Chapter 19 Lipids PDF

11/30/24 Chapter 19 Lipids 1 Chapter 19 Table of Contents 19.1 Structure and Classification of Lipids 19.2 Types of Fatty Acids 19.3...

11/30/24 Chapter 19 Lipids 1 Chapter 19 Table of Contents 19.1 Structure and Classification of Lipids 19.2 Types of Fatty Acids 19.3 Physical Properties of Fatty Acids 19.4 Energy-Storage Lipids: Triacylglycerols 19.5 Dietary Considerations and Triacylglycerols 19.6 Chemical Reactions of Triacylglycerols 19.7 Membrane Lipids: Phospholipids 19.8 Membrane Lipids: Sphingoglycolipids 19.9 Membrane Lipids: Cholesterol 19.10 Cell Membranes 19.11 Emulsification Lipids: Bile Acids 19.12 Messenger Lipids: Steroid Hormones 19.13 Messenger Lipids: Eicosanoids 19.14 Protective-Coating Lipids: Biological Waxes Copyright © Cengage Learning. All rights reserved 2 2 1  11/30/24 Section 19.1 Structure and Classification of Lipids Lipids A lipid is an organic compound found in living organisms that is insoluble (or only sparingly soluble) in water but soluble in non-polar organic solvents. Unlike other biomolecules, lipids do not have a common structural features that serves as the basis for defining such compounds. Classification: They are classified on the basis of solubility not on any functional groups – Insoluble or sparingly soluble in water – Soluble in non-polar organic solvents Return to TOC Copyright © Cengage Learning. All rights reserved 3 3 Section 19.1 Structure and Classification of Lipids Five Categories of Lipids For purposes of simplicity of study lipids are divided into five categories based on their function: – Energy-storage lipids - triacylglycerols – Membrane lipids - phospholipids, sphingoglycolipids, and cholesterol – Emulsification lipids - bile acids – Chemical messenger lipids - steroid hormones and eicosanoids) – Protective-coating lipids - biological waxes Return to TOC Copyright © Cengage Learning. All rights reserved 4 4 2  11/30/24 Section 19.1 Structure and Classification of Lipids Structural Formulas Lipids exhibit structural diversity Some are esters, some are amides, and some are alcohols (acyclic and cyclic) and some are polycyclic. Return to TOC Copyright © Cengage Learning. All rights reserved 5 5 Section 19.2 Types of Fatty Acids Saturated and Unsaturated Fatty Acids Carboxylic acids with linear (unbranched) carbon chain - Fatty acids are naturally occuring monocarboxylic acids Even # of Carbon atoms: – Long chain fatty acids: C12 - C26 – Medium chain fatty acids: C6 - C11 – Short-chain fatty acids: C4 - C5 Two Types: – Saturated - all C-C bonds are single bonds – Unsaturated – Monounsaturated: one C=C bond – Polyunsaturated: 2 or more C=C bonds present - up to six double bonds are present in fatty acids Return to TOC Copyright © Cengage Learning. All rights reserved 6 6 3  11/30/24 Section 19.2 Types of Fatty Acids Saturated Fatty Acids – Numbering starts from the end of -COOH group – See structural notation: it indicates number of C atoms – Example - Lauric acid has 12 C atoms and no double bonds so it is (12:0) Return to TOC Copyright © Cengage Learning. All rights reserved 7 7 Section 19.2 Types of Fatty Acids Unsaturated Fatty Acids A monounsaturated fatty acid is a fatty acid with a carbon chain in which one carbon–carbon double bond is present. Different ways of depicting the structure Return to TOC Copyright © Cengage Learning. All rights reserved 8 8 4  11/30/24 Section 19.2 Types of Fatty Acids Polyunsaturated Fatty Acids (PUFAs) A polyunsaturated fatty acid is a fatty acid with a carbon chain in which two or more carbon–carbon double bonds are present. Up to six double bonds are found in biochemically important PUFAs. Two types of unsaturated fatty acids. – Omega (ω)-3 fatty acids - An unsaturated fatty acid with its endmost double bond three carbon atoms away from its methyl end. – Omega(ω)-6 fatty acid is an unsaturated fatty acid with its endmost double bond six carbon atoms away from its methyl end. Return to TOC Copyright © Cengage Learning. All rights reserved 9 9 Section 19.2 Types of Fatty Acids Selected Unsaturated Fatty Acids of Biological Importance Numbering starts from the other end of COOH See structural notation: it indicates number of C atoms E.g., 18:2 – 18 carbons, 2 double bonds Return to TOC Copyright © Cengage Learning. All rights reserved 10 10 5  11/30/24 Section 