Chapter 26

Chapter 26 - Chapter 26 Lipids Dr. Wolf's CHM 424 26- 1...

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Unformatted text preview: Chapter 26 Lipids Dr. Wolf's CHM 424 26- 1 Lipids Lipids are naturally occurring substances Lipids grouped together on the basis of a common property—they are more soluble in nonpolar solvents than in water. solvents Some of the most important of them—the ones Some in this chapter—are related in that they have acetic acid (acetate) as their biosynthetic origin. acetic In many biosynthetic pathways a substance In called acetyl coenzyme A serves as the source of acetate. of Dr. Wolf's CHM 424 26- 2 26.1 Acetyl Coenzyme A Dr. Wolf's CHM 424 26- 3 Structure of Coenzyme A OO HO O HO P HO O O HO O N P O OH P O H3C H H N OH N CH3 O O N NH 2 N N R = H; Coenzyme A O R = CCH3; Acetyl coenzyme A Dr. Wolf's CHM 424 26- 4 SR Reactivity of Coenzyme A Nucleophilic acyl substitution O CH3CSCoA HY • • O CH3C Y • + HSCoA • Acetyl coenzyme A is a source of an acetyl Acetyl group toward biological nucleophiles; iit is an nucleophiles t acetyl transfer agent. acetyl Dr. Wolf's CHM 424 26- 5 Reactivity of Coenzyme A can react via enol O OH H2C CH3CSCoA Acetyl coenzyme A reacts Acetyl with biological electrophiles at its α electrophiles carbon atom. carbon Dr. Wolf's CHM 424 CSCoA E+ O E CH2CSCoA 26- 6 26.2 Fats, Oils, and Fatty Acids Dr. Wolf's CHM 424 26- 7 Fats and Oils O O CH2OCR' RCOCH CH2OCR" O Fats and oils are naturally occurring mixture of Fats triacylglycerols (also called triglycerides). triacylglycerols Fats are solids; oils are liquids. Dr. Wolf's CHM 424 26- 8 Fats and Oils O O CH2OC(CH2)16CH3 CH3(CH2)16COCH CH2OC(CH2)16CH3 O Tristearin; mp 72°C Dr. Wolf's CHM 424 26- 9 Fats and Oils O O CH3(CH2)6CH2 C H CH2OC(CH2)16CH3 CH2(CH2)6COCH C CH2OC(CH2)16CH3 H O 2-Oleyl-1,3-distearylglycerol; mp 43°C Dr. Wolf's CHM 424 26- 10 Fats and Oils 2-Oleyl-1,3-distearylglycerol mp 43°C H2, Pt Tristearin mp 72°C Dr. Wolf's CHM 424 26- 11 Fatty Acids O O O CH2OCR O H2O R'COCH CH2OCR" R'COH CH2OH HOCR HOCH CH2OH HOCR" O O Acids obtained by the hydrolysis of fats and oils are called Acids fatty acids. Fatty acids usually have an unbranched chain with an even number of carbon atoms. number If double bonds are present, they are almost always cis. Dr. Wolf's CHM 424 26- 12 Table 26.1 O CH3(CH2)10COH Systematic name Common name Dodecanoic acid Lauric acid O CH3(CH2)12COH Tetradecanoic acid Myristic acid O CH3(CH2)14COH Dr. Wolf's CHM 424 Hexadecanoic acid Palmitic acid 26- 13 Table 26.1 O CH3(CH2)16COH Systematic name Common name Octadecanoic acid Stearic acid Icosanoic acid Arachidic acid O CH3(CH2)18COH Dr. Wolf's CHM 424 26- 14 Table 26.1 O CH3(CH2)7 (CH2)7COH C H C H Systematic name: (Z)-9-Octadecenoic acid Common name: Oleic acid Dr. Wolf's CHM 424 26- 15 Table 26.1 O CH3(CH2)4 C H (CH2)7COH CH2 C C HH C H Systematic name: (9Z, 12Z)-9,12-Octadecadienoic acid Common name: Linoleic acid Dr. Wolf's CHM 424 26- 16 Table 26.1 O CH3CH2 C H C C HH Systematic name: Systematic (CH2)7COH CH2 CH2 C C HH C H (9Z, 12Z, 15Z)-9,12,15(9 Octadecatrienoic acid