Phospholipids molecular structure

Fig. (5). Schematic representation of tlic phospholipids molecular structure and site of action of phospholipases.

Cardiolipin or diphosphatidyl glycerol is one of the most ancient membrane phospholipids from phylogenic aspects. It is surprising for such a complex molecule as cardiolipin to have evolved as one of the major membrane lipids in prokaryotics, when steroids such as cholesterol and phytosterols did not. In eukaryotic cells, cardiolipin is exclusively localized within the mitochondria where it is particularly emiched in the outer leaflet of the inner membrane. Even though a molecular structure of cardiolipin has been conserved in entire organisms, its biological significance has escaped attention except in the case of anti-cardiolipin auto-antibodies which are clinically associated with the Wasserman reaction. 

Konishi, M. (2003). Studies on the molecular structure of highly polyunsaturated phospholipids that promotes the induction of colorectal cancer cells induced by cell differentia ter. "A master s thesis submitted to the graduate school of fisheries sciences, Hokkaido University", pp. 1-115. 

RGURE 17-2 Molecular structure of a chylomicron. The surface is a layer of phospholipids, with head groups facing the aqueous phase. Triacylglycerolssequestered in theinterior (yellow) make up more than 80% of the mass. Several apolipoproteins that protrude from the surface (B-48, C-lll, C-ll) act as signals in the uptake and metabolism of chylomicron contents. The diameter of chylomicrons ranges from about 100 to 500 nm. 

The phase behavior of monolayers is determined by the molecular structure of the am-phiphile and the conditions of the subphase. Phospholipids, for example, attract each other because of van der Waals interactions between the alkyl chains. The longer the alkyl chains, the more strongly the phospholipids attract each other. Thus, the LE-LC transition pressure will decrease with increasing chain length (at constant temperature). Double bonds in the alkyl chains increase this phase transition pressure. Charges and oriented dipole moments (see Chapter 6) in the headgroups, lead to a repulsion between the phopholipids and increase the pressure at which the transition occurs. Salts in the subphase, screen this repulsion and decrease the transition pressure. 

Lecithin (phosphatidylcholine) is a phospholipid, which may be isolated from either egg yolk or soybeans. It is commercially available in high purity for medical uses and has been used to enhance the absorption of insulin in vivo [26]. The antibiotic sodium fusidate, a steroid similar in molecular structure to bile salts has also been shown to have permeation enhancing properties for insulin in vitro [41]. 

Infrared microscopic imaging provides the significant advantages of direct spatially resolved concentration and molecular structure information for sample constituents. Raman microscopy (not further discussed in this chapter) possesses the additional benefit of confocal acquisition of this information and a 10-fold increase in spatial resolution at the expense of reduced signal-to-noise ratios compared with IR. The interested reader is urged to check the seminal studies of the Puppels group in Rotterdam,38 0 as well as our own initial efforts in this direction.41 The current section describes the initial applications of IR microspectroscopic imaging to monitor the permeation and tissue distribution of the dermal penetration enhancer, DMSO, in porcine skin as well as to track the extent of permeation of phospholipid vesicles. 

The study of liquid crystals rapidly becomes complex because both the thermotropic and lyotropic types are polymorphic. The lyotropic type exists in at least six phases according to Brown Johnson. Materials of this type generally exhibit a molecular weight in the range of 250-500. Many of these materials are described as lipids, and frequently as phospholipids. On addition of water to a crystal composed of these materials, the molecular structure initially collapses to form a lamellar structure. Further dilution may result in additional structural changes before an isotropic solution is reached. 

A typical biological membrane is a complex structure composed primarily of lipids and proteins. The major structural components of the bilayer are various lipids. In eukaryotes, the most common type of lipids are phosphatidylcholines, whereas in prokaryotes (such as Escherichia coli), the main lipids are typically phosphatidylethanolamines (1). One example of a typical eukaryotic neutral (zwitterionic) phospholipid is palmitoyl-oleoy 1-phosphatidylcholine (POPC). The molecular structure of POPC is compared to those of dimyristoylphosphatidyl-choline (DMPC) and the negatively charged dimyristoylphosphatidylglycerol (DMPG), commonly used in membrane mimetics, in Fig. 1. 

