Lipids derived from fatty acids

Saccharolipid Lipid derived from fatty acids linked in ester or amide linkages directly to sugar molecules. 

The term lipid includes all compounds that release fatty acids on digestion, so that this definition is more extensive than that of fat. Compounds which are insoluble in water, soluble in organic solvents but not derived from fatty acids have been termed non-saponifiable lipids. They include steroids, terpenes and ubiquinone. 

Triacylglycerols and the ether lipids described in the previous section are classified as neutral lipids. Other neutral lipids are alcohols, waxes, aldehydes, and hydrocarbons derived from fatty acids. These sometimes have specific biological functions. For example, fatty aldehydes are important in the bioluminescence of bacteria (Eq. 23-47). 

Phospholipids and sphingolipids are major components of cell membranes. They are amphipathic molecules that is, one portion of the molecule is hydrophilic and associates with H20, and another portion contains the hydrocarbon chains derived from fatty acids, which are hydrophobic and associate with lipids (see Figure 6-4). 

Eicosanoids are the lipid mediators of inflammation that are derived from fatty acids such as arachidonic acid (AA). AA can undergo metabolism through several pathways to generate a wide variety of lipid mediators, such as prostaglandins (by Cox pathway) and leukotrienes (by Lox pathway), which serve as important intra-and intercellular messengers. - ... 

Other lipids, including triacylglycerols, phosphoacylglycerols, and steroids, are derived from fatty acids and metabolites of fatty acids, such as acetoacetyl-GoA. Free fatty acids do not occur in the cell to any great extent they are... 

Consider a cell membrane lipid derived from linoleic acid, which is an unsaturated fatty acid. Hydrogen atom abstraction of an allylic hydrogen by a hydroxyl radical leads to a resonance-stabilized free allylic radical in which the unpaired electron is delocalized over C-9, C-11, and C-13. 

A major portion of the petroleum used today is derived from lipids of plants deposited in past eons. The structures of most compounds isolated from petroleum suggest a derivation from fatty acids. Various chemical changes have occurred, mostly reduction and decarboxylation, so that most petroleum is comprised of a mixture of odd- and even-chain-length hydrocarbons. Some petroleums have a variety of other compounds that appear to be derived from chemical modification of other types of secondary metabolites. 

Eicosanoids are a very broad class of natural lipids that contain 20 carbons, are derived from fatty acids, and include the prostaglandins as well as leukotrienes, thromboxanes, and prostacyclins, all common and important biologically active molecules. 

Terpenes and steroids (Section 8.10) are structurally unrelated to previous classes of lipid in that their structures do not contain or are not derived from fatty acids. They are considered as lipids because of their solubility characteristics. 

Figure 7 Fatty acids form the basis of most complex lipids. The part of the molecule derived from fatty acids is shown in black, and the part derived from other sources is shown in grey. For phospholipids and plasmalogens, R = choline, ethanolamine, inositol, serine, or a similar head group.

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

The heterogeneous class of compounds marked by solubility in so-called lipid solvents (acetone, hydrocarbons, ether, etc.) and relative insolubility in water, has traditionally been called lipids (3). This historical classification, based upon isolation procedures from natural products, is obviously too broad for simple generalizations since it includes triglycerides, fatty acids, phospholipids, sterols, sterol esters, bile acids, waxes, hydrocarbons, fatty ethers and hydrocarbons. For the purposes of this chapter, we will consider lipids to be fatty acids and their derivatives. 

The properties of fatty acids and of lipids derived from them are markedly dependent on chain length and degree of saturation. Unsaturated fatty acids have lower melting points than saturated fatty acids of the same length. For example, the melting point of stearic acid is 69.6°C, whereas that of oleic acid (which contains one cis double bond) is 13.4°C. 

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