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Lipid

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  • 1. Biochemistry of Lipid & Membranes Introduction to Lipid Dr. Yogesh V. Ushir 16-07-2012 1
  • 2. What are lipids? Lipids are chemically diverse groups of compounds, the common and defining feature of which is their insolubility in water Lipids are extracted from tissues with organic solvents such as ethyl ether, chloroform, and acetone. Lipids are condensational product of alcohol and fatty acids and their derivatives 16-07-2012 2
  • 3. Fatty acids Fatty acids are carboxylic acids with hydrocarbon chains ranging from 4-36 carbons long. In some fatty acids, this chain is unbranched and fully saturated In others, the chains can contain one or more double bonds A few fatty acids contain 3 carbon rings, hydroxyl group, or methyl groups branches 16-07-2012 3
  • 4. Nomenclature of fatty acids Number of double bond Position of double bond Carbon chain length 18:3 (Δ 9, 12, 15 ) The most commonly occurring fatty acids have even number of carbon atoms in an unbrached chain of 12-24 carbons 16-07-2012 4
  • 5. Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents. Most membrane lipids are amphipathic, having a non-polar end and a polar end. Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end. A 16-C fatty acid: CH3(CH2)14-COONon-polar polar A 16-C fatty acid with one cis double bond between C atoms 9-10 may be represented as 16:1 cis ∆ 9. 16-07-2012 5
  • 6. General pattern of double bonds The most common position for double bonds are Δ9, Δ12, and Δ15 The double bonds of poly saturated fatty acids are separated by methyl group: -CH=CH-CH2-CH=CHIn almost all naturally occurring unsaturated fatty acids, the double bonds are cis configuration. eg. N-dodecanoic acid, n-eicosanoic acid (in Arachis oil) 16-07-2012 6
  • 7. O β Double bonds in fatty γ α C − 3 acids usually have the 1 O 4 2 cis configuration. Most naturally fatty acid with a cis-∆9 occurring fatty acids double bond have an even number of carbon atoms. Some fatty acids and their common names: 14:0 myristic acid; 16:0 palmitic acid; 18:0 stearic acid; 18:1 cis∆9 oleic acid 18:2 cis∆9,12 linoleic acid 18:3 cis∆9,12,15 α-linonenic acid 20:4 cis∆5,8,11,14 arachidonic acid 20:5 cis∆5,8,11,14,17 eicosapentaenoic acid (an omega-3) 16-07-2012 7
  • 8. γ 4 β 3 α 2 O C 1 O− fatty acid with a cis-∆9 double bond There is free rotation about C-C bonds in the fatty acid hydrocarbon, except where there is a double bond. Each cis double bond causes a kink in the chain. Rotation about other C-C bonds would permit a more linear structure than shown, but there would be a kink. 16-07-2012 8
  • 9. Classification of fatty acids Saturated Unsaturated 16-07-2012 9
  • 10. Saturated fatty acids Represented by general formula CH3(CH2)nCOOH The simplest is the acetic acid where n=0 Does not show double bond in structure 16-07-2012 10
  • 11. Some of saturated fatty acids Saturated fatty acid formula Acetic acid CH3COOH 0 Butyric acid CH3(CH2)2COOH 4 Caproic acid CH3(CH2)4COOH 6 Lauric acid CH3(CH2)10COOH 12 Myritic acid CH3(CH2)12COOH 14 Palmitic acid CH3(CH2)14COOH 16 Stearic acid CH3(CH2)16COOH 18 Arachidic acid CH3(CH2)18COOH 20 Lignoceric acid CH3(CH2)22COOH 24 16-07-2012 Number of C-atom 11
  • 12. UnSaturated fatty acids They contain one or more double bonds Some of them are:  Palmitoleic acid  Oleic acid  Linoleic acid  Arachidonic acid  Cyclic fatty acids  Prostaglandins 16-07-2012 12
