Transcript OILS
Spencer L. Seager Michael R. Slabaugh www.cengage.com/chemistry/seager Chapter 18: Lipids Jennifer P. Harris IMPORTANT FUNCTIONS OF LIPIDS • • • • Protective wax coatings found on some plants Energy-rich compounds with low densities Storage form of energy for plants and animals Structural components, especially in cellular membrane formation LIPID CLASSIFICATION • Lipids are biological compounds that are soluble only in nonpolar solvents. LIPID CLASSIFICATION (continued) • Saponifiable lipids contain an ester that can undergo basic hydrolysis. • Triglycerides, waxes, phospholipids, and sphingolipids • Simple lipids contain a fatty acid and alcohol. • Triglycerides and waxes • Complex lipids contain a fatty acid, alcohol, and other components. • Phospholipids and sphingolipids • Nonsponifiable lipids do not contain an ester and cannot be hydrolyzed. • Steroids and prostaglandins FATTY ACIDS • Fatty acids: • are the building blocks of many lipids. • are long chain carboxylic acids. • have long nonpolar tails responsible for fatty/oily characteristics. • The carboxyl group is very hydrophilic under conditions of physiological pH (exists as –COO-). FATTY ACIDS (continued) • In water, fatty acids will form spherical clusters called micelles. • Micelles are important for biological functions, like the transport of insoluble lipids in the blood. FATTY ACIDS (continued) • Fatty acids are: • usually straight chains (no branching). • usually from C10 to C20. • usually an even number of carbons. • either saturated (no C=C bonds) or unsaturated (has C=C bonds, usually in the cis configuration). • Examples of saturated, monounsaturated, and polyunsaturated fatty acids containing 18 carbon atoms include: FATTY ACIDS (continued) • Cis C=C causes “kinking” of the carbon chain: FATTY ACIDS (continued) • Fatty acids with C=C bonds cannot pack closely together because of shape. This leads to decreased intermolecular attractions and lower melting points. • Fatty acid melting points decrease as the number of C=C bonds increases. • Most unsaturated fatty acids are liquids at room temperature. FATTY ACIDS (continued) • Essential fatty acids are those needed by the body, but not synthesized within the body in adequate amounts. • For humans, linoleic and linolenic acid are essential, but easily obtainable from plant and fish oils. FATTY ACIDS (continued) • Linoleic (an omega-3 fatty acid) and linolenic (an omega-6 fatty acid) acids: • are used to produce hormonelike substances that regulate a wide range of functions and characteristics, including: • e.g. blood pressure, blood clotting, blood lipid levels, the immune response, and the inflammation response to injury and infection. • can be converted to other omega-3 and omega-6 fatty acids. STRUCTURE OF FATS AND OILS • Fats are: • usually from animal sources. • solids at room temperature. • usually composed to a high degree of saturated fatty acids. • Oils are: • usually from plant and fish sources. • liquids at room temperature. • usually composed of more unsaturated fatty acids than fats. STRUCTURE OF FATS AND OILS (continued) • Fats and oils are triglycerides (triacylglycerols) which are triesters of glycerol. STRUCTURE OF FATS AND OILS (continued) • Fatty acid components in naturally occurring triglyceride molecules are rarely identical. • Natural triglycerides are usually mixtures of different triglyceride molecules. STRUCTURE OF FATS AND OILS (continued) • An example of the esterification process: STRUCTURE OF FATS AND OILS (continued) • Excessive fat in the diet: • is recognized as a risk factor influencing the development of chronic disease. • is a concern because of its role in raising blood cholesterol levels. • High cholesterol is a risk factor in the development of coronary heart disease (leading cause of death in Americans every year). REACTIONS OF FATS AND OILS • Hydrolysis is important for fat and oil digestion. • Enzymes (lipases) can catalyze the hydrolysis process. REACTIONS OF FATS AND OILS (continued) • Saponification is the commercial production of the salts of fatty acids (soaps). REACTIONS OF FATS AND OILS (continued) • Soaps depend on the base used for saponification. • Sodium salts (hard salts) found in cake soap. • Potassium salts (soft soaps) found in shaving creams and liquid soap preparations. • Traditional soap making: • uses animal fat is the source of triglycerides. • uses lye (crude NaOH) or an aqueous extract of wood ashes is the source of the base. • was lost with fall of Roman Empire. • The soapless centuries AD 500-1500 resulted in devastating plagues in an unsanitary western Europe. REACTIONS OF FATS AND OILS (continued) • Hydrogenation decreases the degree of unsaturation and is used to make margarines from oils. • Complete hydrogenation results in a hard and waxy product. • Partial hydrogenation results in a smooth, creamy product that is desired by consumers. • Isomerization of cis to trans fatty acids will occur during this process. • Current dietary advice includes reducing the consumption of saturated and trans fatty acids. TRIGLYCERIDE REACTION MAP WAXES • Waxes are esters of fatty acids and long chain alcohols (1232 carbon atoms). They are: • water insoluble and not easily hydrolyzed. • often found in protective coatings. • used commercially to make cosmetics, candles, ointments, and protective polishes. WAXES (continued) PHOSPHOGLYCERIDES • A phosphoglyceride is a phospholipid that contains glycerol, fatty acids, phosphoric acid, and an alcohol (usually an amino alcohol). PHOSPHOGLYCERIDES (continued) PHOSPHOGLYCERIDES (continued) • Lecithins: • contain the amino alcohol choline. • are an important cell membrane component. • are emulsifying and micelle-forming agents. • Cephalins: • contain ethanolamine or serine as the alcohol. • are found in most cell membranes, especially brain tissue and blood platelets (role in blood-clotting process). PHOSPHOGLYCERIDES (continued) • Phosphatidylcholine (lecithin): PHOSPHOGLYCERIDES (continued) • Cephalin: