![]() In this system, lipids are given a very detailed as well as all-encompassing definition: "hydrophobic or amphipathic small molecules that may originate entirely or in part by carbanion-based condensations of thioesters (fatty acyl, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids and polyketides) and/or by carbocation-based condensations of isoprene units (prenol lipids and sterol lipids)." This complexity has led to the development of a comprehensive classification system for lipids. The simple classification of lipids based on their reactivity towards bases belies the complexity of possible lipid structures as over 1000 different lipids are found in eukaryotic cells. A general diagrams showing the difference in these structures is shown below.įigure: Comparison of lipids with glycerol and sphingosine as backbones In sphingolipids, a fatty acid is attached through an amide link at C2, and a H or esterified phospho-X group is found at C3. Sphingosine, the backbone for sphingolipids, has a long alkyl group connected at C1 and a free amine at C2, as a backbone. Glycerophospholipids have two fatty acids esterified at carbons 1 and 2, and a phospho-X groups esterified at C3. Triacylglycerides have three fatty acids esterified to the three OHs on glycerol. The first two use glycerol as the backbone. The major saponifiable lipids are triacylglycerides, glycerophospholipids, and the sphingolipids. ![]() I will use the lipid and fat synonymously.įigure: Examples saponifiable and nonsaponifiable lipids ![]() Some define fats as lipids that contain fatty acids that are esterified to glycerol. Lipids are often distinguished from another commonly used word, fats. The nonsaponifiable classes include the "fat-soluble" vitamins (A, E) and cholesterol. These fatty acids are released on based catalyzed ester hydrolysis. Saponifiable lipids contain long chain carboxylic (of fatty) acids, that are linked to an alcoholic functional group through an ester linkage. In one categorization, they can be divided into two majors classes, saponifiable and nonsaponifiable lipids, based on their reactivity with strong bases. They can be classified in a variety of ways. Lipids are small biological molecules which are soluble in organic solvents, such as chloroform/methanol, and are sparingly soluble in aqueous solutions.
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