  • 13. Physical properties of Fatty acids The physical properties of fatty acids are largely determined by the length and degree of unsaturation of the hydrocarbon chain The longer the chain and fewer the double bonds, the lower is the solubility in water, and higher the melting point The lower fatty acid are liquid and higher fatty acids are solid at room temperature Most of the fatty acids lighter than water 16-07-2012 13
  • 14. Chemical properties of Fatty acids Formation of esters with alcohols Formation of soaps with alkalies RCOOH + NaOH ---------------- RCOONa + H2O Detergents Due to double bond of unsaturated fatty acids Hydrogenation Halogenation Oxidation at double bond 16-07-2012 14
  • 15. Classification of Lipids Based on their biological functions, lipids can be classified into: Storage Lipid --- Principle stored form of energy Structural Lipids --- The major structural elements of biological membranes Lipids as signals, cofactors, and pigments 16-07-2012 15
  • 16. Storage Lipids Storage lipids include fats and oils, and wax Fats & oils are composed of three fatty acids each in ester linkage with a single glycerol (Triglycerols) Waxes are ester of long-chain (C14-C36) saturated and unsaturated fatty acids with long-chain (C16C30) alcohols 16-07-2012 16
  • 17. Lipid as Structural Elements Membrane Lipids Phospholipids Glycerophospholipids Spingolipids Glycolipids Spingolipids Galactolipids/Sulpholipids Archaebacterial ether lipids Sterols 16-07-2012 17
  • 18. Lipids as Signals, Cofactors, and Pigments Some lipids, presents in very small amount, have active role in the metabolic traffic as metabolites & messengers. They serve the following functions: As signal molecules As enzyme cofactors As pigments 16-07-2012 18
  • 19. Based on their chemical structure, lipids can be classified into: Simple Lipid --- Esters of fatty acids with alcohol  Fats & oils  waxes Complex Lipids --- esters of fatty acids with alcohols containing additional groups as, Po4, nitrogenous bases, carbohydrates, proteins etc  Phospholipids  Glycerophospholipids  Glycolipids  Sphingophospholipids  Lipoproteins  Sulpholipids, 16-07-2012 aminolipids, 19
  • 20. Derived Lipids  Lipid (fat) soluble vitamins  Steroid hormones  Ketone bodies Miscellaneous Lipids  Carotenoids  Squalene  Terpenes NEUTRAL LIPIDS  triglycerides 16-07-2012 20
  • 21. Simple Lipids A. Fats & oils :  These are fatty acids esters of the trihydric alcohol, glycerol.  Are also known as triglycerides or triacylglycerols (TAG)  Glycerols + Fatty Acids ------------- TAG  Most of occurring TAG’s are mixed, which contain 2 or more different fatty acids. TAGs are nonpolar, hydrophobic molecules, essentially insoluble in water 16-07-2012 21
  • 22. Identification of Fats & Oils Hydrolysis Acetyl number Saponification Polenske number Saponification Reichert-Miessl number Acid number Iodine number 16-07-2012 number Halogenation Rancidity 22
  • 23. B. Waxes Waxes are ester of long-chain (C14-C36) saturated and unsaturated fatty acids with long-chain (C16C30) alcohols. In human body commonest waxes are esters of cholesterol Three types are; True waxes- esters of higher fatty acids with acetyl 16-07-2012 alcohol or other higher straight chain alcohols Cholesterol esters - are esters of fatty acids with cholesterol Vit. A & D esters- are palmitic acid or stearic acid esters of vitamin A (Retinol) or vitamin D, respectively 23
  • 24. Functions of Wax Chief storage fuels for some microorganisms Protect skin and hair Prevent excess water evaporation in plants Protect against parasites Application in industries, pharmaceuticals, and Cosmetics 16-07-2012 24
  • 25. Example BEES WAX- palmitic acid ester of myricyl alcohol (C30H61OH) LANOLIN or WOOL FAT- palmitic, oileic or steric acid ester of cholesterol SPERMACETI- palmitic acid ester of cetyl alcohol (C16H33OH). It is oil from head of whale 16-07-2012 25
