Cholesterol basic properties

The critical properties, that are essential basic data if a cubic equation of state is used, can be evaluated using group contribution methods but the numerical values obtained depend on the method used. In particular, this fact represents a problem for multifunctional components that are generally involved in processing natural products and/or pharmaceuticals. As an example, depending on the prediction method used, a critical temperature ranging from 817.8 to 1254.0 K can be obtained for cholesterol [60]. 

Qeveral recent investigations using various physicochemical methods have provided convincing evidence to support the contention that the basic structure of most biological membranes consists of a phospholipid bilayer (1,2,3, 4). Studies on phospholipid model membranes can therefore be expected to yield relevant information on the role played by phospholipids in determining the characteristic properties of biological membranes (5). One important aspect of this problem concerns the mechanisms of interaction between the phospholipids and other membrane constituents such as cholesterol, proteins, and different inorganic... 

Cholesterol is a basic constituent of cell membranes and is known to affect their properties [10]. Thus experiments with liposomes incorporating varying amounts of cholesterol may simulate the function of cholesterol in cell mem-... 

In order to understand the complex behavior of cellular membranes and their response to external perturbations Uke electric flelds, one has to elucidate the basic mechanical properties of the lipid bilayer. The signiflcant expansion in recent years of the field of membrane raft-hke domain formation [11, 132, 133] imposes the compelling need for understanding the effect of hpid bilayer composition on membrane properties. Cholesterol, a ubiquitous species in eukaryotic membranes, is an important component in raft-hke domains in cells and in vesicles, which mohvates studies aimed at understanding its influence on the mechanical properties and stability of membranes. 

A phospholipid bIlayer can be of almost unlimited size— from micrometers ( xm) to millimeters (mm) in length or width—and can contain tens of millions of phospholipid molecules. Because of their hydrophobic core, bilayers are virtually Impermeable to salts, sugars, and most other small hydrophilic molecules. The phospholipid bilayer is the basic structural unit of nearly all biological membranes thus, although they contain other molecules (e.g., cholesterol, gly-collplds, proteins), biomembranes have a hydrophobic core that separates two aqueous solutions and acts as a permeability barrier. The structural organization of biomembranes and the general properties of membrane proteins are described In Chapter 5. 

A cell cannot divide or enlarge unless it makes sufficient amounts of additional membranes to accommodate the expanded area of its outer surface and internal organelles. Thus the generation of new cell membranes is as fundamentally important to the life of a cell as is protein synthesis or DNA replication. Although the protein components of biomembranes are critical to their biological functions, the basic structural and physical properties of membranes are determined by their lipid components—principally phospholipids, sphingolipids, and sterols such as cholesterol (Table 18-1). Cells must be able to synthesize or import these molecules to form membranes. 

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