Composition and Role of Phospholipids

A D Postle, University of Southampton, Southampton, UK

© 2005 Elsevier Ltd. All rights reserved.

Phospholipids are amphipathic (amphipathic describes molecules with regions that are both water seeking (hydrophillic) and water repellent (hydrophobic). This is the fundamental physical property that drives the formation of biological membranes) lipids consisting of hydrophobic and hydrophilic regions. This amphipathic nature, which enables phospholipid molecules to assemble into bilayer and hexagonal membrane structures, is critically important for the functional viability of all eukaryote cells. Cellular membranes, composed primarily of phospholipid, separate the intracellular milieu from the extracellular environment and facilitate the formation of specialised intracellular organelles. For many years, phospholipids were considered to be important but relatively inert structural components of the cell. Recently, the central role of membrane phospholipid composition and turnover in the regulation of a wide range of cellular functions has become widely recognized. For instance, all membrane receptor events take place

H3N-CH2CH2SO-

within a phospholipid-rich environment, and it is therefore not surprising that cells have adopted hydrolysis of membrane phospholipids as a major signaling mechanism. Phospholipids have multiple roles, including the following:

1. They provide a structural framework to maintain cellular integrity and to compartmentalize diverse events within the cell.

2. They provide the appropriate physicochemical environment to optimize the activities of membrane-associated receptors, enzymes, and proteins.

3. They act as substrate molecules for a variety of phospholipase enzymes involved in signaling mechanisms.

4. They provide sites for binding of proteins involved in cellular signaling processes.

5. They exert a physicochemical detergent-like action to facilitate the physiological function of a variety of tissues, including the lungs, stomach, and synovial surfaces.

6. They regulate the synthesis and secretion of lipo-proteins from the liver.

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