Chapter 2 Structure and Physical Properties of the Lipid Membrane

Abstract

The chapter discusses the information on the structure and the physical properties of the lipid membrane. A lipid bilayer consists of two apposed lipid monolayers with the hydrophilic lipid head groups facing the surrounding fluid spaces on each side of the bilayer and the hydrophobic lipid hydrocarbon chains localized in the bilayer center. Such an arrangement of lipid molecules represents an ideal functional and structural boundary for cells. The ion gradients across membranes, produced by membrane-embedded ion pumps, are critical to cell functions, including the production of ATP, nerve conduction, and muscle contraction. Moreover, the bilayer is a suitable environment for a variety of membrane-bound enzymes and recognition molecules. Biological membranes of eukaryotic cells contain three main types of lipids: phospholipids, glycolipids, and cholesterol. The zwitterionic phospholipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are the most common membrane phospholipids, but the charged lipids phosphatidylglycerol (PG), phosphatidylserine (PS), and phosphatidylinositol (PI) are also present, and the charged phospholipid cardiolipin is a major phospholipid in the inner mitochondrial membrane. Because of the importance of the lipid bilayer as the structural core of biological membranes, there has been sustained effort to understand the structure and physical properties of phospholipid bilayers.