19.2 Types of Fatty Acids Omega Acids Essential Fatty Acids: Must be part of diet Nutritionally important Omega-3 and Omega-6 fatty acids – Linolenic acid – Omega-3 – Linoleic acid – Omega-6 Linoleic Acid Deficiency: – Skin redness - becomes irritated – Infections and dehydration – Liver abnormalities – Children need it the most – Human milk has more than cow’s milk Return to TOC Copyright © Cengage Learning. All rights reserved 11 11 Section 19.2 Types of Fatty Acids American Diet Sufficient in omega 6 fatty acids Deficient in omega 3 fatty acids – Fish - good source for omega 3 fatty acids High rate of heart disease may be due to imbalance in omega 3 and 6 fatty acids – Ideal ratio: Omega 6 : Omega 3 (4 - 10 g: 1g) Return to TOC Copyright © Cengage Learning. All rights reserved 12 12 6  11/30/24 Section 19.3 Physical Properties of Fatty Acids Water solubility: Short chain fatty acids have some solubility whereas long chain fatty acids are insoluble – Short chain fatty acids are sparingly soluble because of carboxylic acid polar group Physical properties such as melting point depends on the number of C atoms and degree unsaturation Return to TOC Copyright © Cengage Learning. All rights reserved 13 13 Section 19.3 Physical Properties of Fatty Acids The Melting Point Melting Point Depends Upon: – Length of carbon chain – Degree of unsaturation (number of double bonds in a molecule) Return to TOC Copyright © Cengage Learning. All rights reserved 14 14 7  11/30/24 Section 19.2 Types of Fatty Acids Return to TOC Copyright © Cengage Learning. All rights reserved 15 15 Section 19.3 Physical Properties of Fatty Acids Space-Filling Molecules The number of bends in a fatty acid chain increase as the number of double bonds increase Less packing occurs Melting point is lower Tend to be liquids at room temperature Return to TOC Copyright © Cengage Learning. All rights reserved 16 16 8  11/30/24 Section 19.2 Types of Fatty Acids Return to TOC Copyright © Cengage Learning. All rights reserved 17 17 Section 19.4 Energy-Storage Lipids: Triacylglycerols Energy-Storage Materials With the notable exception of nerve cells, human cells store small amounts of energy providing materials: – The most widespread energy storage material - carbohydrate glycogen – Present in small amounts Storage material is the triacylglycerols: – Triacylglycerols are concentrated primarily in special cells (adipocytes) – Nearly filled with the material. Return to TOC Copyright © Cengage Learning. All rights reserved 18 18 9  11/30/24 Section 19.4 Energy-Storage Lipids: Triacylglycerols Two Types of Triacylglycerols Simple Triacylglycerols: Three identical fatty acids are esterified – Naturally occurring simple triacylglycerols are rare Mixed Triacylglycerols: A triester formed from the esterification of glycerol with more than one kind of fatty acid – In nature mostly mixed triacylglycerols are found and are different even from the same source depending on the feed, e.g., corn, peanut and wheat -fed cows have different triacylglycerols Return to TOC Copyright © Cengage Learning. All rights reserved 19 19 Section 19.4 Energy-Storage Lipids: Triacylglycerols Difference of Fats and Oils Physical State: – Fats Predominantly Saturated Solids or semisolids at room temperature – Oils: Predominantly unsaturated Liquids at room temperature Source: – Fats: Animal source and tasteless – Oils: Plants and fish oil – Pure oils and fats are colorless, odorless Return to TOC Copyright © Cengage Learning. All rights reserved 20 20 10  11/30/24 Section 19.5 Dietary Considerations and Triacylglycerols Studies Nations whose citizens have high dietary intakes of fats and oils tend to have higher incidences of heart disease and certain types of cancers Typical American diet contains too much fat and therefore the Americans are being asked to reduce their total dietary fat intake Other studies show that risk factor is more than simply the total amount of triacylglycerols consumed Return to TOC Copyright © Cengage Learning. All rights reserved 21 21 Section 19.5 Dietary Considerations and Triacylglycerols “Good Fats” Versus “Bad Fats” Studies indicate that type of dietary fat and amount of dietary fat are important for balanced diet: – Current recommended amounts are: total fat intake in calories: 15% - Monounsaturated fat 10% - Polyunsaturated