  • 26. Compound lipids Most of complex lipids have structural function in cell membrane Glycero-phospholipids Phospholipids Sphingo-lipids Membrane Glyco-lipids Galacto-lipids/Sulfolipids 16-07-2012 26
  • 27. STRCTURE OF CELL MEMBRANE 16-07-2012 27
  • 28. A. Phospholipids (phosphatides)  Are esters of fatty acids with glycerol containing an esterified phosphoric acid and an nitrogen base  They are present in large amount in Nervous tissue, brain, liver, kidney, pancrease, and heart 16-07-2012 28
  • 29. Functions of Phospholipids They increases the rate of fatty acid oxidation They act as carriers of inorganic ions across the membranes They helps blood clotting They acts as prosthetic group for certain enzymes They forms the structures of membranes, matrix of cell wall, myelin sheath, microsomes and mitochondria 16-07-2012 29
  • 30. Phospholipids (Continu…) These are lipids that contain one or more phosphate groups PL are the primary components of biomembranes. Other lipids in biomembranes are glycolipids and cholesterol. Surfactants are phopsholipids, mostly phosphatidylcholine  PL are subclassifiedbased on their parent lipid; phopshoglycerides or sphingomyelins 16-07-2012 30
  • 31. PL are subclassifiedbased on their alcohol present in the phospholipid Glycerophosphatides- glycerol is alcohol gr.  phosphatidylserine; phosphatidylcholine (Lecithins); phosphatidy lethanolamine (Cephalin); Diphosphatidylglycerol(cardiolipin) Phosphoinositides- inisitol is alcohol gr.  phosphatidylinositol; Phosphospingosides- sphingosine is an amino alcohol  16-07-2012 Sphingomyelins; 31
  • 32. Glycerophospholipids Are Derivatives of Phosphatidic Acid Glycerophospholipidis named for the head group with the prefix “phosphatidyl-.” 16-07-2012 32
  • 33. Glycerophospholipids 16-07-2012 33
  • 34. Di-Phosphotidyl glycerol It is important intermediate form in the synthesis of TAG’s and PL Another name is Cardiolipin Form from Phosphotidyl glycerol  Chemically di Phosphotidyl glycerol  Present in inner membrane of bacterial wall and mitochondria  16-07-2012 34
  • 35. Phosphatidylcholine Lecithins Contains glycerols and saturated fatty acids, phosphoric acid and choline (N-base) 16-07-2012 35
  • 36. Spingolipids 16-07-2012 36
  • 37. Sphingosine is a derivative of glycerol but it has – NH2 instead of -OH at C2 and has a -OH as well as a long chain hydrocarbon on C3 The –NH2 forms an amide bond with a long chain FA to form a ceramide. Sphigomyelin is formed when a phosphodiester bridge links the C1 -OH of ceramide to ethanolamine or choline 16-07-2012 37
  • 38. Spingomyelins Found large quantities in brain & nervous tissue The concentration of this PL are increased in liver and Spleen; due to metabolic defect called NiemannPick’s Disease Consist sphingol (complex amino alcohol), fatty acids, choline and phosphoric acid No glycerol is present Sphingomyelins are present in the plasma membrane of animal cells, especially in myelin, a membrane sheath that insulate the axons of some neurons 16-07-2012 38
  • 39. B. Glycolipids  Contain an amino acid alcohol (Spingosine or iso- spingosine) attached with an amide linkage to a fatty acids and glycosidically to a carbohydrate moiety  Glycolipids are lipids that contain carbohydrates  Two types   16-07-2012 Cerebrosides Gangliosides 39
  • 40.  Cerebrosides have a monosaccharide attached to the C1 -OH of ceramide Gangliosides have an oligosaccharide attached to theC1 -OH of ceramide Cerebrosides are found in the brain and Spinal Chord. Chief constituent of myelin sheath Gangliosides are found in the ganglions of brain In biomembranes, glycolipids are oriented asymmetrically with the sugar units always on the extracellular side of the membrane 16-07-2012 40
