Ceil membranes

At this point an interesting observation can be made. Fluorine atoms are put into anesthetics in order to make the molecules more inert. Instead of entering chemical reactions such molecules cmly participate in intermolecular associations in the ceil membrane, a condition for being used as anesthetics. The most potent anesthetics, however, usually contain a last" hydrogen, often referred to as the acidic hydrogen. Chloroform, halothane, methoxyflurane are in this category. Molecules containing this C H bond are, of course, ejq>ected to enter polar interactions. 

The amino acids of a protein control its location in the cell. Some proteins are water soluble, whereas others are bound to the ceil membrane (plasma membrane), the mitochondrial membrane, and the membranes of the endoplasmic reticulum and nucleus. The association of a protein with a membrane is maintained by a stretch of lipophilic amino acids. Insertion of this stretch into the membrane occurs as the protein is synthesized. Water-soluble proteins are formed on ribosomes that "float" free in the cytoplasm. Membrane-bound proteins are formed on ribosomes that associate with the endoplasmic reticulum (ER). As the amino acids are polymerized in the vicinity of the F,R, a stretch of lipophilic acids becomes inserted into the membrane of the FR. This anchoring of the protein is maintained when it is shuttled from its location in the ER to its desired location in the plasma membrane. 

The Na /K -ATPase of the ceil membrane, which constitutes the Na /K pump, is the main site at which cardiac giycosides act. They bind to the K -binding site, thus inhibiting the enzyme, and this inhibition, through a series of interrelated actions, eventually affects cardiac rhythm and the force of contraction is increased. These are the principal beneficial actions. Examples include digoxin, digitoxin and ouabain. See cardiac glycosides. 

Most ceil membranes are electrically polarized, such that the inside is negative [typically —60 millivolts (mV)J- Membrane potential plays a key role in transport, energy conversion, and excitability (Chapter 13). 

Obviously, in order to plan a molecule to meet the above requirements all the taws according to which the different ceil membranes can be penetrated ought to be known, as well as the physical and physicochemical laws regulating the movement and binding of the molecules within the cell, the functioning and interactions of the metabolising enzymes of the cells, and of course, at which part of the cell microstructure the molecule interferes with the physiological processes and in what direct of indirect way. 

Investigations of Merkle et al. (1965), Baur et al. (1969) and Harris and Dodge (1972) showed that the rapid physiological action of these herbicides can be attributed mainly to the destructive effect of peroxy radicals formed from hydrogen peroxide on the lipids of ceil membranes. 

Fig. 10. Structure of the glycosytinositolphosphate structure used by nature to anchor proteins at the C-terminus to ceil membranes.

Cells need a certain amount of eneigy for maintenance. The maintenance enogy is, for instance, needed for maintaining the proton motive force which is, among other purposes, used for maintaining the ion gradients across the ceil membrane. Furdiermore, eneigy is needed for die turnover of proteins and mRNA, for rqiair and for movement (if mobile). 

Bloom M, Evans E, Mouritsen OG (1991) Physical properties of the fluid lipid-bilayer component of ceil membranes a perspective. Quart Rev Biophys 24(3) 293-297... 

Jiu H, Du Y, Wang X et al (2004) Chitosan kill bacteria through ceil membrane damage. Int J Food Microbiol 95 147-155... 

Kim TH, Lim TW, Lee JC (2007) High-temperature fuel ceil membranes based on mechanically stable... 

Jayakody JRP, Chung SH, Durantino L et al (2007) NMR studies of mass transport in high-acid-content fuel ceil membranes based on phosphoric acid and polybenzimidazole. J Electrochem Soc 154 B242-B246... 

Liposomes have also been used as models for the prediction of drug activity ranging from disruption of bilayers by antimicrobials [144] and the ability of anaesthetics to increase the fluidity of nerve ceil membranes [145]. 

---