الكاربوهيدرات

Structure and Classification of
Lipids
• Lipid: A naturally occurring molecule from a plant or animal
soluble in nonpolar organic solvents.
• Fatty acid: A long-chain carboxylic acid; those in animal fats
and vegetable oils often have 12–22 carbon atoms.
• Waxes are carboxylic acid esters, RCOOR’ ,with long, straight
hydrocarbon chains in both R groups; they are secreted by
sebaceous glands in the skin of animals and perform mostly
external protective functions.
Copyright © 2010 Pearson
Education, Inc. Chapter Twenty Four 2
Triacylglycerols are carboxylic acid triesters of glycerol, a
three-carbon trialcohol. They make up the fats stored in our
bodies and most dietary fats and oils. They are a major source
of biochemical energy. Glycerophospholipids are triesters of glycerol that contain
charged phosphate diester groups and are abundant in cell
membranes. Together with other lipids, they help to control the
flow of molecules into and out of cells.
• 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.
• Glycolipids, different amides derived from sphingosine, contain
polar carbohydrate groups; on cell surfaces the carbohydrate
portion is recognized by and connects to intracellular
messengers.
Copyright © 2010 Pearson
Education, Inc. Chapter Twenty Four 4
• 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.
• Steroids are tetracyclic molecules that act as hormones and
contribute to the structure of cell membranes.
• The eicosanoids are carboxylic acids that are a special type of
intracellular chemical messenger.