  • 41. Other compound lipids Lipoproteins TAG’s (45%) + PL (35%) + Cholesterols + Cholesterly esters (15%) + FFA (< 5%) and also protein combine to form a hydrophillic lipoprotein complex 4 major gr of LP are identified which are important physiologically & in clinical diagnostic in some metabolic disorders; Chylomicrons  VLDL (pre- β-LP)  LDL (β-LP)  HDL (α-LP)  16-07-2012 41
  • 42. Aminolipids Phophatidyl ethanolamine & serine are aminolipids Sulpholipids Sulphatides Isolated from brain and other animal tissues  Sulfolipids have a sulfonated glucose residue joined to a diacylglycerol in glycosidic linkage.  Theyalso exist predominantly in chloroplasts. 16-07-2012 42
  • 43. Derived lipids The derived from the simple lipid & compound lipid hence the name given. 16-07-2012 43
  • 44. Steroids Sterols: Cholesterol, Ergosterol, coprosterol Bile acids : Glycocholic acid, taurocholic acid Sex harmones: testosterone, estradiol Adrenal cortical hormones: corticosterone Vit. D: Vit. D2 & D3 Cardiac glycosides: strophanthin Saponins: Digitonin Are the some important derived lipids 16-07-2012 44
  • 45. Chemical reactions for derived lipids Salkowski reaction  Sterol gives red color at the bottom of the test tube when treated with conc. Sulphuric acid Lieberman-Burchard reaction  16-07-2012 Sterol gives rose-red color when chloroform layer treated with acetic anhydride & conc. Sulphuric acid, which rapidely changes to blue & finally green 45
  • 46. Cholesterol One of the important derived lipid Meaning solid alcohol from bile Sources- diet: only found in animal fat brain, nervous tissues, adrenal glands & egg yolk are rich sources 16-07-2012 46
  • 47. biosynthesis and degradation biosynthesis: primarily synthesized in the liver from acetyl-coA; biosynthesis is inhibited by LDL uptake degradation: only occurs in the liver 16-07-2012 47
  • 48. Properties of cholesterol The double bond can be saturated by addition of hydrogen to form the dihydroderivative, it can also be halogenated The 3 position OH group can be esterified with fatty acids to form cholesterol esters; three fourths of cholesterol of plasma exists as ester Lanoline the cholesterol ester already studies as under WAXES 16-07-2012 48
  • 49. H3 C CH3 H CH3 hydrophobic O H OH H drawn this way R O usually palmitate hydrophillic 16-07-2012 49
  • 50. Cholesterol and cholesterol esters H H HO Functions: -serves as a component of membranes of cells (increases or moderates membrane fluidity -precursor to steroid hormones -storage and transport – cholesterol esters 16-07-2012 50
  • 51. STEROID NUMBERING SYSTEM 18 12 1 2 A 3 4 16-07-2012 C 13 11 19 17 D 14 9 10 B 8 16 15 7 5 6 51
  • 52. Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail. HO Cholesterol is largely hydrophobic. Cholesterol cholesterol But it has one polar group, a hydroxyl, making it amphipathic. 16-07-2012 52
  • 53. HO Cholesterol Cholesterol in membrane Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids. The OH group of cholesterol forms hydrogen bonds with polar phospholipid head groups. 16-07-2012 53
  • 54. Interaction with the relatively rigid cholesterol decreases the mobility of hydrocarbon tails of phospholipids. But the presence of cholesterol in a phospholipid membrane interferes with close packing of fatty acid tails in the crystalline state, and thus inhibits transition to the crystal state. Phospholipid membranes with a high concentration of cholesterol have a fluidity intermediate between the liquid crystal and crystal states. 16-07-2012 54
