Chapter 27. Biomolecules: Lipids Based on McMurry’s Organic Chemistry, 6th...

download Chapter 27. Biomolecules: Lipids Based on McMurry’s Organic Chemistry, 6th edition

of 38

  • date post

    26-Dec-2015
  • Category

    Documents

  • view

    233
  • download

    3

Embed Size (px)

Transcript of Chapter 27. Biomolecules: Lipids Based on McMurry’s Organic Chemistry, 6th...

  • Slide 1
  • Chapter 27. Biomolecules: Lipids Based on McMurrys Organic Chemistry, 6th edition
  • Slide 2
  • About Lipids Naturally materials that preferentially extract into nonpolar organic solvents Includes fats, oils, waxes, some vitamins and hormones, some components of membrane General types: esters (saponifiable) and those that cant be hydrolyzed
  • Slide 3
  • 27.1 Waxes, Fats, and Oils Waxes - contain esters formed from long-chain (C16- C36) carboxylic acids and long-chain alcohols (C24- C36) Triacontyl hexadecanoate is in beeswax
  • Slide 4
  • Fats and Oils Animal fats and vegetable are triacylglycerols oil Triesters of glycerol with three long-chain carboxylic acids Saponification of a fat or oil with (reaction with aqueous NaOH) yields glycerol and three fatty acids
  • Slide 5
  • Fatty Acids (from Fats and Oils) Straight-chain (C 12 - C 20 ) carboxylic acids Double bonds are cis-substituted but trans-fatty acid also occur A fat or oil in nature occurs as a mixture of many different triacylglycerols The most abundant saturated fatty acids are palmitic (C 16 ) and stearic (C 18 )
  • Slide 6
  • Unsaturated and Polyunsaturated Fatty Acids Oleic (C 18 with one C=C) and linolenic (C 18 with 3 C=C) are the most abundant unsaturated
  • Slide 7
  • 27.2 Soap A mixture of sodium or potassium salts of long-chain fatty acids produced by alkaline hydrolysis (saponification) of animal fat with alkali
  • Slide 8
  • Cleansing Action of Soap The carboxylate end of the long-chain molecule is ionic and therefore is preferentially dissolved in water The hydrocarbon tail is nonpolar and dissolves in grease and oil Soaps enable grease to be dissolved into water
  • Slide 9
  • Detergents Hard water contains Mg +2 and Ca +2 that form insoluble salts with soaps Synthetic detergents are alkylbenzene sulfonates that dissolve dirt like soaps but do not form scums with Mg +2 and Ca +2.
  • Slide 10
  • 27.3 Phospholipids Phospholipids are diesters of H 3 PO 4, phosphoric acid Phosphoric acid can form monoesters, diesters and triesters In general these are known as phosphates
  • Slide 11
  • Phosphoglycerides Contain a glycerol backbone linked by ester bonds to two fatty acids and phosphoric acid Fatty acid residues with C 12 C 20 The phosphate group at C3 has an ester link to an amino alcohol
  • Slide 12
  • Phosphoglyceride Membranes Phosphoglycerides comprise the major lipid component of cell membranes Nonpolar tails aggregate in the center of a bilayer Ionic head is exposed to solvent
  • Slide 13
  • Sphingolipids The other major group of phospholipids Sphingosine or a dihydroxyamine backbone Constituents of plant and animal cell membranes Abundant in brain and nerve tissue, as coating around nerve fibers.
  • Slide 14
  • 27.4 Prostaglandins C20 lipids that contain a five-membered ring with two long side chains Present in small amounts in all body tissues and fluids Many physiological effects
  • Slide 15
  • Prostaglandin Sources Biosynthesized from arachidonic acid (C20 unsaturated fatty acid) Catalyzed by cyclooxygenase (COX)
  • Slide 16
  • 27.5 Terpenoids Steam distillation of plant extracts produces essential oils Chemically related to compounds in turpentine (from pine sap) called terpenes and thus called terpenoids Mostly hydrocarbons (some oxygens) that do not contain esters (stable to hydrolysis)
  • Slide 17
  • Terpenoids Are Isoprenoids Terpenoid structures are derived from isoprene (2- methyl-1,3-butadiene) units connected head-to-tail (Isoprene Rule) The term head-to-tail means that dissimilar ends are connected (you can choose which is a head and which is a tail)
