Lipids hydrophobic components

The hydrophobic components of many lipids consist of either isoprenoids or fatty acids and their derivatives 34 Isoprenoids have the unit structure of a five-carbon branched chain 34 Brain fatty acids are long-chain carboxylic acids that may contain one or more double bonds 34... 

In an aqueous medium, the hydrophobic interaction plays a very important role. It is the major driving force for hydrophobic molecules to aggregate in an aqueous medium, as seen in the formation of a cell membrane from lipid-based components. The hydrophobic interaction is not, as its name may suggest, an interaction between hydrophobic molecules. This interaction is related to the hydration structure present around hydrophobic molecules. Water molecules form structured hydration layers that are not entropically advantageous. It is believed that hydrophobic substances aggregate to minimize the number water molecules involved in hydration layers. However, the mechanism and nature of the hydrophobic interaction is not that clear. Unusual characteristics, such as incredible interaction distances, have been reported for the hydrophobic interaction, and the fundamentals of hydrophobic interaction are still under debate even today. 

Surfactant Effects on Microbial Membranes and Proteins. Two major factors in the consideration of surfactant toxicity or inhibition of microbial processes are the disruption of cellular membranes b) interaction with lipid structural components and reaction of the surfactant with the enzymes and other proteins essential to the proper functioning of the bacterial cell (61). The basic structural unit of virtually all biological membranes is the phospholipid bilayer (62, 63). Phospholipids are amphiphilic and resemble the simpler nonbiological molecules of commercially available surfactants (i.e., they contain a strongly hydrophilic head group, whereas two hydrocarbon chains constitute their hydrophobic moieties). Phospholipid molecules form micellar double layers. Biological membranes also contain membrane-associated proteins that may be involved in transport mechanisms across cell membranes. 

Membrane lipids are soluble only in organic solvents, such as chloroform or methanol. Only in these are the individual molecules of lipids solvated and dispersed. Membrane lipids are not soluble in water, because of their hydrophobic components. However, their hydrophilic moieties interact with water molecules. The result is a series of complex structures that are spontaneously formed when membrane lipids come into contact with water. These structures are interpreted in terms of lipid phases. 

In 1972 Singer and Nicolson (1) proposed that biological membranes are fluid-mosaic structures. Their model implied that the lipid bilayer acted as a two-dimensional fluid in which protein complexes and other hydrophobic components could freely diffuse, both rotationally and laterally. Evidence for such motions are numerous (2). Despite this it is also quite obvious that not all proteins in membranes are freely diffusing. Indeed the clustering of proteins to specific regions is necessary to form well known features, such as gap junctions, coated pits etc. 

All P.p. are either hydrophobic, or they possess a strongly hydrophobic grouping, e.g. the phytol residue of chlorophyll. A simple model, in which P.p. are associated with the lipid layer of the thylakoid membrane, is however, unsatisfactory. It is necessary to propose a certain degree of ordered structure for P.p., and this is not possible if P.p. are subject to the random mobility of the lipid membrane components, as demanded by the fluid-mosaic model for membrane structure. Binding of a P. p. molecule to a protein would also be an unsatisfactory model, because the various P.p. would then be too widely separated for the efficient transfer of photons or resonance energy. A more feasible model would involve binding of several P. p. molecules to one protein, and there is much evidence for a system of this kind e.g. several chlorophyll-binding proteins have been isolated from... 

Bloom M, Evans E, Mouritsen OG (1991) Physical properties of the fluid lipid-bilayer component of cell membranes a perspective. Quart Rev Biophys 24(3) 293-397 Killian JA, SaleminkI, de Planque MRR, Lindblom G, Koeppe II RE, Greathouse DV(1996) Induction of nonbilayer structures in diacylphosphatidylcholine model membranes by transmembrane a-helical peptides importance of hydrophobic mismatch and proposed role of tryptophans. Biochemistry 35(3) 1037-1045... 

In conclusion, non-esterified arachidonate shares with other natural lipids the ability to activate various membrane ion channels, some of which are listed in Table 3.2. The precise mechanisms through which these modulatory effects are brought about are not known yet, but they may involve a direct interaction of the lipids with a hydrophobic component located either within the channel molecule or in close association with it. 

Another important class of materials which can be successfiilly described by mesoscopic and contimiiim models are amphiphilic systems. Amphiphilic molecules consist of two distinct entities that like different enviromnents. Lipid molecules, for instance, comprise a polar head that likes an aqueous enviromnent and one or two hydrocarbon tails that are strongly hydrophobic. Since the two entities are chemically joined together they cannot separate into macroscopically large phases. If these amphiphiles are added to a binary mixture (say, water and oil) they greatly promote the dispersion of one component into the other. At low amphiphile... 

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