Common name: Linolenic acid Dr. Wolf's CHM 424 26- 17 Table 26.1 O OH H H H H H H H Systematic name: Systematic H (5Z, 8Z, 11Z, 14Z)-5,8,11,14(5Z, Icosatetraenoic acid Common name: Arachidonic acid Dr. Wolf's CHM 424 26- 18 trans-Fatty Acids Are formed by isomerization that can occur Are when esters of cis-fatty acids are hydrogenated. when H O H OR H2, cat O OR Dr. Wolf's CHM 424 26- 19 H O OR H H O H OR H2, cat O OR Dr. Wolf's CHM 424 26- 20 26.3 Fatty Acid Biosynthesis Dr. Wolf's CHM 424 26- 21 Fatty Acid Biosynthesis Fatty acids are biosynthesized via acetyl Fatty coenzyme A. coenzyme The group of enzymes involved in the overall The process is called fatty acid synthetase. fatty One of the key components of fatty acid One synthetase is acyl carrier protein (ACP—SH). (ACP—SH). Dr. Wolf's CHM 424 26- 22 Fatty Acid Biosynthesis An early step in fatty acid biosynthesis is the An reaction of acyl carrier protein with acetyl coenzyme A. coenzyme O CH3CSCoA + HS—ACP O CH3CS—ACP + HSCoA Dr. Wolf's CHM 424 26- 23 Fatty Acid Biosynthesis A second molecule of acetyl coenzyme A reacts second at its α carbon atom with carbon dioxide (as HCO3–) to give malonyl coenzyme A. HCO O – CH3CSCoA + HCO3 Acetyl coenzyme A Dr. Wolf's CHM 424 O O – OCCH2CSCoA Malonyl coenzyme A 26- 24 Fatty Acid Biosynthesis Malonyl coenzyme A then reacts with acyl Malonyl carrier protein. carrier O O O – OCCH2CS—ACP ACP—SH O – OCCH2CSCoA Malonyl coenzyme A Dr. Wolf's CHM 424 26- 25 Fatty Acid Biosynthesis Malonyl—ACP and acetyl—ACP react by Malonyl—ACP carbon-carbon bond formation, accompanied by decarboxylation. decarboxylation. O S—ACP CH3C –• •• •O •• O C O CH2CS—ACP Dr. Wolf's CHM 424 O CH3C O CH2CS—ACP CH S-Acetoacetyl—ACP 26- 26 Fatty Acid Biosynthesis In the next step, the ketone carbonyl is reduced In to a secondary alcohol. to OH CH3C O CH2CS—ACP H Dr. Wolf's CHM 424 NADPH O CH3C O CH2CS—ACP S-Acetoacetyl—ACP 26- 27 Fatty Acid Biosynthesis The alcohol then dehydrates. OH CH3C O CH2CS—ACP O CH3CH CHCS—ACP H Dr. Wolf's CHM 424 26- 28 Fatty Acid Biosynthesis Reduction of the double bond yields ACP bearing an attached butanoyl group. Repeating the process gives a 6-carbon acyl Repeating group, then an 8-carbon one, then 10, etc. group, O CH3CH2CH2CS—ACP Dr. Wolf's CHM 424 O CH3CH CHCS—ACP 26- 29 26.4 Phospholipids Dr. Wolf's CHM 424 26- 30 Phospholipids Phospholipids are intermediates in the Phospholipids biosynthesis of triacylglycerols. biosynthesis The starting materials are L-glycerol 3The phosphate and the appropriate acyl coenzyme A phosphate molecules. molecules. Dr. Wolf's CHM 424 26- 31 CH2OH HO H O + O RCSCoA + R'CSCoA CH2OPO3H2 The diacylated The species formed in this step is O called a phosphatidic R'CO acid. acid Dr. Wolf's CHM 424 O CH2OCR H CH2OPO3H2 26- 32 O O R'CO CH2OCR H CH2OH H2O The The phosphatidic acid then O undergoes hydrolysis of its R'CO phosphate ester function. function. Dr. Wolf's CHM 424 O CH2OCR H CH2OPO3H2 26- 33 O O R'CO H CH2OH O R"CSCoA O R'CO Dr. Wolf's CHM 424 CH2OCR O Reaction with a Reaction third acyl coenzyme A molecule yields the triacylglycerol. triacylglycerol. CH2OCR