Chemistry of Lipids


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Chemistry of Lipids

  1. 1. Chemistry of Lipids Lecture No. 3
  2. 2. What are Lipids?
  3. 3. Lipids or Fats• Lipids are heterogenous group of compounds related either actually or potentially to the fatty acids.• They are water-insoluble organic substances found in cells, which are soluble in organic, non-polar solvents such as chloroform, ether, acetone, benzene, n-hexane, TCA, CCl, etc.• They are widely distributed in nature.
  4. 4. What are the functions of lipids?• The importance of lipids can be seen from their varied functions. They are:• 1. As membrane structural components• 2. As intracellular storage depots of metabolic fuel• As transport form of metabolic fuel• As regulatory substances (some hormones)• As protective form of the cell walls of many bacteria, of the leaves of higher plants, of the exoskeleton of insects and the skin of vertebrates• As enzymes cofactors (some vitamins)• As transport form of some neurotransmitters (acetylcholine)• As receptors in nerve ending membranes• As determinants of immunological specificity• As part of the outer coating between the body of the organism and the environment to prevent infection and
  5. 5. Classification of LipidsA. Classification by White – based on the presence orabsence of glycerol1. Fatty acids2. Lipids containing glycerola) Neutral fats (triacylglycerols)b) Phosphoglycerides or phospholipidsc) Cardiolipind) Plasmalogens3. Lipids not containing glycerola) Sphingolipidsb) Alipathic alcohol and waxesc) Terpenesd) Steroidse) Prostaglandins4. Lipids combined with other classes of compoundsa) lipoproteins and proteolipidsb) Glycolipids
  6. 6. Classification by Bloors 1.Simple Lipidsa) Fats and Oilsb) Waxes2. Compound Lipidsa) Phospholipidsb) Glycolipids3. Derived Lipidsa) Fatty acidsb) Alcoholc0 Sterols
  7. 7. Fatty Acids• Fatty acids are the most abundant occurring lipids. They are the building blocks of the several classes of lipids and neutral fats, phosphoglycerides, glycolipids, cholesterol esters and some waxes. They are the products of fat hydrolysis• They are mainly straight chain, alipathic, monocarboxylic acids, ranging in chain lengths from 4 -24 C atoms• Type formula: R-COOH• Fatty acids may be saturated or unsaturated
  8. 8. Fatty Acids
  9. 9. Saturated fatty acids• Saturated fatty acids belong to acetic acid series with general formula CnH2nO2 -. They contain up to 8 C and are liquid at room temperature. Longer chains of saturated FA are solids. The systematic name ends in “anoic”• Examples: Lauric or duodecanoicMyristic or tetradecanoicPalmitic or hexadecanoicStearic or octadecanoicArachidic or didecanoic
  10. 10. Triacylglycerols (TAG)• Storage of fatty acids in organisms is largely in the form of TAG or fats.• These substances are triesters of fatty acids and glycerol.• The long chains of fatty acids are extraordinarily for energy storage, because they contain C in a fully reduced form and will therefore yield a maximum amount of energy on oxidation.
  11. 11. Unsaturated fatty acids• Unsaturated fatty acids contain double bond and their systematic names end in “enoic.” They are unstable and reactive due to the presence of the double bond – therefore they are capable of taking up molecules of H2O, H, I2, O2, B2 at each double bond• Double bonds in naturally occurring fatty acids are always in a cis- form as opposed to trans- configuration.• The presence of the double bond gives rise to the possibility of geometric isomerism
  12. 12. Oleic acidOleic acid isCH3(CH2)7CH=CH(CH2)7COOHOleic acid is the most abundant fatty acid innature forming about 50% of the total fattyacids in many fats and is found in allnaturally existing fats
  13. 13. Indispensable fatty acids• The body has the ability to desaturate fatty acids but more unsaturated fatty acids which are necessary for nutrition and growth can be formed in the body.• They have to be supplied from the diet.• They become indispensable items in the diet.• These are linoleic acid, linolenic acid and arachidonic acid.