  • Slide 18
  • Classification of Terpenoids Classified according to the number of di-isoprenoid (C 10 ) units they contain Monoterpenes have 10-carbons, sesquiterpenes (sesqui = 1 1/2) have 15-carbons from three isoprene units, and so on
  • Slide 19
  • Some Important Terpenoids The triterpene lanosterol is the precursor of steroid hormones The tetraterpene -carotene is a source of vitamin A
  • Slide 20
  • 27.6 Biosynthesis of Terpenoids Isopentenyl pyrophosphate (IPP) forms higher isoprenoids in reactions catalyzed by prenyl transferase Monoterpenoids, diterpenoids, and tetraterpoids arise from 1-deoxyxylulose 5-phosphate.
  • Slide 21
  • Mevalonate Pathway to Isopentenyl Diphosphate Begins with the conversion of acetate to acetyl CoA followed by Claisen condensation to yield acetoacetyl CoA Catalyzed by acetoacetyl-CoA acetyltransferase
  • Slide 22
  • Aldol Condensation Produces HMG-CoA Carbonyl condensation reaction of acetoacetyl CoA with acetyl CoA Produces 3-hydroxy-3-methylglutaryl CoA (HMG-CoA)
  • Slide 23
  • Reduction Forms Mevalonate HMG CoA is reduced to mevalonate Catalyzed by HMG CoA reductase utilizing NADPH
  • Slide 24
  • Conversion of Mevalonate to IPP Pyrophosphorylation gives mevalonyl-PP Addition of phosphate from ATP followed by loss of CO 2 and phosphate
  • Slide 25
  • Conversion of Isopentenyl Diphosphate to Terpenoids For triterpenes and larger, head-to-head coupling of farnesyl diphosphates gives squalene
  • Slide 26
  • Mechanism of Isomerization Isomerization of IPP to DMAPP is catalyzed by IPP isomerase through a carbocation pathway
  • Slide 27
  • Coupling Mechanism Nucleophilic substitution reaction in which the double bond of IPP behaves as a nucleophile in displacing diphosphate ion leaving group (PPO )
  • Slide 28
  • Conversions of Monoterpenoids Typically involves carbocation intermediates and multistep reaction pathways catalyzed by a terpene cyclase
  • Slide 29
  • 27.7 Steroids Steroids,are another class of nonsaponifiable lipid, defined by structure Has four fused rings A, B, C, and D, beginning at the lower left Carbon atoms are numbered beginning in the A ring The six-membered rings are in fixed chair conformations
  • Slide 30
  • Functions of Steroids In humans as hormones, steroids are chemical messengers secreted by glands and carried through the bloodstream to target tissues Also widely distributed as cholesterol
  • Slide 31
  • Male Sex Hormones Testosterone and androsterone are the two most important male sex hormones, or androgens Androstanedione is a precursor
  • Slide 32
  • Female Sex Hormones Estrone and estradiol are the two most important female sex hormones, or estrogens Progesterone is the most important progestin, steroids that function in pregnancy
  • Slide 33
  • Adrenocortical Hormones Adrenocortical steroids: secreted by the adrenal glands near the upper end of each kidney Mineralocorticoids: control tissue swelling by regulating cellular salt balance Glucocorticoids: regulation of glucose metabolism and in the control of inflammation
  • Slide 34
  • Synthetic Steroids Made in pharmaceutical laboratories as new drugs Includes oral contraceptives and anabolic agents Methandrostenolone is an anabolic steroid used for tissue-building
  • Slide 35
  • 27.8 Stereochemistry of Steroids Two cyclohexane rings can be joined in either a cis or a trans manner In cis-decalin, both groups at the ring-junction positions are on the same side of the two rings In trans-decalin, the groups at the ring junctions are on opposite sides
  • Slide 36
  • A/B Junction in Steroids Steroids can have either a cis or a trans fusion of the A and B ring (BC and CD) are usually trans
  • Slide 37
  • 27.9 Steroid Biosynthesis Enzyme-catalyzed addition of oxygen atom to squalene Stereospecific formation of an oxirane from an alkene
  • Slide 38
  • Cyclization to Steroid Stork-Eschenmoser mechanism Enzyme-catalyzed See Figure 27.6