1 Chapter 15: Lipids Chem 20 El Camino College

2 Lipids Lipids are a family of biomolecules that are not soluble in water but can be extracted by organic solvents of low polarity like ether or chloroform. There are two kinds of lipids, one with fatty acids and one without fatty acids called steroids.

3 Lipids Lipids that have fatty acids are waxes, triacylglycerols, glycerophospholipids and prostaglandins Steroids are characterized by the steroid nucleus of four fused carbon rings.

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5 Fatty Acids With only few exceptions, the fatty acids are all straight-chain compounds containing an even number of carbons ( the molecules are built up two carbons at a time from acetate units). They consist of long carbon chains attached to a carboxylic acid group

6 Fatty Acids

7 Saturated fatty acids only contain single bonds on the carbon chain Mono-unsaturated fatty acids contain one double bond on the carbon chain Poly-unsaturated fatty acids contain two or more double bonds on the carbon chain

8 Saturated Fatty Acids Lauric acid (12 C) CH 3 -(CH 2 ) 10 –COOH Myristic acid (14 C) CH 3 -(CH 2 ) 12 –COOH Palmitic acid (16 C) CH 3 -(CH 2 ) 14 –COOH Stearic acid (18 C) CH 3 -(CH 2 ) 16 –COOH

9 Unsaturated Fatty Acids Oleic acid (18 C) CH 3 -(CH 2 ) 7 - CH =CH-(CH 2 ) 7 -COOH Linoleic Acid (18 C) CH 3 -(CH 2 ) 4 - CH =CH-CH 2 -CH =CH-(CH 2 ) 7 – COOH

10 Unsaturated Fatty Acids Linolenic Acid (18 C) CH 3 -CH 2 – (CH =CH-CH 2 ) 3 -(CH 2 ) 6 –COOH Arachidonic Acid (20 C) CH 3 –(CH 2 ) 3 – (CH 2 -CH =CH) 4 -(CH 2 ) 3 –COOH

11 Unsaturated Fatty Acids configuration is almost invariably cis. (cis isomer has lower melting point than trans, making the cell membrane semiliquid). Linoleic acid, linolenic acid and arachidonic acid are called essential fatty acids, because they must be obtained from the diet.

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14 Fatty Acids Draw stearic acid, a saturated fatty acid found in animal fat containing 18 carbons

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16 Triacylglycerols: Fats & Oils Fatty acids are stored in the body as triacylglycerols (also called triglycerides) These molecules have three ester groups connecting fatty acids to glycerol

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19 Triacylglycerols: Fats & Oils In an esterification reaction, an alcohol reacts with a carboxylic acid This is the same reaction that makes triglycerides

20 Triacylglycerols: Fats & Oils Some triglycerides contain 3 different fatty acids Draw a triglyceride containing the following fatty acids in any order

21 Hydrogenation of oil Although unsaturated fats are healthier, they are liquid By doing a hydrogenation reaction to unsaturated fats, some of the C=C double bonds become single bonds This makes a creamier, appealing-looking product that clogs arteries Margarine, vegetable shortening, and the “creme” fillings in cakes and cookies have been partially hydrogenated.

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23 Making Saturated Fats Glyceryl trioleate can react with hydrogen in the presence of a Pt catalyst to form glyceryl tristearate

24 Hydrolysis of Fats Triacylglycerols are hydrolyzed in the presence of strong acids or enzymes to produce glycerol and fatty acids.

25 Soap Soap is made by heating fat with a strong base such as NaOH, KOH.

26 Micelles Micelles are spherical clusters containing hundreds of soap molecules. The non-polar hydrocarbon chains ‘dissolve” in each other. The polar –COO - groups dissolve in water. Similarly charged micelles repel each other..

27 Micelles The cleansing property of soap is due to the dissolution of non-polar ends of soap molecules in oil droplets forming a stable emulsion of oil and water.

28 Wax Wax is an ester of a saturated fatty acid and a long-chain alcohol. Beeswax CH 3 -(CH 2 ) 14 –CO-O-(CH 2 ) 29 -CH 3 Carnaubawax CH 3 -(CH 2 ) 24 –CO-O-(CH 2 ) 29 -CH 3

29 Prostaglandins Prostaglandins are hormone-like substances, produced from arachidonic acid. They have 5 carbon ring and 20 carbon atoms including a 5 carbon ring. They have important functions in body.

30 Glycerophospholipids Phospholipids are similar to triglycerides, except except that one –OH of glycerol is replaced by the ester of phosphoric acid and an amino alcohol bonded though a phosphodiester bond. They are an important component of cell membranes They make up much of the fatty coating of nerve cells (called the myelin sheath) They combine with triglycerides and cholesterol to make them more soluble.

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32 Glycerophospholipids Note the phosphate gp and amine gps have charges Given a drawing, you should be able to identify a phospholipid

33 Glycerophospholipids The amino alcohols are most often ethanolamine, choline.

34 Steroids Steriods contain a steroid nucleus Memorize the structure of the steroid nucleus

35 Steroids Biologically important steroids include cholesterol, testosterone, estrogen, progesterone, and cortisone Some steroids are hormones, or chemical messenger molecules in the body Derivatives of testosterone are called anabolic steroids. These illegal substances increase muscle mass, but they also are toxic to the body.

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37 Cell Membranes Phospholipids are a major component of cell membranes They have polar “heads” and nonpolar “tails” In a membrane, the polar heads face the outside, and the nonpolar tails face the inside

38 Cell Membranes

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