Cell Membrane Constituents

Various aspects of the cell membrane are discussed throughout this text, and a brief introduction is presented here. The living system s ability to segregate from and protect itself against—and interact with and against—changes in the external environment is accomplished by membranes. In the body, membranes function at the level of 

Composition of Normal Human Red Blood Cell Membranes (Ghosts)  

Component WT% Grams/Ghost(xl0i3) Approximate Number of Molecules/Ghost (x 10 ) % in Outer Half of Bilayer % in Inner Half of Bilayer 

These lipids contain a long unsaturated hydrocartx n chain amino alchohol known assphingosine 1 OH 

A derivative of sphingosine, in which a fatty add is iinked by an amide linkage, isceramide O 

---

In contrast to drugs acting from the outside on cell membrane constituents,... 

Xenon is an odourless, colourless, non-explosive gas present in the atmospheres of both Earth and Mars in concentrations of approximately 0.08 ppm. Its density is approximately three times and its viscosity twice that of nitrous oxide. Like other noble gases, such as helium and argon, its outer electron shell contains the maximum number of electrons (8) making the molecule highly stable chemically. Despite this, its anaesthetic activity indicates that xenon binds to cell proteins and cell membrane constituents. 

From the schematic model of the plasma membrane we have just depicted, it is clear that the two sides, the inner and the outer surfaces, should have different functions as a result of different structures. Moreover, the lipid bilayer may be considered as a hydrophobic barrier preventing diffusion of water-soluble molecules from both sides, thus maintaining a permanent distinction between the inside and outside of a cell. It also allows the membrane to form closed vessels, which appear to be an absolute requirement for maintaining the fixed asymmetric orientations of the cell membrane constituents. 

Cell membranes. Lipids, particularly the phospholipids, glycolipids, and cholesterol, are important cell membrane components throughout the body. Sphingomyelin, cerebrosides, and gangliosides are particularly important cell membrane constituents in the nervous system. 

Phytosterols The relationship between total dietary phytosterol content and the fatty acid composition of the diet decreases with increasing saturated fatty acids, whereas the total dietary phytosterol content increases with increasing PUFA (86). Phytosterols consist of a mixture of cell membrane constituents that include free sterols, esterified steryls (e.g., esterified to phenolics), steryl glycosides, and acylated steryl glycosides (Table 2). 

Activation of lipases generates free fatty acids and lysolecithins. Lysolecithins are adsorbed within one minute by the cell wall [129], causing a reorganization of cell membrane constituents [130], recognizable by a change of the cell membrane shape [131]. Lysolecithines are reported to activate (at least in mammalian tissue) kinases [132]. 

Because of the great importance of glycoconjugates as cell wall constituents of bacteria and as cell membrane constituents of 1 vertebrates (essentially glycosphingolipids and glycoproteins), a few applications to their syntheses will be discussed. 

Miscellaneous Glycophorin (an intrinsic red blood cell membrane constituent), intrinsic factor (essential for absorption of dietary vitamin B 2), clotting factors (e.g., fibrinogen)... 

Surfactants mnst be chosen with dne care, as their strong interfacial activity can elicit adverse reactions in biological systems. Cell membrane constituents (phospholipids, cholesterol, etc.) can be solubilized at supermicellar concentrations, impairing the integrity of membranes. This disruption of the membrane enhances the permeability of drng substances and other snbstances present in the extracellular fluid. At low concentrations such alterations are reversible and membranes recover rapidly, but higher concentrations... 

Figure 3. Possible CM [-containing vesicles are seen (arrow) in C. neqformans ceils. These vesicles, which are recognized by antibodies to CMH, can move across the periplasmic space and deposit cell membrane constituents on the cell wall. Bar represents 0.1 pm.

In addition, a significant fraction of PMN CL may be the consequence of autooxidation of cell membrane constituents by leakage of reactive oxidants to the extracellular mileu. This is suggested by the intensity and similarity of CL from peroxidation of enzymically inactivated (heat killed) PMN and bacteria. The results indicate that MPO, while enhancing CL, is not necessary for its production within cells. CL initiated by oxidation of ASC in the presence of Cu spectrally parallel PMN induced CL. This system, if operational in PMN, may therefore contribute to the intensity of PMN emission. 

The response of blomolecules and cell membranes Is determined by many factors, some of which are the chemical composition and conformation of the molecules, the surface energy, and topography of the top surface layers which are in contact with biological systems, I.e., body fluids and cells [45]. The work illustrated here consisted In designing new polymers with functional properties capable of promoting the attachment of specific cells. The first step consisted in a polymer system which surface inhibits non-specific cell attachment. This strategy is based on the incorporation of cell membrane constituents such as phosphorylcholine (PC) or phospholipid analogues into polymers [46-51]. 

Zwaal, R.A., Roelofsen, B., and Colley, C.M., 1973, Localization of red cell membrane constituents, Biochim. Biophys. Acta, 300 159. 

---