenvironment for membrane-associated proteins, and organize and maintain an interface between discrete metabolic and functional compartments. Surface lipids are integral to water balance in all terrestrial organisms. Lipids serve as metabolic fuels and signalling molecules (hormones, second messengers, and pheromones). Lipids play specialized roles in many organisms as electrical (myelin) or thermal (blubber) insulators. Surfactant lipids are essential components