H O CH2OCR" 26- 34 Phosphatidylcholine Phosphatidic acids are intermediates in the Phosphatidic formation of phosphatidylcholine. phosphatidylcholine O O O R'CO CH2OCR H CH2OPO3H2 Dr. Wolf's CHM 424 O R'CO CH2OCR H – CH2OPO2 + (CH3)3NCH2CH2O 26- 35 Phosphatidylcholine O O R'CO hydrophobic "tail" CH2OCR hydrophobic "tail" H – CH2OPO2 + (CH3)3NCH2CH2O polar "head group" Dr. Wolf's CHM 424 26- 36 Phosphatidylcholine hydrophobic (lipophilic) "tails" hydrophilic "head group" Dr. Wolf's CHM 424 26- 37 Cell Membranes water Cell membranes are Cell "lipid bilayers." Each layer has an assembly of phosphatidyl choline molecules as its main structural component. component. Dr. Wolf's CHM 424 water 26- 38 Cell Membranes water The interior of the cell The membrane is hydrocarbon-like. Polar materials cannot pass from one side to the other of the membrane. membrane. Dr. Wolf's CHM 424 water 26- 39 26.5 Waxes Dr. Wolf's CHM 424 26- 40 Waxes Waxes are water-repelling solids that coat the Waxes leaves of plants, etc. leaves Structurally, waxes are mixtures of esters. The Structurally, esters are derived from fatty acids and longesters chain alcohols. O CH3(CH2)14COCH2(CH2)28CH3 Triacontyl hexadecanoate: occurs in beeswax Dr. Wolf's CHM 424 26- 41 26.6 Prostaglandins Dr. Wolf's CHM 424 26- 42 Prostaglandins Prostaglandins are involved in many biological Prostaglandins processes. processes. Are biosynthesized from linoleic acid (C18) via via arachidonic acid (C20). (See Table 26.1) arachidonic Dr. Wolf's CHM 424 26- 43 Examples: PGE1 and PGF1α and O O OH HO OH O HO HO OH HO Dr. Wolf's CHM 424 PGE1 OH PGF1α 26- 44 Prostaglandin Biosynthesis PGE2 is biosynthesized from arachidonic acid The oxygens come from O2 The enzyme involved (prostaglandin endoperoxide The synthase) has cyclooxygenase (COX) acitivity synthase) Dr. Wolf's CHM 424 26- 45 Prostaglandin Biosynthesis CO2H CH3 Arachidonic acid O2 fatty acid cyclooxygenase O CO2H O HOO Dr. Wolf's CHM 424 PGG2 PGG CH3 26- 46 Prostaglandin Biosynthesis O CO2H O HO PGH2 CH3 reduction of hydroperoxide O CO2H O HOO Dr. Wolf's CHM 424 PGG2 CH3 26- 47 Prostaglandin Biosynthesis O CO2H O HO O CH3 CO2H CH3 HO Dr. Wolf's CHM 424 PGH2 HO PGE2 26- 48 Icosanoids Icosanoids are compounds related to icosanoic acid CH3(CH2)18CO2H. Icosanoids include: prostaglandins thromboxanes prostacyclins leukotrienes Dr. Wolf's CHM 424 26- 49 Thromboxane A2 (TXA2) Thromboxane A2 is biosynthesized from PGH2 O CO2H O HO PGH2 CH3 TXA2 promotes platelet aggregation and blood clotting aggregation O CO2H O HO Dr. Wolf's CHM 424 TXA2 CH3 26- 50 Prostacyclin I2 (PGI2) Like thromboxane A2, prostacyclin I2 is biosynthesized from PGH2 HO2C HO O PGI2 inhibits platelet aggregation and relaxes aggregation coronary arteries CH3 HO Dr. Wolf's CHM 424 OH PGI2 26- 51 Leukotriene C4 (LTC4) Leukotrienes arise from arachidonic acid via a different biosynthetic pathway. They are the substances most responsible for constricting bronchial passages during asthma attacks. Dr. Wolf's CHM 424 26- 52 Leukotriene C4 (LTC4) OH OH CO2H O S CH3 CH2CHCNHCH2CO2H – O2CCHCH2CH2 NH C O + NH3 Dr. Wolf's CHM 424 26- 53 26.7 Terpenes: The Isoprene Rule Dr. Wolf's CHM 424 26- 54 Terpenes Terpenes are natural products that are Terpenes structurally related to isoprene. structurally CH3 H2C C CH CH2 or or Isoprene (2-methyl-1,3-butadiene) Dr. Wolf's CHM 424 26- 55 Terpenes Myrcene (isolated from oil of bayberry) Myrcene is a typical terpene. is CH3 CH3C CH2 CHCH2CH2CCH CH2 or or Dr. Wolf's CHM 424 26- 56 The Isoprene Unit An isoprene unit is the carbon skeleton of An isoprene (ignoring the double bonds) isoprene Myrcene contains two isoprene units. Myrcene Dr. Wolf's CHM 424 26- 57 The Isoprene Unit The isoprene units of myrcene are joined "headto-tail." head head tail tail head Dr. Wolf's CHM 424 26- 58 Table 26.2 Classification of Terpenes Class Monoterpene Sesquiterpene Diterpene Sesterpene Triterpene Tetraterpene Dr. Wolf's CHM 424 Number of carbon atoms 10 15 20 25 30 40 26- 59 Figure 26.6 Representative Monoterpenes OH OH O H α-Phellandrene Menthol (eucalyptus) (peppermint) Dr. Wolf's CHM 424 Citral (lemon grass) 26- 60 Figure 26.6 Representative Monoterpenes OH OH O H α-Phellandrene Menthol (eucalyptus) (peppermint) Dr. Wolf's CHM 424 Citral (lemon grass) 26- 61 Figure 26.6 Figure Representative Monoterpenes α-Phellandrene Menthol (eucalyptus) (peppermint) Dr. Wolf's CHM 424 Citral (lemon grass) 26- 62 Figure 26.6 Representative Sesquiterpenes H α-Selinene (celery) Dr. Wolf's CHM 424 26- 63 Figure 26.6 Representative Sesquiterpenes H α-Selinene (celery) Dr. Wolf's CHM 424 26- 64 Figure 26.6 Figure Representative Sesquiterpenes α-Selinene (celery) Dr. Wolf's CHM 424 26- 65 Figure 26.6 Representative Diterpenes OH OH Vitamin A Dr. Wolf's CHM 424 26- 66 Figure 26.6 Representative Diterpenes OH OH Vitamin A Dr. Wolf's CHM 424 26- 67 Figure 26.6 Representative Diterpenes Vitamin A Dr. Wolf's CHM 424 26- 68 Figure 26.6 Representative Triterpene tail-to-tail linkage of isoprene units tail-to-tail Dr. Wolf's CHM 424 Squalene (shark liver oil) 26- 69 26.8 Isopentenyl Pyrophosphate: The Biological Isoprene Unit Dr. Wolf's CHM 424 26- 70 The Biological Isoprene Unit The isoprene units in terpenes do not come from The isoprene. isoprene. They come from isopentenyl pyrophosphate. Isopentenyl pyrophosphate (5 carbons) comes Isopentenyl from acetate (2 carbons) via mevalonate (6 carbons). carbons). Dr. Wolf's CHM 424 26- 71 The Biological Isoprene Unit O O 3 CH3COH CH3 HOCCH2CCH2CH2OH OH CH3 H2C Mevalonic acid OO CCH2CH2OPOPOH Isopentenyl pyrophosphate Isopentenyl pyrophosphate Dr. Wolf's CHM 424 26- 72 Isopentenyl Pyrophosphate CH3 H2C OO CCH2CH2OPOPOH or OPP OPP Isopentenyl pyrophosphate Isopentenyl pyrophosphate Dr. Wolf's CHM 424 26- 73 Isopentenyl and Dimethylallyl Pyrophosphate Isopentenyl pyrophosphate is interconvertible with 2-methylallyl pyrophosphate. OPP OPP Isopentenyl pyrophosphate OPP OPP Dimethylallyl pyrophosphate Dimethylallyl pyrophosphate has a leaving Dimethylallyl group (pyrophosphate) at an allylic carbon; it is reactive toward nucleophilic substitution at this position. position. Dr. Wolf's CHM 424 26- 74 26.9 Carbon-Carbon Bond Formation