Lecture 15 lipids can be taught
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The document summarizes key aspects of lipids. It describes the main classes of lipids, including fatty acids, triacylglycerols, glycerophospholipids, sphingolipids, steroids, and eicosanoids. It also discusses the main biological functions of lipids as essential components of biological membranes, as energy stores, and in cell signaling. Key lipid structures are presented, along with enzymatic pathways involved in lipid biosynthesis and metabolism.
Lecture 15 lipids can be taught
- 1. Lipids • Fatty Acids • Triacylglycerols • Glycerophospholipids • Sphingolipids • Steroids, Eicosanoids • Lipid Bilayers Lipids consist of hydrophobic molecules that have great structural variability and are not polymeric. In general, the lipids perform three biological functions: 1. Essential components of biological membranes. 2. Contain hydrocarbon chains that serve as energy stores. 3. Involved in many intracellular and intercellular signaling.
- 2. Fatty Acids Fatty acids are carboxylic acids with long-chain hydrocarbon side groups. In plants and animals, the predominant fatty acid residues have C16 or C18 side chains. Type of Fatty Acid Saturated Fatty Acids Unsaturated Fatty Acids Polyunsaturated Fatty Acids Content of Side Chain no double bonds contain double bonds contain 2 or more double bonds
- 3. Common C18 Fatty Acids HOOC CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 CH2 1 HOOC 18 HOOC 1 9 18 HOOC 1 18 9 HOOC 1 18 9 12 12 15 Stearic Acid 18:0 Oleic Acid 18:1 Linoleic Acid 18:2 a-Linolenic Acid 18:3 Fatty acid double bonds are almost always have a cis configuration.
- 4. Table 9-1. Common Biological Fatty Acids Common Name Systematic Name Structure Saturated fatty acids 12:0 Lauric acid Dodecanoic acid CH3(CH2)10COOH 14:0 Myristic acid Tetradecanoic acid CH3(CH2)12COOH 16:0 Palmitic acid Hexadecanoic acid CH3(CH2)14COOH 18:0 Stearic acid Octadecanoic acid CH3(CH2)16COOH 20:0 Arachidic acid Eicosanoic acid CH3(CH2)15COOH 22:0 Behenic acid Docosanoic acid CH3(CH2)20COOH 24:0 Lignoceric acid Tetracosanoic acid CH3(CH2)22COOH Unsaturated fatty acids (all double bonds are cis) 16:1 Palmitoleic acid 9-Hexadecenoic acid CH3(CH2)5CH=CH(CH2)7COOH 18:1 Oleic acid 9-Octadecenoic acid CH3(CH2)7CH=CH(CH2)7COOH 18:2 Linoleic acid 9,12-Octadecadienoic acid CH3(CH2)4(CH=CHCH2)2(CH2)6COOH 18:3 a-Linolenic acid 9,12,15-Octadecatrienoic acid CH3CH2(CH=CHCH2)3(CH2)6COOH 18:3 -Linolenic acid 6,9,12-Octadecatrienoic acid CH3(CH2)4(CH=CHCH2)3(CH2)3COOH 20:4 Arachidonic acid 5,8,11,14-Eicosatetraenoic acid CH3(CH2)4(CH=CHCH2)4(CH2)2COOH 20:5 EPA 5,8,11,14,17-Eicosapentaenoic acid CH3CH2(CH=CHCH2)5(CH2)2COOH 24:1 Nervonic acid 15-Tetracosenoic acid CH3(CH2)7CH=CH(CH2)13COOH
- 5. Triacylglycerols H2C HC H2C OH OH OH H2C HC H2C O O O O C R1 O C R2 O C R3 Glycerol Triacylglycerol O C H2C HC H2C O O O O C O 18 C 18 16 1-palmitoleoyl-2-linoleoyl-3-stearoyl-glycerol 1 2 3
- 6. Fats and Oils - Energy Reserves Fats and oils exist primarily as triacylglycerols (or triglycerides). Fats are solids at room temperature, oils are liquids. Fats and oils are complex mixtures of triacylglycerols (composition) varies with organism). Plant oils are richer in unsaturated fatty acids (lower melting point and thus are liquids at room temperature). Fats are a highly efficient form of energy. Fats are less oxidized than proteins or carbohydrates and thus produce more energy per unit mass upon complete oxidation. Also, fats are stored anhydrous. Fats provide about six times the metabolic energy of an equal weight of hydrated glycogen. Adipocytes (fat cells) synthesize and store triacylglycerols and adipose tissue is the most abundant tissue source.
