The term 'complex lipids' refers to a diverse group of water-insoluble compounds found in biological membranes. They are characterized by the following general properties:
- They are water insoluble, but soluble in nonpolar organic solvents, such as chloroform, ether, or benzene;
- they may be polar or nonpolar triacylglycerols and cholesterol esters are nonpolar, while phospholipids and sphingolipids are polar;
- they may be saponifiable: the ester bonds of glycerophospholipids are saponifiable, while the amide bonds of sphingolipids are not saponifiable.
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| Polar lipids are amphipathic, meaning that they contain both a hydrophobic domain that forms the membrane environment and a hydrophilic domain that interacts with the aqueous environment. Polar lipids are the major components of all biological membranes, and have other, diverse functions in the cell. This chapter discusses the structure, biosynthesis, and function of the two major classes of polar lipids: glycerophospholipids and sphingolipids.
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