Chapter 18: Lipids

CHEM 1152

Dr. Sheppard

Spring 2015

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Lipids

• One of 4 major classes of compounds found in living tissue– Nucleic acids, proteins, carbohydrates, lipids

• Specific types differ in structure• Includes fats, oils, cholesterol• Insoluble in water (large nonpolar section)• Soluble in organic solvents • Energy storage• Cell membranes• Insulation• Hormones/messengers• Some vitamins

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18.1 Classification of lipids

Saponifiable = estersSimple = two components (fatty acid and alcohol)Complex = more than two components

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Some example lipid structures

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18.2 Fatty acids (FAs)

• Simplest type of lipid• Component of other more complex lipids• Carboxylic acid with long (10-20) carbon chain

– Even number of carbons– Typically unbranched

C C C C C C C C C C C C C C C OHC

OH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

OH

O

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Fatty acids and micelle formation

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Saturated vs. unsaturated fatty acids

• Saturated (“bad” fat)– Only C─C– Highly flexible– Pack together

• Unsaturated (“good” fat)– Contains C═C– Cis double bonds– “Kink” in chain reduces

possibility of heart disease• Don’t stick to walls of blood

vessels• Promote blood flow

– Monounsaturated – Polyunsaturated

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Essential fatty acids

• Not synthesized by the body • Needed as precursors for essential molecules• Must be obtained from the diet• Plant and fish oils• Linoleic acid (18 carbons, 2 double bonds)• Linolenic acid (18 carbons, 3 double bonds)

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Some important unsaturated fatty acids

• Oleic acid (18:1)– Olives– 18 carbons, C=C at C9

• Linoleic (18:2)– Corn, soybean oil– Essential FA– Omega-6 FA

• Linolenic acid (18:3)– Corn, fish oil– Essential FA– Omega-3 FA

1

18

9

O

OH

1

18

O

OH

1

18

O

OH

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Physical properties of fatty acids

• Solubility– Insoluble in water– Soluble in organic solvents

(ether, chloroform)

• Melting point– Saturated = solid at room

temperature– MP increases with longer

chains– MP decreases with number

of unsaturations

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18.3 Structure of Fats and oils

• Triglycerides/triacylglycerols (TAGs) – Most abundant class of lipids in animals – Fatty acid triesters of glycerol– Formed from esterification

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Triglycerides

• Function– Energy reserves– Insulation

• Stored in adipocytes throughout the body– Hydrolyzed as needed by

enzymes called lipases

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Triglycerides

• Mixed vs. simple• mp determined by degree of unsaturation

– More unsaturation in plants than in animals– “Fat” = mostly saturated

• Solid at room temperature• Meat, butter (animal sources other than fish)

– “Oil” = mostly unsaturated• Liquid at room temperature• Olive oil, peanut oil (fish and plants)

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Triglycerides

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Mixed or simple? Fat or oil?