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Introduction

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High-Yield Terms

  • Essential fatty acid: fatty acid required in the diet due to the inability of human cells to synthesize

  • Omega fatty acid: refers to the location of sites of unsaturation relative to the omega end (farthest from the carboxylic acid) of a fatty acid

  • Monounsaturated fatty acid (MUFA): a fatty acid with a single site of unsaturation, oleic acid, an omega-9 MUFA, is the most physiologically significant MUFA

  • Polyunsaturated fatty acid (PUFA): any fatty acid with multiple sites of unsaturation; omega-3 and omega-6 PUFA are the most significant clinically

  • Plasmalogen: any of a group of ether phospholipids

  • Sphingosine: an amino alcohol that serves as the backbone for the sphingolipid class of lipid, which includes the sphingomyelins and the glycosphingolipids

  • Ceramide: sphingosine containing a fatty N-acylation, serves as the backbone for the glycosphingolipids

  • Glycosphingolipid: any ceramide to which a carbohydrate or carbohydrates have been added, constitutes the cerebrosides, globosides, sulfatides, and gangliosides

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High-Yield Concept

The melting point of fatty acids increases as the number of carbon atoms increases. In addition, the introduction of sites of unsaturation results in lower melting points when comparing a saturated and an unsaturated fatty acid of the same number of carbons. Saturated fatty acids of less than 8 carbon atoms are liquid at physiological temperature, whereas those containing more than 10 are solid.

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Major Roles of Biological Lipids

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Biological molecules that are insoluble in aqueous solutions and soluble in organic solvents are classified as lipids. The lipids of physiological importance for humans serve as structural components of biological membranes; provide energy reserves, predominantly in the form of triglycerides, serve as biologically active molecules exerting a wide range of regulatory functions, and the lipophilic bile acids aid in lipid emulsification during digestion of fats. The biologically relevant lipids consist of the fatty acids, triglycerides, phospholipids, sphingolipids, ceramides, cholesterol, bile acids, eicosanoids, omega fatty acid derivatives, and bioactive lipid derivatives, which also include the inflammation-modulating lipid derivatives.

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Fatty Acids

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Fatty acids are long-chain hydrocarbon molecules containing a carboxylic acid moiety at one end. The numbering of carbons in fatty acids begins with the carbon of the carboxylate group. At physiological pH, the carboxyl group is readily ionized, rendering a negative charge onto fatty acids in bodily fluids. Fatty acids play 3 major roles in the body: (1) they serve as components of more complex membrane lipids; (2) they are the major components of stored energy in the form of triglycerides; and (3) they serve as the precursors for the synthesis of the numerous types of bioactive lipids.

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Fatty acids that do not contain carbon–carbon double bonds are termed saturated fatty acids; those that contain double bonds are unsaturated fatty acids. Fatty acids with multiple sites of unsaturation are termed polyunsaturated fatty acids (PUFAs). The numeric designations used for fatty acids come from the number of carbon atoms, ...

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