Carbon-Carbon in Terpene Biosynthesis in Dr. Wolf's CHM 424 26- 75 Carbon-Carbon Bond Formation OPP OPP + OPP The key process involves the double bond of The isopentenyl pyrophosphate acting as a nucleophile pyrophosphate toward the allylic carbon of dimethylallyl pyrophosphate. pyrophosphate Dr. Wolf's CHM 424 26- 76 Carbon-Carbon Bond Formation OPP OPP + OPP – OPP + Dr. Wolf's CHM 424 OPP 26- 77 After C—C Bond Formation... OPP OPP The carbocation The can lose a proton to give a double bond. bond. + –H + Dr. Wolf's CHM 424 OPP 26- 78 After C—C Bond Formation... OPP OPP This compound is called geranyl pyrophosphate. It This can undergo hydrolysis of its pyrophosphate to give geraniol (rose oil). geraniol Dr. Wolf's CHM 424 26- 79 After C—C Bond Formation... OPP OPP H2O OH OH Dr. Wolf's CHM 424 Geraniol 26- 80 From 10 Carbons to 15 OPP OPP + OPP Geranyl pyrophosphate Geranyl + Dr. Wolf's CHM 424 OPP 26- 81 From 10 Carbons to 15 OPP OPP + –H + Dr. Wolf's CHM 424 OPP 26- 82 From 10 Carbons to 15 OPP OPP This compound is called farnesyl This pyrophosphate. pyrophosphate. Hydrolysis of the pyrophosphate ester gives the Hydrolysis alcohol farnesol (Figure 26.6). alcohol Dr. Wolf's CHM 424 26- 83 From 15 Carbons to 20 OPP OPP OPP OPP Farnesyl pyrophosphate is extended by another Farnesyl isoprene unit by reaction with isopentenyl pyrophosphate. pyrophosphate. Dr. Wolf's CHM 424 26- 84 Cyclization Rings form by intramolecular carbon-carbon Rings bond formation. bond + OPP OPP OPP OPP E double bond bond Dr. Wolf's CHM 424 Z double bond bond 26- 85 Limonene + –H + OH OH H2O α-Terpineol Dr. Wolf's CHM 424 26- 86 Bicyclic Terpenes + + + + α-Pinene Dr. Wolf's CHM 424 β-Pinene 26- 87 26.10 The Pathway from Acetate to The Isopentenyl Pyrophosphate Isopentenyl Dr. Wolf's CHM 424 26- 88 Recall O O 3 CH3COH CH3 HOCCH2CCH2CH2OH OH CH3 H2C Mevalonic acid OO CCH2CH2OPOPOH Isopentenyl pyrophosphate Isopentenyl pyrophosphate Dr. Wolf's CHM 424 26- 89 Biosynthesis of Mevalonic Acid In a sequence analogous to the early steps of In fatty acid biosynthesis, acetyl coenzyme A is converted to S-acetoacetyl coenzyme A. O O CH3CCH2CSCoA S-Acetoacetyl coenzyme A Dr. Wolf's CHM 424 26- 90 Biosynthesis of Mevalonic Acid O O O CH3CCH2CSCoA + CH3CSCoA In the next step, S-acetoacetyl coenzyme A In reacts with acetyl coenzyme A. reacts Nucleophilic addition of acetyl coenzyme A Nucleophilic (probably via its enol) to the ketone carbonyl of S-acetoacetyl coenzyme A occurs. S- Dr. Wolf's CHM 424 26- 91 Biosynthesis of Mevalonic Acid O O O CH3CCH2CSCoA + CH3CSCoA HO O CH3CCH2CSCoA CH2COH Dr. Wolf's CHM 424 O 26- 92 Biosynthesis of Mevalonic Acid Next, the acyl coenzyme A function is reduced. Next, function The product of this reduction is mevalonic acid. HO O CH3CCH2CSCoA CH2COH Dr. Wolf's CHM 424 O 26- 93 HO CH3CCH2CH2OH CH2COH Mevalonic acid O HO O CH3CCH2CSCoA CH2COH Dr. Wolf's CHM 424 O 26- 94 Conversion of Mevalonic Acid to Conversion Isopentenyl Pyrophosphate Isopentenyl 2– HO OPO3 CH3CCH2CH2OH CH3CCH2CH2OPP CH2COH CH2COH O O The two hydroxyl groups of mevalonic acid The undergo phosphorylation. undergo