Types of Lipids
Unlike other biological macromolecules, lipids are not polymers as they do not contain monomers (recurring subunits)
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However, most types of lipids (excluding steroids) contain at least one fatty acid chain in their structure
Fatty acids can be linked to the hydroxyl group of alcohols via condensation reactions to produce an ester linkage
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Triglycerides are composed of three fatty acid chains linked to a single glycerol molecule
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In phospholipids, one of the fatty acid chains is replaced by a polar phosphate group
Ester Linkages
Main Classes of Lipids
Lipids can be classified in a number of different ways, according to their chemical composition, fatty acids and capacity to form soap
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Three commonly recognised groups of lipids are simple lipids, compound lipids and derived lipids
Simple Lipids
Simple lipids include esters of fatty acids and alcohol (e.g. glycerol)
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Waxes consist of a fatty acid chain linked to a long chain alcohol group and are used to create waterproof surfaces
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Triglycerides consist of three fatty acid chains linked to a glycerol molecule and are used for energy storage and insulation
Compound Lipids
Compound lipids include esters of fatty acids and alcohol linked to an additional group
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Phospholipids consist of a glycerol molecule linked to two fatty acid chains and one phosphate group – they are a principle component of cell membranes
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Glycolipids consist of a carbohydrate linked to an ester of fatty acids and alcohol – they function to facilitate cell-cell interactions
Derived Lipids
Derived lipids are substances produced from the hydrolysis of simple or compound lipids
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They include signalling molecules such as steroids and prostaglandins, as well as cholesterol
Lipid Classes
Wax
Triglyceride
Phospholipid
Steroid