Structure of phospholipids

Box 11.4 Changes in the type of fat in the diet, modification of the structure of phospholipids and hence membrane structure and the activity of membrane proteins... 

The answer is E. Anesthetics are highly lipid-soluble and experiments with isolated membranes indicate that these molecules can dissolve in the hydrophobic center of the membrane bilayer. This causes a measurable increase in the membrane fluidity by disrupting the packed structure of phospholipids tails. This is considered to be the main, direct mechanism by which this class of drugs inhibits neurotransmission (pain sensations) in neurons. Hallucinogens and opiates may also affect membrane fluidity, but their effects occur by indirect mechanisms, resulting from changes in the protein or lipid composition of the membranes. 

Besides differential scanning calorimetry, electron microscopy can also serve for characterizing the mixing behavior of multicomponent vesicular systems. The ripple structure of phospholipids with saturated alkyl chains (also referred to as smectic Bca phase, Fig. 35) is taken to indicate patch formation (immiscibility) in mixed phos-close enough (1-2 nm) lipid molecules are able to diffuse from one membrane to the between the pre- and main-transition of the corresponding phospholipid, electron... 

Choline is an essential metabolie substance for building und maintaining cell structure. Choline is usually described along with B complex vitamins, although it is essentially a structural component of tissue rather than a metabolic catalyst. Choline is a part of the structure of phospholipids and acetylcholine. 

Conformations based on the few available X-ray structures of phospholipids in the crystalline state, generated from energy minimization or from conformational libraries of phospholipid alkyl chains, have been used as starting structures for the simulation. It has been argued that the latter is preferable in order to save time necessary for equilibration when starting from all-trans conformations of the alkyl chains observed in X-ray structures. To build up the configuration of the system, e.g. the lateral positions of the phospholipids, either crystal structure data or programs... 

Mass spectrometry, especially in the form of fast atom bombardment, has become a potent tool in the elucidation of the structure of phospholipids. In this technique, the phospholipid sample in amounts in the range of 15-100 ng (or more), dissolved in chloroform-methanol (1 1, v/v), is mixed with a glycerol or thioglycerol matrix and placed on a sample mount in the spectrometer. A fast atom gun is then aimed, at a 90° angle, at the sample and the resulting ionized particles are directed to a mass analyzer unit. Under these conditions, most of the energy of the beam is limited to the surface of sample matrix. Consequently, the bulk of the sample is unaltered and can be recovered by solvent extraction. In the case of phospholipids, a mass ion, MH+, is produced also, some fragments are useful for structural analysis. A more... 

It has long been proposed that cytochrome c oxidase contains various phospholipids as intrinsic constituents and that two or three cardiolipins are essential for its catalytic activity (Robinson et al., 1980 Robinson, 1982 Sedlak and Robinson, 1999). However, the composition and structures of phospholipids in the enzyme are still matters of controversy. No experimental evidence has been obtained to discount the proposal that all phospholipids suggested are not intrinsic components of the enzyme. Thus, a careful phospholipid analysis of the crystalline enzyme and an X-ray structure determination are indispensable for the determination of the phospholipid composition. 

Numerous techniques have been employed to examine the monolayer structure of phospholipids at the air/water interface including surface tension, fluorescence, neutron and X-ray reflection, and IR and Raman spectroscopy. In contrast, very few techniques are suitable to examine monolayers at the oil/water interface. Surface tension and fluorescence microscopy [46-48] have shed some light on these buried monolayers, but most other surface techniques are hampered because of effects from the bulk liquids. Since VSFS is insensitive to the bulk, it is an excellent technique for probing these monolayers. 

Dorfler HD. Relationships between miscibility behavior and chemical structure of phospholipids in pseudobinary systems. Colloid Polym. Sci. 2000 278 130-136. 

Seehg J. P Nuclear magnetic resonance and the head group structure of phospholipids in membranes. Biochim. Biophys. Acta 1978 515 105-140. 

The reader is referred to Horrocks (61) for more specific discussion on the nomenclature and structure of phospholipids. 

Research to find out more about the structure of phospholipids and the properties that make them ideal for the construction of cell membranes. 

Scheme 9.1 Structures of phospholipids found in membranes. R and may vary in length. R is usually saturated and R is usually unsaturated.

Faller, R., Sum, A., and de Pablo, J.J. Molecular simulation study on the influence of dimethyl-sulfoxide on the structure of phospholipid bilayers, Biophys.., 85, 3636, 2003. 

Domain structures of phospholipid monolayer LB films were investigated by AFM. The domain structures of phospholipids (di-palmitoyl-phosphatidylcholine, DPPC) were studied as LB films. 

Majewski J, Kuhl TL, Gerstenberg MC, Israelachvili JN, Smith GS (1997) Structure of phospholipid monolayers containing Polyethylene glycol) lipids at the air-water interface. J Phys Chem B 101 3122-3129... 

Fig. 7.3. General structure of phospholipids. R, R hydrocarbon chains. Point A is likely composed of structures noted in the box.

Figure 24. Sketch of the principal molecular structures of phospholipids. These molecules are the main components of cell membranes and may form complex supramolecular aggregates in water.

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