Dr. Wolf's CHM 424 26- 95 Conversion of Mevalonic Acid to Conversion Isopentenyl Pyrophosphate Isopentenyl 3– 2– OPO3 OPO3 CH3CCH2CH2OPP CH CH2 O CH3CCH2CH2OPP CH2 C O C •• • – O• •• O Phosphorylation is followed by a novel Phosphorylation elimination involving loss of CO2 and PO43–. elimination Dr. Wolf's CHM 424 26- 96 Conversion of Mevalonic Acid to Conversion Isopentenyl Pyrophosphate Isopentenyl CH3CCH2CH2OPP CH2 The product of this elimination is isopentenyl The pyrophosphate. pyrophosphate. Dr. Wolf's CHM 424 26- 97 Biosynthetic pathway is based on Biosynthetic 14 experiments with 14C-labeled acetate O O CH3COH CH3 HOCCH2CCH2CH2OH OH CH3 H2C Mevalonic acid OO CCH2CH2OPOPOH Isopentenyl pyrophosphate Isopentenyl pyrophosphate Dr. Wolf's CHM 424 26- 98 Biosynthetic pathway is based on Biosynthetic 14 experiments with 14C-labeled acetate 14 Citronellal biosynthesized using 14C-labeled Citronellal C-labeled acetate as the carbon source had the labeled carbons in the positions indicated. carbons CH3 O CH3COH H2C • • • • Dr. Wolf's CHM 424 • OO CCH2CH2OPOPOH O • H 26- 99 26.11 Steroids: Cholesterol Dr. Wolf's CHM 424 26- 100 Structure of Cholesterol Fundamental framework of steroids is the tetracyclic unit shown. tetracyclic Dr. Wolf's CHM 424 26- 101 Structure of Cholesterol CH3 CH3 CH3 H CH3 CH3 H H HO HO Cholesterol has the fundamental steroid Cholesterol skeleton modified as shown. skeleton Dr. Wolf's CHM 424 26- 102 Structure of Cholesterol Structure CH3 CH3 CH3 H CH3 CH3 H H HO Some parts of the cholesterol molecule are Some isoprenoid. But other parts don't obey the isoprene rule. Also, cholesterol has 27 carbons, which is not a multiple of 5. which Dr. Wolf's CHM 424 26- 103 Biosynthesis of Cholesterol Cholesterol is biosynthesized from the triterpene Cholesterol squalene. In the first step, squalene is converted to its 2,3-epoxide. converted O2, NADH, enzyme O Dr. Wolf's CHM 424 26- 104 Biosynthesis of Cholesterol O To understand the second step, we need to look To at squalene oxide in a different conformation, one that is in a geometry suitable for cyclization. one O Dr. Wolf's CHM 424 26- 105 Biosynthesis of Cholesterol HO + H Cyclization is triggered by epoxide ring opening. H+ O Dr. Wolf's CHM 424 26- 106 Biosynthesis of Cholesterol HO + H The five-membered ring expands to a six-membered The one. one. H HO + H Dr. Wolf's CHM 424 26- 107 Biosynthesis of Cholesterol H + HO protosteryl cation H Cyclization to form a tetracyclic carbocation. H HO + H Dr. Wolf's CHM 424 26- 108 Biosynthesis of Cholesterol •• • • OH2 H + HO H H Deprotonation and multiple migrations. H HO HO H Dr. Wolf's CHM 424 26- 109 Biosynthesis of Cholesterol The product of this rearrangement is a triterpene The called lanosterol. A number of enzymecalled catalyzed steps follow that convert lanosterol to catalyzed cholesterol. cholesterol. H HO HO H Dr. Wolf's CHM 424 26- 110 Cholesterol Cholesterol is the biosynthetic precursor to a Cholesterol large number of important steroids: large Bile acids Vitamin D Corticosteroids Sex hormones Dr. Wolf's CHM 424 26- 111 26.12 Vitamin D