Membrane Structure

Biological membrane A very thin sheath of biological material (thickness ~10 nm to 15 nm) which constitutes the envelope of living cells and also of intracellular organelles, separating them from the environment. Membranes are made up from a lipid bilayer into which proteins are embedded. They are highly organized but are nevertheless fluid enough to […]

Membrane Structure

THE MAIN STRUCTURAL element of the biological membrane is the lipid bilayer. Lipid molecules, when brought into contact with water, spontaneously organize themselves into a bilayer leaflet: The polar lipid head-groups remain in the aqueous environment while the fatty acid tails form the inner hydrophobic core. The lipid bilayer is thus a "sandwich"-like structure with […]

INTRODUCTION (Membrane Structure)

Biological membranes segregate cells and organelles, act as barriers for the passive transport of matter, and support a wide range of important metabolic processes, including active transport, energy flow, signal transduction, and motility. The two main components of membranes are lipids and proteins. Depending on the type of membrane, lipids contribute between 20 and 80% […]

MEMBRANE LIPIDS (Membrane Structure)

Naturally occurring lipids can be divided essentially in two groups: (1) phospholipids containing glycerophosphate as the anchor group for fatty acids, and (2) lipids containing backbones other than glycerol. Phospholipids may be further subdivided into nitrogen-containing lipids, such as phosphatidylcholine (PC), -ethanolamine (PE), -serine (PS), and plasmalogens, and nitrogen-lacking lipids, such as phosphatidic acid (PA), […]


The membrane-water interface comprises the lipid head-group proper, with tightly bound hydration water and a more loosely packed extended hydration layer; the glyc-erol backbone; and the ester linkages of the fatty acyl chains. Due to conformational constraints, the carbonyl group of the sn-2 chain is particularly close to the lipid-water interface, while that of the […]


A. Fatty Acyl Chain Order in Saturated Lipid Membranes The hydrocarbon chains of the lipid bilayer are in a liquid-like state as evidenced by X-ray diffraction, electron spin resonance spectroscopy, and differential scanning calorimetry studies. A quantitative characterization of the hydrocarbon chain order in lipid bilayers by means of 2H-NMR became possible by selectively deuterating […]


A large number of phase diagrams for binary mixtures combining cholesterol with different saturated and unsaturated phosphatidylcholines have been established. Cholesterol at different bilayer concentrations can promote or suppress lateral segregation of phospholipids of differing acyl chain length. Addition of 50 mol% cholesterol to selectively deuter-ated DPPC bilayers leads to an elimination of the gel-to-liquid […]


A. Lipid Order Parameter in the Presence of Amphiphilic Molecules The outer lipid membrane surface of eukaryotic cells is generally uncharged. Amphiphilic, water-soluble molecules such as local anesthetics, viral or antibiotic pep-tides, or peptide toxins therefore partition into the bilayer interface because of their hydrophobicity. All these compounds are found to decrease the order of […]

CONCLUDING REMARKS (Membrane Structure)

Solid-state NMR measurements have shown that functional biological membranes are in the liquid crystalline state and that structural features of lipids in the crystalline phase are essentially carried over into the liquid crystalline state. An order parameter profile comparable for the most diverse membranes has been established. The absolute values of order parameters may, however, […]