Lipids—Part

Lipids that contain carbon-carbon double bonds are discussed in Section 10.6. 

Lipids are biomolecules whose properties resemble those of alkanes and other hydrocarbons. They are unlike any other class of biomolecules, though, because they are defined by a physical property, not by the presence of a particular functional group. 

More details concerning cholesterol s structure and properties are presented in Section 29.8. 

Cholesterol is a member of the steroid family, a group of lipids having four rings joined together. Because it has just one polar OH group, cholesterol is insoluble in the aqueous medium of the blood. It is synthesized in the liver and transported to other cells bound to water-soluble organic molecules. Elevated cholesterol levels can lead to coronary artery disease. 

Which of the following compounds can be classified as lipids a. CH3(CH2)7CH=CH(CH2)7CXXDH oleic acid 

Driving an automobiie 10,000 miies at 25 miies per gaiion reieases 10,000 lb of CO2 into the atmosphere. 

The increasing level of atmospheric COj is clearly evident on the graph. Two data points are recorded each year. The sawtooth nature of the graph is due to seasonal variation of CO2 level with the seasonal variation in photosynthesis. (Data recorded at Mauna Loa, Hawaii) 

Problem 4.33 Draw the products of each combustion reaction. 

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In some polysaccharides, the reducing terminal is linked, through a phosphoric diester linkage, to O-1 of a 2,3-di-6 -acylglycerol. This structural feature has been demonstrated for some capsular polysaccharides from E. coli and Neisseria species, - but is probably more common than that. Non-covalent linkage between the lipid part and the cell membrane may explain why extracellular polysaccharides often occur as capsules, and the high (apparent) molecular weight observed for these polysaccharides may be due to micelle formation in aqueous solution. 

Schilling M.R., Khanjian H.P., Carson D.M., Fatty acid and glycerol content of lipids. Part II. Effects of ageing and solvent extraction on the composition of oil paints, Techne, 1997, 5, 71 78. 

The other activity associated with transmembrane receptors is phospholipase C. Phosphatidyl inositol is a membrane phospholipid that after phosphorylation on the head group is found in the membrane as a phos-photidylinostitol bis phosphate. Phospholipase C cleaves this into a membrane associated diacylglycerol (the lipid part) and inositol trisphosphate (IP3, the soluble part). Both play a later role in elevating the level of the second messenger, Ca2+. 

Table 1 shows the composition of the lipid part of Lp(a) in relation to the composition of other lipoproteins (G3). 

A third type of interaction is due to hydrophobic effects. These are the result of nonelectrostatic domains interacting. This type of interaction occurs mainly with the highly lipid-soluble drugs in the lipid part within the cytoplasm of the cell. 

In this section, an example will be given in which a (small) library of a new type of cationic lipids was synthesized and screened for TE (63). For synthesis, combinatorial solid phase chemistry was used. All cationic lipids of the example library are structurally based on 3-methylamino-1,2-dihydroxy-propane as the polar, cationic lipid part. As nonpolar lipid part, different hydrocarbon chains are boimd to the amino group of the scaffold and the amino group was further methylated to get constantly cationic-charged lipids. Lipids were synthesized in both configurations and as racemats, and the counterions were varied as well. Table 1 summarizes the structural features of these lipids. 

This technique was also applied to select the lipid part of the PEG-lipid that would most efficiently anchor the PEG-lipid into the liposomes. As observed, PEG-cholesterol induces a better stabilization than the PEG-PE (Fig. 6). 

This text is divided into seven parts part l, An Overview of Biochemical Structures and Reactions That Occur in Living Systems part 2, Protein Structure and Function part 3, Catalysis part 4, Metabolism of Carbohydrates part 5, Metabolism of Lipids part 6, Metabolism of Nitrogen-Containing Compounds and part 7, Storage and Utilization of Genetic Information. 

The lipid part of the membrane is essentially a two-dimensional liquid in which the other materials are immersed and to which the cytoskeleton is anchored. This last statement is not totally correct, as some membrane bound enzymes require the proximity of particular lipids to function properly and are thus closely bound to them. Simple bilayers formed from lipids in which both hydrocarbon chains are fully saturated can have a highly ordered structure, but for this reason tend to be rigid rather than fluid at physiological temperatures. Natural selection has produced membranes which consist of a mixture of different lipids together with other amphiphilic molecules such as cholesterol and some carboxylic acids. Furthermore, in many naturally occurring lipids, one hydrocarbon chain contains a double bond and is thus kinked. Membranes formed from a mixture of such materials can retain a fluid structure. The temperature at which such membranes operate determines a suitable mixture of lipids so that a fluid but stable structure results at this temperature. It will be seen that the lipid part of a membrane must, apart from its two-dimensional character, be disordered to do its job. However, the membrane bound proteins have a degree of order, as will be discussed below. 

Whilst straight-chain fatty acids are the most common, branched-chain acids have been found to occur in mammalian systems, e.g. in wool fat and butter fat. They are also characteristic fatty acid constituents of the lipid part of cell walls in some... 

Ackman, R.G. (1980). Fish lipids, Part 1. In Advances in Fish Science and Technology (J.J. Connell, ed.), pp. 86-103. Fishing News Books, Oxford. 

Bereuter, T. L., Lorbeer, E., Reiter, C., Seidler, H., and Unterdorfer, H. (1996). Postmortem alterations of human lipids—Part I Evaluation of adipocere formation and mummification by desiccation, in Human Mummies A Global Survey of Their Status and the Techniques of Conservation (K. Spindler, Ed.). New York Wien, 265-273. 

Spin labels are usually molecules that contain a nitroxide moiety with an unpaired electron localized on the nitrogen and oxygen atoms. These labels are specifically incorporated in the lipid part of the biological membrane. In this way, the properties of the different regions of the membrane can be studied. ESR measures the transition... 

Fig. 6 Schematic representation of a complex of DNA-cationic lipid, and b DNA and a mixture of cationic lipid and neutral lipid, the lipid-DNA complexes intercalated in multilamellar membranes of cationic lipid and neutral lipid. Part b was reproduced with permission from [39]...

Volume 71. Lipids (Part C) (in preparation) Edited by John M. Lowenstein... 

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