- 7. Glycerophospholipids (or phosphoglycerides) • major component of biological membranes • esters of glycerol-3-phosphate O O C R1 O Amphiphilic molecules: nonpolar aliphatic (hydrocarbon) “tails” polar phosphoryl-X “heads” H2C C H2C OH H O HO P OH OH H2C C H2C O H O O P O O-O R2 C X L-glycerol-3-phosphate general structure of a glycerophospholipid
- 8. Common Classes of Phospholipids X-OH water ethanolamine choline serine glycerol O Formula of -X -H -CH2CH2NH3 + -CH2CH2N(CH3)3 + -CH2CH(NH3 +)COO- -CH2CH(OH)CH2OH O C R1 Name phosphatidic acid phosphatidylethanolamine phosphatidylcholine (lecithin) phosphatidylserine phosphatidylglycerol Table 9-2. H2C C H2C O H O O P O O-O R2 C X
- 9. Structure of a Phospholipid 1-stearoyl-2-oleoyl-3-phosphatidylcholine Fig. 9-4 H2C C H2C O H O O O C P O O-O (CH2)16CH3 O C (CH2)7 CH2CH2N(CH3)3 + H C H C(CH2)7 H3C
- 10. Phospholipases hydrolyze phospholipids. phospholipase A2 O C R1 O phospholipase A2 phospholipase A1 O C R1 O C R1 O phospholipase C phospholipase D H2C C H2C O H O O P O O-O R2 C X H2C C H2C O H O HO P O O-O X H2O R2COOH H2C C H2C O H O O P O O-O R2 C X
- 11. Phospholipases A2 - phospholipid complex Fig. 9-6
- 12. Sphingolipids • a major membrane component • derivatives of the C18 amino alcohol sphingosine • N-acyl fatty acid derivatives are known as ceramides OH OH H H2C C C H CH +H3N HC (CH2)12 CH3 sphingosine OH OH H H2C C C H CH HN HC (CH2)12 CH3 C R ceramide O (R = fatty acid residue)
- 13. Steroids A B C D cyclopentanoperhydrophenanthrene
- 14. Cholesterol HO cholesterol Central steroid in the animal kingdom Two Functions: • Serves as an integral component in biological membranes • Serves as the biosynthetic precursor to other steroid molecules
- 15. Adrenal Steroidogenesis HO cholesterol HO O pregnenolone side chain cleavage HO OH O O OH HO OH O O O cortisol aldosterone
- 16. Sex Hormone Steroidogenesis HO cholesterol HO O pregnenolone side chain cleavage OH O O progesterone HO OH aromatase O estradiol testosterone
- 17. Eicosanoids • Eicosanoids (C20) are derived from arachidonic acid (20:4) • Four classes of eicosanoids: – prostaglandins – prostacyclins – thromboxanes – leukotrienes 1 COOH 8 5 11 14 20 arachidonic acid (5,8,11,14-eicosatetraenoic acid)
- 18. Eicosanoid Biosynthesis COOH arachidonic acid phospholipids phospholipase A2 cyclooxygenase 5-lipooxygenase O O COOH OH PGH2 COOH OH OH LTB4 (leukotriene) COOH OH HO HO COOH OH O HO COOH OH HO HO O PGF2a (prostaglandin) PGI2 (prostacyclin) TxB2 (thromboxane)
Editor's Notes
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