Lipid biomolecule

We conclude the discussion of the organic molecules in biological systems by turning our attention to lipids, biomolecules that are soluble in organic solvents. Unlike the carbohydrates in Chapter 27 and the amino acids and proteins in Chapter 28, lipids contain many carbon-carbon and carbon-hydrogen bonds and few functional groups. 

The combustion of alkanes, the concentration of atmospheric carbon dioxide, and global warming (Section 4.14B) An introduction to lipids, biomolecules whose properties can be explained by understanding alkane chemistry cholesterol in the cell membrane (Section 4.15)... 

Lipids differ from the other classes of naturally occurring biomolecules (carbohy drates proteins and nucleic acids) in that they are more soluble m nonpolar to weakly polar solvents (diethyl ether hexane dichloromethane) than they are m water They include a variety of structural types a collection of which is introduced m this chapter... 

Biomolecules interact with one another through molecular surfaces that are structurally complementary. How can various proteins interact with molecules as different as simple ions, hydrophobic lipids, polar but uncharged carbohydrates, and even nucleic acids ... 

We ll see later in this chapter and again in Chapter 29 that carbonyl condensation reactions occur frequently in metabolic pathways. In fact, almost all classes of biomolecules—carbohydrates, lipids, proteins, nucleic acids, and many others—are biosynthesized through pathways that involve carbonyl condensation reactions. As with the or-substitution reaction discussed in the previous chapter, the great value of carbonyl condensations is that they are one of the few general methods for forming carbon-carbon bonds, thereby making it possible to build larger molecules from smaller precursors. We ll see how and why these reactions occur in this chapter. 

We ve now covered two of the four major classes of biomolecuies—proteins and carbohydrates—and have two remaining. We ll cover lipids, the largest and most diverse class of biomolecules, in this chapter, looking both at their structure and function and at their metabolism. 

Chapter 27, Biomolecules Lipids—The chapter has been extensively revised, with increased detail on prostaglandins (Section 27.4), terpenoid biosynthesis (Section 27.5), and steroid biosynthesis, (Section 27.7). 

In this chapter we describe the basic principles involved in the controlled production and modification of two-dimensional protein crystals. These are synthesized in nature as the outermost cell surface layer (S-layer) of prokaryotic organisms and have been successfully applied as basic building blocks in a biomolecular construction kit. Most importantly, the constituent subunits of the S-layer lattices have the capability to recrystallize into iso-porous closed monolayers in suspension, at liquid-surface interfaces, on lipid films, on liposomes, and on solid supports (e.g., silicon wafers, metals, and polymers). The self-assembled monomolecular lattices have been utilized for the immobilization of functional biomolecules in an ordered fashion and for their controlled confinement in defined areas of nanometer dimension. Thus, S-layers fulfill key requirements for the development of new supramolecular materials and enable the design of a broad spectrum of nanoscale devices, as required in molecular nanotechnology, nanobiotechnology, and biomimetics [1-3]. 

The artificial lipid bilayer is often prepared via the vesicle-fusion method [8]. In the vesicle fusion process, immersing a solid substrate in a vesicle dispersion solution induces adsorption and rupture of the vesicles on the substrate, which yields a planar and continuous lipid bilayer structure (Figure 13.1) [9]. The Langmuir-Blodgett transfer process is also a useful method [10]. These artificial lipid bilayers can support various biomolecules [11-16]. However, we have to take care because some transmembrane proteins incorporated in these artificial lipid bilayers interact directly with the substrate surface due to a lack of sufficient space between the bilayer and the substrate. This alters the native properties of the proteins and prohibits free diffusion in the lipid bilayer [17[. To avoid this undesirable situation, polymer-supported bilayers [7, 18, 19] or tethered bilayers [20, 21] are used. 

The complex cascades that comprise the inflammatory reaction are designed primarily to limit tissue damage and prevent or inhibit infection. ROMs play a critical role in both these beneficial processes. However, high level fluxes of toxic free radicals are capable of causing damage to diverse biomolecules, including lipids, proteins, DNA and carbohydrates (discussed below). 

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