Provide needed molecular structures through dietary essential fatty acids (EFAs) and phospholipids. 

Phospholipid assemblies may exist in many physical states, depending on their molecular structure, temperature, and environment (Marsh, 1991). The bilayer is the major structure of biological membranes, and the investigated model membranes were often in the gel-... 

The molecular structure of the different phases of phospholipid monolayers have been revealed by a number of techniques, in particular X-ray diffraction and IR reflection. With synchroton X-ray diffraction at grazing incidence the molecular packing of the denser phases (LC and S) has been investigated. 

Therraodjmamics of phospholipids depend on their molecular structure the conformation and the geometry of the phospholipids polar head, the orientation of the molecular backbone (glycerol in the case of glycerophospholipids) and the acyl-chaiiis orientation. NMR spectroscopy has been used extensively in order to reveal the lipid orientation in membrane structures [20]. NMR experiments have shown that except for phospatidic acid, in all phospholipid crystal structures a part of the sn-2 fatty acyl chain is parallel to the bilaycr surface. In egg phosphatidylcholines for example the averege size of the sn-2 acyl chain is 18 carbons while the sn- fatty acid is 16 carbons long. The final configuration of the two fatty acyl chains extends to the same depth from the bilayer surface and a thermodynamicaly stable conformation of the acyl lipid chains is formed [21]. 

Schematic models for the expanded structure of bile acid-phosphatidylcholine mixed micelles are shown in Fig. 2B. The original model was proposed by Small in 1967 (S36). In this model the mixed micelle consisted of a phospholipid bilayer disk surrounded on its perimeter by bile acid molecules, which were oriented with their hydrophilic surhices in contact with aqueous solvent and their hydrophobic sur ces interacting with the hydrocarbon chains of the phosphohpid molecules. This model has recently been revised, based on further studies of mixed micelles using quasi-elastic light scattering spectroscopy (M20). In a new model for the molecular structure of bile acid-phospholipid mixed micelles. Mazer et al. (M20) propose a mixed disk, in which bile acids are found not only on the perimeter of phospholipid bilayers, but also incorporated within their interior in high concentrations (Fig. 2B). The size of these mixed micelles was estimated to be as high as 200 to 400 A in radius in some solutions, and disk-shaped particles in this size range were observed by transmission electron microscopy (M20). Micellar aggregates similar in size and structure to those found in model bile solutions have been demonstrated in dog bile (M22).

Fig. 2.14 (a) Molecular structure of a phospholipid, lecithin (n.b. adopted stereochemistry of glyceryl unit), and (b) phospholipid arrangement in cell membranes. 

The lipid membrane is made up of a variety of fat-derived chemicals, the most important of which are the phospholipids (or lecithins) and ceramides. Phosphatidylcholine (13.7) is a typical phospholipid. The molecular structure is based on glycerol, propan-1,2,3-triol. Two of the alcohol functions are esterified with fatty acids, stearic acid in this case, and the third (one of the primary alcohol functions) with phosphoric... 

These results show that a dyslipidemic microenvironment can directly interfere with DC responses to pathogens and skew the development of T cell-mediated immunity. It will be important to specify the molecular structures within these phospholipid oxidation products that are responsible for their effects on DC function. This will eventually allow designing low molecular substances, which mimic their immunomodulatory effects. 

Figure 1. Molecular structure of types of phospholipid in biological membranes...

Fig. 10.3. Molecular structure of soybean major (PC, PE, and PI) and minor (PS and PA) phospholipids.

Phospholipids (PLs) are attractive molecules because they contain both hydrophobic and hydrophilic residues in their molecular structure. This unique structure gives amphiphilic properties that play an important role in biomembrane organization and... 

The lipids are a group of substances defined in terms of their solubility characteristics. They are water-insoluble substances that can be extracted from cells by organic solvents such as benzene. The lipids found in the human body can be divided into four classes according to their molecular structure fats, phospholipids, waxes, and steroids. 

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