  14. 14. Indispensable fatty acids• Linoleic acid – cis-9 octadecadienoic acid18:2,9,12• Linolenic acid – 1,5 octadecatrienoic acid18:3,9,12,15• Arachidonic acid – cis-5,8,11,14eicosatetraenoic acid20:4,5,8,11,14
  15. 15. Glycerophospholipids or Phosphoglycerides• They are the major class of naturally occurring phospholipids, lipids with phosphate-containing head groups.• These compounds make up a significant fraction of the membrane lipids throughout the bacterial, plant and animal kingdoms.• Examples are: phosphotidyl choline, phosphotidylethanolamine, phosphotidylserine, phosphotidylinositol
  16. 16. Cardiolipin & Plasmalogens • Cardiolipin consists of 2 molecules of phosphatidic acid connected by a glycerol bridge • It is of immunological importance • Plasmalogens make up 10% of the phospholipids of the brain and muscles. • They are phospholipids where alkyl ether is attached at alpha position of glycerol. • Three principal classes of plasmalogens are:1. phosphotidalcholine2. phosphotidalserine3. phosphotidal ethanolamine
  17. 17. Plasmalogens
  18. 18. Sphingolipids • They are comlex lipids containing sphingosine or a related base, as their backbone • All sphingolipids contain 3 characteristics:1. 1 molecule of fatty acid2. 1 molecule of sphingosine or 1 of itsderivatives3. a polar head group • The greatest concentration of sphingolipids is found in the CNS, particularly in the white matter, although all human tissues contain some. • Kinds of sphingolipids are:1. Shingomyelin2. Glycosphingolipida) Gangliosideb) Cerebroside
  19. 19. Sphingomyelin
  20. 20. Ceramide
  21. 21. Chemical Reaction of Lipids
  22. 22. Steroids• Steroids are found in association with fats and separated from the fats after saponification in the “unsaponifiable residue.”• They all possess similar cyclic nucleus resembling phenanthrene (rings A, B, and C), to which a cyclopentane ring is attached• Steroid nucleus is cyclopentanoperhydrophenanthrene• There is an oxygenated substituent on C3 which is shared by almost all naturally occurring steroids.
  23. 23. Biologically Important Steroids• Sterols – Cholesterol, ergosterol, lanosterol• Bile Acids – cholic acid, glycholic acid,• Adrenocortical Hormones – costicosterone, cortisol, aldosterone• Sex hormones – androgen, estrogen• Vitamins – Vitamin D, K
  24. 24. Lanosterol and Ergosterol
  25. 25. Cholesterol• Cholesterol is widely distributed in cells particularly in the nervous tissue• It is the major component of the plasma membrane.• It is the parent compound of all steroids synthesized in the body.• It occurs in animal fats, but not in plant fats.
  26. 26. Cholesterol
  27. 27. Estrogen• Estrogen differs from all steroids in that ring A is aromatic• Hydroxyl group at position 3 is phenolic rather than alcoholic• Because of this fact, estrogens behave like weak acids and are extractable from benzene solution with aqueous alkali
  28. 28. Androgen or Testosterone• Androgen or male sex hormone is C19 steroid and belongs to the class of steroids devoid of C side chain at C17• Synthesized from the testis• Has a OH in C17
  29. 29. Testosterone It is also called androgen. It is C19 steroid. This is a steroid without a carbon side chain at position 17.
  30. 30. Progesterone• It is also an adrenal cortex hormone and a C21 steroid• But it has CH3 instead of the CH2OH of corticosterone
  31. 31. Cortisosterone It is a C21 steroid Contains 2 carbon atoms in the side chain at position 17
  32. 32. Bile Acids• Bile acids or salts are steroids in nature. Four different salts occur in human bile: Glycocholic acid, deoxycholic acid, cholic acid and lithocholic acid• They are strong emulsifying agent that help disperse fatty materials• They stimulate intestinal motility
  33. 33. Bile Acids• Cholic acid Deoxycholic acid
  34. 34. Terpenes
  35. 35. Terpenes
  36. 36. Examples of Terpenes Monoterpene - limonene Diterpene – phytol Triterpene – squalene Tetraterpene – α,ß,γ- carotene Polyterpene – natural rubber, gutta perchae
  37. 37. Vitamin D• Vitamin D2 Vitamin D3
  38. 38. Vitamin K
  39. 39. Vitamin K2
  40. 40. Prostaglandins• They are family of fatty acids which have hormonal or regulatory nature.• The best known prostaglandins are PGE1PGF1a PGF2a• The prostaglandins differ from each other with respect to their biological activity, although all show at least some activity in lowering blood pressure and inducing muscles to contract
  41. 41. Thromboxane A2
  42. 42. Leukotrienes
  43. 43. Micelle
  44. 44. Micelles• When fatty acids are placed in water, they appear to dissolve, they are not, in true solution, but present as micelles.• Micelles or microscopic fat cells have the properties of bisolubility.• Bile acids are strong emulsifying agents that help dispense fatty acids into micelles, which may be absorbed or more rapidly broken down by enzymes.
  45. 45. Lipids in Cell Membranes
  46. 46. Chemical tests for Lipids• Liebermann-Burchard test - for cholesterol• Acrolein test – for glycerol• Saponication – fats react with alkali to produce metallic salt of fatty acid or soap• Halogenation – when halogens are added to the double bond of unsaturated FA, the reaction proceeds spontaneously in a given suitable solvent.• Hydrogenation – when unsaturated FA are hydrogenated in the presence of catalyst like Pt, Pa, or Ni
  47. 47. Biological Significance of Lipids• The current biological significance of lipids can be seen in the following:• 1. Obesity• 2. Arteriosclerosis• Role of polyunsaturated fatty acids (PUFA)in nutrition and health