Phosphoric head groups

Figure 11.9 shows that it is possible to image a phospholipid membrane bilayer structure with the dark lines corresponding to the polar phosphor head groups (Sagalowicz et al. 2003). The membrane thickness can be estimated as shown by the intensity line scan in Figure 11.9. Interpretation of the images needs an expert view since various artifacts such as beam damage and surface contamination can lead to misinterpretations (Won 2004).

Hydrolysis. The first effect of either acid hydrolysis or alkaline hydrolysis (saponification) is the removal of the fatty acids. The saponification value of commercial lecithin is 196. Further decomposition into glycerol, phosphoric acid, and head groups (ie, choline, ethanolamine, etc) may foUow prolonged heating. Lecithin may also be hydrolyzed by enzymes. 

FIGURE 21-23 Head-group attachment. The phospholipid head group is attached to a diacylglycerol by a phosphodiester bond, formed when phosphoric acid condenses with two alcohols, eliminating two molecules of H20. 

Density profile for water, trehalose, and phospholipid headgroups (nitrogen and phosphorous) for a fully hydrated DPPC bilayer. Simulations at 50°C indicate that trehalose concentration is higher near phospholipid head groups than in the bulk (FaUer et al., 2003). The concentration of trehalose in the aqueous phase is 4% by weight. 

MALDI-IMS of Phospholipids Revealed Cell-Selective Production of PC Molecular Species GPLs comprise a large molecular family in which phosphoric acid is esteri-fied to a glycerolipid. They are subdivided into distinct classes (e.g., PCs, phosphatidylethanolamines, and phos-phatidylinositols) based on the structure of the head group linked to the phosphate, attached at the sn-3 posi-... 

Lipids build up the cell membrane. Chemically, lipids are esters between fatty acids and the threefold alcohol glycerine. The latter can form three ester bonds. The third is an ester with phosphoric acid (Figure 11.5). In the membrane, the hydrophobic parts are parallel. The polar head groups are hydrophilic and point outward. 

Nucleoproteins consist of basic proteins in saltlike linkages with nucleic acids (Chapter VIII). Because nucleoproteins are probably present in all cells and vital to growth, there is tremendous biological interest in the histochemical detection of the nucleic acids. Chromosomes, sperm heads, and certain viruses consist largely of nucleoprotein. Two nucleic acid types occur in plant and animal cells deoxyribonucleic acid (DNA), typically present in the nucleus, and ribonucleic acid (RNA), typically found in the cytoplasm and in the nucleolus (see, however. Chapter VIII). Both contain phosphoric acid groups and purine and pyrimidine bases but differ in the pentose moieties. 

The intracellular and plasma membranes have a complex structure. The main components of a membrane are lipids (or phospholipids) and different proteins. Lipids are fatlike substances representing the esters of one di- or trivalent alcohol and two aliphatic fatty acid molecules (with 14 to 24 carbon atoms). In phospholipids, phosphoric acid residues, -0-P0(0 )-O-, are located close to the ester links, -C0-0-. The lipid or phospholipid molecules have the form of a compact polar head (the ester and phosphate groups) and two parallel, long nonpolar tails (the hydrocarbon chains of the fatty acids). The polar head is hydrophihc and readily interacts with water the hydrocarbon tails to the... 

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