Lipid differences

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... 

Carnivores rely on a protein-rich diet and produce new biomass primarily from dietary amino acids, although the enzymes required for de novo amino acid synthesis are present (Garmes et al., 1998). Bone collagen, muscle (meat) and apatite were analyzed for a set of modern southern African herbivores and carnivores (Lee-Thorp et al., 1989). The isotopic analyses showed i C enrichment in bone collagen, apatite and muscle, and depletion in lipids. Difference in values between herbivores and carnivores indicates a trophic effect, which for carbon in bone collagen is 2.5-3%o (Fig. 2). 

Figure 2 Examples of cationic lipids, differing in the head group structure (mono/ poly cationic) and the nonpolar lipid anchor (Chol/hydrocarbon chains). Abbreviations DOTAP, A-[l-(2,3-dioleoyloxy)propyl]-A,A,7V-trimethyl-ammoniumchloride DOTMA, A-[l -(2,3-dioleyloxy)propyl]-A A, A-trimethylammoniumchloride DC-Chol, 3 P"[A-(A, A -dimethylaminoethyl)carbamoyl]-cholesterol DOGS, A, A-dioctodecyl-amidoglycylspermin DORI, A-(l, 2-dioleoyloxypropyl)-A,A-dimethyl-A-hydroxyethyl-ammoniumbromide SpdC, spermidin-cholesterol.

Operational Definition of Lipids How is the definition of lipid different from the types of definitions used for other biomolecules that we have considered, such as amino acids, nucleic acids, and proteins ... 

The effect of double bonds on both transfection and phase behavior is well illustrated by the pair C18 1/C10-EPC and C18 0/C10-EPC. These two lipids differ by one double bond only. However, the unsaturated lipid is over ten times more efficient as transfection agent than the saturated one [112]. The superior efficiency of C18 1/C10-EPC relative to C18 0/C10-EPC is also implied by the phases that evolve in membrane lipid formulations upon mixing with these two cationic lipids. A biomembrane-mimicking lipid formulation DOPC/DOPE/DOPS/Chol 45 20 20 15 remained lamellar in mixtures with C18 0/C10-EPC in contrast, the more efficient C18 1/C10-EPC induced a lamellar-nonlamellar phase conversion in this mixture, which was taking place at physiological temperature (Fig. 27). 

A-2. Both waxes and fats are lipids that contain the ester functional group. In what way do the structures of these lipids differ ... 

It is worth noting that differences among membranes, such as the presence of different lipids, the amount of surface lipid, differences in size and shape of proteins, or physical features of bonding, may cause differences in permeability among membranes. These biochemical and biophysical differences are thought to be responsible for permeability differences in skin from different anatomical regions of the body. 

It should always be borne in mind that published figures for the ecological efficiency of food assimilated for production are averages from studies made over many years. The picture may be very different in years of shortage or plenty, when efficiency, especially as estimated in the period of growth and accumulation of lipid, differs a great deal from the average. 

Concepts of metabolic processes may be distorted if they are based solely on energy. We have already shown that protein production and the accumulation of lipids differ between the three races of European anchovy, but the energy equivalents of the body weights alter identically in all three (Shulman and Urdenko, 1989), even though the metabolic patterns differ. No fish farmer will consider only the caloric content of the feed, but will concentrate on a proper balance of constituents. Only considerations of both matter and energy will give a true understanding of all the processes involved. 

Kittayapong, P., Clark, J.M., Edman, J.D., Potter, T.L., Lavine, B.K., Marion, J.R. and Brooks, M. (1990). Cuticular lipid differences between the malaria vector and nonvector forms of the Anopheles maculatus complex. Med.Vet. Entomol., A, 405 113. 

Polymorphism is the ability of a molecule to take more than one crystalline form depending on its arrangement within the crystal lattice. In lipids, differences in hydrocarbon chain packing and variations in the angle of tilt of the hydrocarbon chain packing differentiate polymorphic forms. The crystallization behavior of TAG, including crystallization rate, crystal size, morphology, and total crystallinity, are affected by polymorphism. The molecular structure of the TAG and several external factors like temperature, pressure, rate of crystalhzation, impurities, and shear rate influence polymorphism (5). 

