Lipid bilayer compartmentalization

Liposomes are artificial structures composed of phospholipid bilayers exhibiting amphiphilic properties (Chapter 22). In complex liposome morphologies, concentric spheres or sheets of lipid bilayers are usually separated by aqueous regions that are sequestered or compartmentalized... 

Liposomes are artificial structures composed of phospholipid bilayers exhibiting amphiphilic properties (chapter 12). In complex liposome morphologies, concentric spheres or sheets of lipid bilayers are usually separated by aqueous regions that are sequestered or compartmentalized from the surrounding solution. The phospholipid constituents of liposomes consist of hydrophobic lipid tails connected to a head constructed of various glycerylphosphate derivatives. The hydrophobic interaction between the fatty acid tails is the primary driving force for creating liposomal bilayers in aqueous solutions. 

Some, but not all, of the benefits conferred by compartmentalization inside lipid bilayer membranes can be achieved by surfaces. Surfaces allow concentration of metabolites, and, if the surface is a mineral that is not in redox equilibrium with its surroundings, a surface can provide a source of energy. Compartmentalization can also be achieved inside porous minerals. For example, the walls of hydrothermal vents are porous and trap organic material6 and may indeed have provided the first compartmentalization that allowed the emergence of metabolism and macromolecules in a protected environment.7 Also, there are tiny pores in rocks, including tubes in chroysotile, and there are microcracks in quartz, both of which could support diffusion and dispersion by currents. 

Wu M, Holowka D, Craighead HG, Baird B. Visualization of plasma membrane compartmentalization with patterned lipid bilayers. Proc. Natl. Acad. Sci. U.S.A. 2004 101 13798-13803. Marlin SD, Springer TA. Purifled intercellular adhesion molecule-1 (ICAM-1) is a ligand for lymphocyte function-associated antigen 1 (LEA-1). Cell 1987 51 813-819. 

Biological Membrane A biological membrane is a dynamic compartmental barrier composed of a lipid bilayer noncovalently complexed with proteins, glycoproteins, glycolipids, and cholesterol. 

Most biomolecules are amphiphilic, meaning they have both hydrophilic and hydrophobic groups. In an aqueous environment, these molecules self-assemble where the apolar parts of the molecules are grouped together. Some examples of structures formed as a result of this self-assembly are illustrated in Figure 1.2. The lipid bilayer is in fact the backbone of all biological membranes that makes compartmentalization possible in all cells. The assembly of these molecules would not be possible without the presence of water around them. 

An organelle is a compartmentalized subunit with a living cell that carries out a specific function. Organelles are separated from the rest of the cell by a lipid bilayer membrane that allows it to maintain different concentrations of solutes from the rest of the cell. 

Biological membranes are organized structures that consist of phospholipids and proteins. They are responsible for the compartmentation of a wide variety of chemical activities in cells that are indispensable for life [1], Membrane proteins with different chemical properties and functions are associated with a double layer of phospholipids (see Fig. 1). A phospholipid molecule consists of a hydrophilic head, e.g. phosphatidylcholine, and two hydrophobic tails, which are long hydrocarbon chains. It is energetically favorable for phospholipid molecules in water to form a bilayer and hence a spherical micelle structure. The hydrophobic tails occupy the inside of the bilayer while the hydrophilic heads are directed outward and make contact with the surrounding water. Proteins associated with the outer part of a lipid bilayer are called peripheral membrane... 

It is neither feasible nor appropriate in a book like this to give a detailed presentation of biological membranes, which compartmentalize living matter and perform numerous cell functions as well. However, because of the impetus to the study of surfactants that the membrane-mimetic properties of surfactant structures have provided, it would be a mistake to exclude some mention of membranes in this chapter. We have already noted in connection with Figure 7.7 that a monolayer may collapse into a bilayer that leaves the surfactant in a tail-to-tail configuration. This is exactly the arrangement of molecules in the lipid portion of a cell... 

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