If double bonds are present in naturally occurring fats and oils, the double bonds are usually cis rather than trans. Unsaturated fatty acid: A long-chain carboxylic acid containing one or more carbon–carbon double bonds.Saturated fatty acid: A long-chain carboxylic acid containing only carbon–carbon single bonds.The naturally occurring fats and oils are triesters formed between glycerol and fatty acids.Chapter Twenty FourĪ few representative lipid structures are shown below. The eicosanoids are carboxylic acids that are a special type of intracellular chemical messenger.Steroids are tetracyclic molecules that act as hormones and contribute to the structure of cell membranes.The previously listed groups of lipids are all esters or amides of fatty acids, the next two groups of lipids are not: the steroids and the eicosanoids. Glycolipids, different amides derived from sphingosine, contain polar carbohydrate groups on cell surfaces the carbohydrate portion is recognized by and connects to intracellular messengers. Sphingomyelins, amides derived from an amino alcohol (sphingosine), also contain charged phosphate diester groups they are essential to the structure of cell membranes and are abundant in nerve cell membranes.Together with other lipids, they help to control the flow of molecules into and out of cells. Glycerophospholipids are triesters of glycerol that contain charged phosphate diester groups and are abundant in cell membranes. They are a major source of biochemical energy. They make up the fats stored in our bodies and most dietary fats and oils. Triacylglycerols are carboxylic acid triesters of glycerol, a three-carbon trialcohol.
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