Animal and plant depot lipids consist primarily of triacylglycerols triesters of glycerol and three fatty acids. Lipids differ from species to species with regard to the types and amounts of fatty acids they contain. Table 1 presents the fatty acid... 

It must be stressed that both transdermal flux and Kp are not only chemical dependent but also tightly constrained by the membrane system studied as well as the experimental design of the study used to estimate it (neat compound, vehicle, length of experiment, etc.). The PC that is integral to Kp is the PC between the surface or applied vehicle and the stratum corneum lipids. Different vehicles will thus result in different PCs. Similarly skin from different species may result in different PC due to differences in the stratum corneum lipids and intercellular path lengths. From the computational toxicology perspective, this translates into quantitative models whose parameters are very dependent on experimental variables often not appreciated to be significant contributors to the process. 

The composition of fish striated muscle with respect to water, proteins, and lipids differs widely from one species to another, and within a species seasonal variations may occur. The influence of this factor has been investigated by Van Wyk (1944). In fatty fishes, an important increase in fat content is observed in Spring or in Summer, with a corresponding decrease in water content, while the nitrogen values remain relatively constant. Determinations made on many species by various authors have been compiled by Jacquot and Creac h (1950). Other evaluations have been done more recently on numerous Spanish fishes (De Las Heras and Mendez Isla, 1952) on a few Kolhapur fresh-water fishes (Airan and Joshi, 1952), and on Skipper Cololabis saira) (Tsuchiya et ah, 1953). Some of the figures given by Jacquot and Creac h (1950) are reproduced in Table I, which contains for each species a mean value or sometimes two values corresponding to the limits of variation. Water accounts for three-... 

Lipids tend to survive better than other organic compounds in archaeological contexts and are amenable to sensitive methods of analysis such as gas chromatography/mass spectrometry (GC/MS). Their insolubility in water increases then-chances for survival. Lipids have been recovered from sediments that are millions of years old and have been identified in materials where no cellular structure remains. Lipids are also important because of their specificity. Certain kinds of lipids differ greatly not only between plants and animals, but among the various families and genera of plants and animals. 

This chapter focuses on the use of different methods for isolation of alkylresorcinols. Alkylresorcinols are members of a lipid group called non-isoprenoid phenolic lipids. Different aspects of the extraction by classical methods and supercritical CO2 are discussed. Supercritical CO2 extraction of alkylresorcinols from rye bran is discussed for the first time. As compared to the classical extraction methods, supercritical CO2 gives higher yields and it allows the separation of the crude extrac into long- and short-chain alkylresorcinol homologues. 

The majority of information on the chemical and physical properties of lipids comes from studies on the major phospholipid classes of eubacteria and eukaryotes with only limited information on the lipids from archaebacteria. The biosynthetic pathways and the genetics of lipid metabolism have also been extensively studied in eubacteria (Chapter 3) and eukaryotes (Chapter 8). Clearly, the archaeol lipids confer some advantage with respect to the environment of archaebacteria. Interestingly, the pathways for phospholipid biosynthesis in eubacteria and archaebacteria are very similar even though their lipids differ in chirality of the glycerol backbone. Many of these organisms exist in harsh environments that call for more chemically stable lipid bilayers that are afforded by the above lipids. How the physical properties of the more commonly studied lipids change with environment will be discussed later. 

Based on these observations, the conflicting reports about the state of alamethicin are understandable in terms of different investigators using different lipids, different lipid-peptide ratios, and different preparation procedures. (It is quite possible that some measurements were made before the samples reached equilibrium.)... 

Another important class of phospholipids is that of phosphati-dylethanolamines, which has Tc higher than the corresponding phospaditylcholines due to their different head groups [24]. In general, mixtures of phospholipids melt over a broader temperature range than pure lipids. In cases when mixtures of lipids differ only in two carbon atoms, the mixing phases are ideal [25],... 

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