Dr. Wolf's CHM 424 26- 112 Cholesterol CH3 CH3 CH3 H CH3 CH3 H H HO HO Cholesterol is the precursor to vitamin D. Enzymes dehydrogenate cholesterol to introduce a second Enzymes double bond in conjugation with the existing one. The product of this reaction is called 7-dehydrocholesterol. product Dr. Wolf's CHM 424 26- 113 7-Dehydrocholesterol 7-Dehydrocholesterol CH3 CH3 CH3 CH3 H CH3 H HO Sunlight converts 7-dehydrocholesterol on the Sunlight skin's surface to vitamin D3. skin's Dr. Wolf's CHM 424 26- 114 Vitamin D3 CH3 CH3 CH3 CH3 H HO HO Insufficient sunlight can lead to a deficiency of Insufficient vitamin D3, interfering with Ca2+ transport and vitamin bone development. Rickets can result. bone Dr. Wolf's CHM 424 26- 115 26.13 Bile Acids Dr. Wolf's CHM 424 26- 116 Cholesterol CH3 CH3 CH3 H CH3 CH3 H H HO HO Oxidation in the liver degrades the cholesterol side chain Oxidation and introduces OH groups at various positions on the steroid skeleton. Cholic acid (next slide) is the most abundant of the bile acids. abundant Dr. Wolf's CHM 424 26- 117 Cholic Acid O HO CH3 CH3 CH3 H HO OH H H OH H Salts of cholic acid amides (bile salts), such as sodium ), taurocholate (next slide), act as emulsifying agents to aid digestion. Dr. Wolf's CHM 424 26- 118 Sodium Taurocholate O HO CH3 CH3 CH3 H HO NHCH2CH2SO3Na H H OH H Dr. Wolf's CHM 424 26- 119 26.14 Corticosteroids Dr. Wolf's CHM 424 26- 120 Cholesterol CH3 CH3 CH3 H CH3 CH3 H H HO HO Enzymatic degradation of the side chain and oxidation of Enzymatic various positions on the steroid skeleton convert cholesterol to corticosteroids. corticosteroids Dr. Wolf's CHM 424 26- 121 Cortisol Cortisol HO CH3 H O CH3 OH OH H H O Cortisol is the most abundant of the corticosteroids. Cortisol Enzyme-catalyzed oxidation of cortisol gives cortisone. Enzyme-catalyzed Dr. Wolf's CHM 424 26- 122 Cortisone O CH3 O CH3 H OH OH H H O Corticosteroids are involved in maintaining electrolyte Corticosteroids levels, in the metabolism of carbohydrates, and in mediating the allergic response. mediating Dr. Wolf's CHM 424 26- 123 26.15 Sex Hormones Dr. Wolf's CHM 424 26- 124 Testosterone H3C H3C OH H H H O Testosterone is the main male sex hormone. Testosterone Dr. Wolf's CHM 424 26- 125 Estradiol Estradiol H3C OH H H H HO HO Estradiol is a female sex hormone involved in Estradiol regulating the menstrual cycle and in reproduction. Dr. Wolf's CHM 424 26- 126 Progesterone O H3C H3C H H H O Supresses ovulation during pregnancy. Supresses Dr. Wolf's CHM 424 26- 127 26.16 Carotenoids Dr. Wolf's CHM 424 26- 128 Carotenoids Carotenoids are naturally occurring pigments. Structurally, carotenoids are tetraterpenes. Structurally, They have 40 carbons. Two C20 units are linked They in a tail-to-tail fashion. in Examples are lycopene and β-carotene. Examples Dr. Wolf's CHM 424 26- 129 Carotenoids Lycopene (tomatoes) β-Carotene (carrots) Dr. Wolf's CHM 424 26- 130 End of Chapter 26 Dr. Wolf's CHM 424 26- 131 ...
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This document was uploaded on 01/03/2012.

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