  • 55. Functions of cholesterol serves as a component of membranes of Cholesterol in membrane cells (increases or moderates membrane fluidity) precursor to steroid hormones and bile acids storage and transport –cholesterol esters 16-07-2012 55
  • 56. 16-07-2012 56
  • 57. Photograph of an arterial plaque 16-07-2012 57
  • 58. Prostaglandins and other eicosanoids (prostanoids) local hormones, unstable, key mediators of inflammation derivatives of prostanoic acid 9 8 COOH 20 11 12 15 prostanoic acid 16-07-2012 58
  • 59. O O O R O OO O P X H20 phospholipase A2 (enzyme that hydrolyzes at the sn-2 position - inhibited indirectly by corticosteroids) O COOH CH3 COX is inhibibited by aspirin and other NSAIDs very unstable bond prostaglandin synthase (also known as cyclooxygenase) O COOH O 16-07-2012 PGH2 OH 59
  • 60. O COOH O OH PGH2 O HO COOH COOH HO OH PGE2 key mediator of inflammation 16-07-2012 HO OH PGF2α 60
  • 61. O O O HO R1 R1 R1 R1 R2 R2 R2 R2 PGB PGA O R1 O PGC HO R1 R1 R1 O PGD O R2 HO R2 O R2 HO PGE PGG and PGH PGFa R2 HO PGI R1 OH O R1 R1 R1 O R2 O PGJ R2 O R2 HO O R2 O PGK TXA TXB SUBSTITUTION PATTERN OF PROSTANOIDS 16-07-2012 61
  • 62. Prostacyclins, thromboxanes and leukotrienes PGH2 in platelets is converted to thromboxane A2 (TXA2) a vasoconstrictor which also promotes platelet aggregation PGH2 in vascular endothelial cells is converted to PGI2, a vasodilator which inhibits platelet aggregation Aspirin’s irreversible inhibition of platelet COX leads to its anticoagulant effect 16-07-2012 62
  • 63. Functions of eicosanoids Prostaglandins – particularly PGE1 – block gastric production and thus are gastric protection agents Misoprostol (Cytotec) is a stable PGE1 analog that is used to prevent ulceration by long term NSAID treatment PGE1 also has vasodilator effects Alprostadil (PGE1) – used to treat infants with congenital heart defects Also used in impotance (Muse) 16-07-2012 63
  • 64. Functions of eicosanoids PGF2α – causes constriction of the uterus Carboprost; “Hebamate” (15-Me-PGF2α) – induces abortions PGE2 is applied locally to help induce labor at term 16-07-2012 64
  • 65. Examples of drugs derived from prostaglandi 16-07-2012 65
  • 66. Terpenes simple lipids, but lack fatty acid component formed by the combination of 2 or more molecules of 2-methyl-1,3-butadiene (isoprene) monoterpene (C-10) – made up of 2 isoprene units sesquiterpene (C-15) – made up of 3 isoprene units diterpene (C-20) – made up of 4 isoprene units 16-07-2012 66
  • 67. CHO limonene citronellal OH menthol camphene Monoterpenes are readily recognized by their characterisitic flavors and odors ( limonene in lemons, citronellal in roses and geraniums, pinene in turpentine and menthol from peppermint) 16-07-2012 67
  • 68. HO bisabolene 16-07-2012 eudesmol 68
  • 69. OH H CH2OH O HO C O phytol H3C CH3 CH3 H CH3 COOH gibberelic acid CH3 H O CH3 16-07-2012 All-trans-retinal 69
  • 70. HO H squalene lanosterol Triterpenes are C-30 compounds are addition products of 2 sesquiterpenes; Both squalene and lanosterol are precursors of cholesterol and 16-07-2012 70
  • 71. Other terpenes tetraterpenes (C-40) are not as common as mono, di, and triterpenes include the carotenoids such as beta-carotene (precursor of vitamin A) and lycopene found in tomatoes usually colorful compounds due to highly conjugated system polyisoprenoids or polyprenols consist of numerous isoprene adducts (8 – 22) examples include dolichol phosphate, undecaprenyl alcohol (bactoprenol) and the side chains of vitamins K, vitamin E and coenzyme Q 16-07-2012 71
  • 72. Thank You 16-07-2012 72