Biochem 1A Sept 23 Lecture Notes PDF

Section 19.1 Structure and Classification of Lipids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 1  Chapter 19 Chapter Outline 19.1 Structure and classification of lipids...

Section 19.1 Structure and Classification of Lipids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 1  Chapter 19 Chapter Outline 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 19.15 Saponifiable and nonsaponifiable lipids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 2  Section 19.1 Structure and Classification of Lipids Lipids Lipid: 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 feature that serves as the basis for defining such compounds Classification is based on two methods – Biochemical function – Saponification Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 3  Section 19.1 Structure and Classification of Lipids Classification based on Biochemical Function For purposes of simplicity of study, lipids are divided into five categories based on their biochemical function: – Energy-storage lipids (triacylglycerols) – Membrane lipids (phospholipids, sphingoglycolipids, and cholesterol) – Emulsification lipids (bile acids) – Messenger lipids (steroid hormones and eicosanoids) – Protective-coating lipids (biological waxes) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 4  Section 19.1 Structure and Classification of Lipids Classification Based on Saponification Saponification reaction - Hydrolysis reaction that occurs in a basic solution Based on saponification reactions, lipids are divided into two categories: – Saponifiable lipids (triacylglycerols, phospholipids, sphingoglycolipids, cholesterol, and biological waxes) – Nonsaponifiable lipids (bile acids, steroid hormones, and eicosanoids) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 5  Section 19.1 Structure and Classification of Lipids Structural Diversity of Lipids Lipids exhibit structural diversity Some are esters, some are amides, and some are alcohols (acyclic, cyclic, and polycyclic) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 6  Section 19.1 Structure and Classification of Lipids Figure 19.1 - Structural Formula of Types of Lipids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 7  Section 19.1 Structure and Classification of Lipids A lipid is an organic compound found in living organisms that is: a.soluble in water and insoluble in nonpolar organic solvents. b.soluble in water and soluble in nonpolar organic solvents. c.insoluble in water and insoluble in nonpolar organic solvents. d.insoluble in water and soluble in nonpolar organic solvents. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 8  Section 19.1 Structure and Classification of Lipids A lipid is an organic compound found in living organisms that is: a.soluble in water and insoluble in nonpolar organic solvents. b.soluble in water and soluble in nonpolar organic solvents. c.insoluble in water and insoluble in nonpolar organic solvents. d.insoluble in water and soluble in nonpolar organic solvents. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 9  Section 19.2 Types of Fatty Acids Fatty Acids - An Introduction Fatty acids: Naturally occurring monocarboxylic acids (COOH) with linear (unbranched) carbon chain – Have even number of carbon atoms Long-chain fatty acids (C12 to C26) Medium-chain fatty acids (C8 to C10) Short-chain fatty acids (C4 to C6) Two types: – Saturated - All C–C bonds are single bonds – Unsaturated Monounsaturated Return to TOC Learning. Copyright ©2016 Cengage Polyunsaturated All Rights Reserved. 10  Section 19.2 Types of Fatty Acids Saturated Fatty Acids Fatty acids with a carbon chain in which all C–C bonds are single bonds Numbering starts from the end of –COOH group Consider the structural notations for palmitic acid: Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 11  Section 19.2 Types of Fatty Acids Unsaturated Fatty Acids Monounsaturated fatty acid: Fatty acid with a carbon chain in which one carbon–carbon double bond is present There are different ways of depicting the structure 6,8,13 1 8 : Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 3 12  Section 19.2 Types of Fatty Acids Polyunsaturated Fatty Acids (PUFAs) Fatty acids 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 13  Section 19.2 Types of Fatty Acids Double-Bond Position in Unsaturated Fatty Acids Numbering starts from the other end of –COOH Structural notation indicates number of C atoms Example: – 18:2 signifies that a fatty acid has 18 carbons with 2 double bonds 3, 7, 15 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 14  Section 19.2 Types of Fatty Acids Types of Unsaturated Fatty Acids Omega (ω)-3 fatty acid: Unsaturated fatty acid with its endmost double bond three carbon atoms away from its methyl end Omega (ω)-6 fatty acid: Unsaturated fatty acid with its endmost double bond six carbon atoms away from its methyl end Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 15  Section 19.2 Types of Fatty Acids A fatty acid is a naturally occurring _____ acid that nearly always contains an _____ number of carbon atoms with a carbon chain that is _____. a.monocarboxylic; even; branched b.dicarboxylic; odd; unbranched c.monocarboxylic; even; unbranched d.dicarboxylic; even; branched Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 16  Section 19.2 Types of Fatty Acids A fatty acid is a naturally occurring _____ acid that nearly always contains an _____ number of carbon atoms with a carbon chain that is _____. a.monocarboxylic; even; branched b.dicarboxylic; odd; unbranched c.monocarboxylic; even; unbranched d.dicarboxylic; even; branched Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 17  Section 19.2 Types of Fatty Acids Be back at 8:25 10 MINS SCREEN BREAK Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 18  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 the presence of carboxylic group Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 19  Section 19.3 Physical Properties of Fatty Acids Melting Point Depends upon the following: – Length of carbon chain – Degree of unsaturation (number of double bonds in a molecule) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 20  Section 19.3 Physical Properties of Fatty Acids Number of “bends” in a fatty acid chain increases as the number of double bonds increases Less packing occurs Melting point is lower Tend to be liquid at room temperature Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 21  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 – Carbohydrate glycogen - Most widespread energy storage material present in small amounts Major energy-storage material is triacylglycerol – Concentrated primarily in special cells (adipocytes) which are nearly filled with triacylglycerols Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 22  Section 19.4 Energy-Storage Lipids: Triacylglycerols H - O--C=O CH2-O H CH - O H CH2-O H Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 23  Section 19.4 Energy-Storage Lipids: Triacylglycerols Two Types of Triacylglycerols Simple triacylglycerol: Triester formed from the esterification if glycerol with three identical fatty acid molecules – Naturally occurring simple triacylglycerols are rare Mixed triacylglycerol: Triester formed from the esterification of glycerol with more than one kind of fatty acid molecule Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 24  Section 19.4 Energy-Storage Lipids: Triacylglycerols Fats and Oils Fats: – Predominantly Saturated – Solids or semisolids at room temperature – Source: Animals Oils: – Predominantly unsaturated – Liquids at room temperature – Sources: Plants and fish oil Pure oils and fats are colorless, odorless, and tasteless Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 25  Section 19.5 Dietary Considerations and Triacylglycerols Studies Concerning Role of Dietary Factors as a Cause of Disease 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 – Americans are being asked to reduce their total dietary fat intake Other studies show that risk factors involve more than simply the total amount of triacylglycerols consumed Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 26  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 to determine body responses to dietary fat Current recommended amount for total fat intake in calories: – 15% - Monounsaturated fat – 10% - Polyunsaturated –