Chemistry of lipids

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Chemistry of lipids

  1. 1. Chemistry of LipidsChemistry of Lipids
  2. 2. Chemistry of LipidsChemistry of Lipids Definition: - Lipids are organic compounds formed mainly from alcohol and fatty acids combined together by ester linkage. CH2R Fattyalcohol OH C R Fattyacid HO O + H2O CH2R O C R O Esterase (lipase) ester (lipid)
  3. 3. - Lipids are insoluble in water, but soluble in fat or organic solvents (ether, chloroform, benzene, acetone). - Lipids include fats, oils, waxes and related compounds. They are widely distributed in nature both in plants and in animals.
  4. 4. Bi ol ogi cal Import ance of Li pi ds: 1. They are more palatable and storable to unlimited amount compared to carbohydrates. 2. They have a high-energy value (25% of body needs) and they provide more energy per gram than carbohydrates and proteins but carbohydrates are the preferable source of energy. 3. Supply the essential fatty acids that cannot be synthesized by the body. 4. Supply the body with fat-soluble vitamins (A, D, E and K). 5. They are important constituents of the nervous system. 6. Tissue fat is an essential constituent of cell membrane and nervous system. It is mainly phospholipids in nature that are not affected by starvation.
  5. 5. 7-Stored lipids “depot fat” is stored in all human cells acts as:  A store of energy.  A pad for the internal organs to protect them from outside shocks.  A subcutaneous thermal insulator against loss of body heat. 8-Lipoproteins, which are complex of lipids and proteins, are important cellular constituents that present both in the cellular and subcellular membranes. 9-Cholesterol enters in membrane structure and is used for synthesis of adrenal cortical hormones, vitamin D3 and bile acids. 10- Lipids provide bases for dealing with diseases such as obesity, atherosclerosis, lipid-storage diseases, essential fatty acid deficiency, respiratory distress syndrome
  6. 6. Classification of LipidsClassification of Lipids 1. Si mpl e l i pi ds ( Fat s & Waxes) 2. Compl ex ( compound or conj ugat ed l i pi ds) 3. Deri ved Li pi ds 4. Li pi d- associ at i ng subst ances
  7. 7. But first,But first,
  8. 8. Fatty alcoholsFatty alcohols (glycerol &(glycerol & sphingosine)sphingosine) Glycerol: a trihydric alcohol (i.e., containing three OH groups) and has the popular name glycerin. It is synthesized in the body from glucose.  It has the following properties:
  9. 9. 1. Colorless viscous oily liquid with sweet taste. 2. On heating with sulfuric acid or KHSO4 (dehydration) it gives acrolein that has a bad odor. This reaction is used for detection of free glycerol or any compound containing glycerol. CH2 OH CH CH2 OH HO CHO CH CH2 2 H2O Heating, KHSO4 Glycerol Acrolein
  10. 10. 3-It combines with three molecules of nitric acid to form trinitroglycerin (TNT) that is used as explosive and vasodilator. 4-On esterification with fatty acids it gives:  Monoglyceride or monoacyl-glycerol: one fatty acid + glycerol.  Diglyceride or diacyl-glycerol: two fatty acids + glycerol.  Triglyceride or triacyl-glycerol: three fatty acids + glycerol. 5-It has a nutritive value by conversion into glucose and enters in structure of phospholipids.
  11. 11. Uses of Glycerol:Uses of Glycerol: 1. pharmaceutical and cosmetic preparations. 2. Reduces brain edema in cerebrovascular disease. 3. Nitroglycerin is used as vasodilator especially for the coronary arteries, thus it is used in treatment of angina pectoris. 4. explosives manufacturing. 5. treatment of glaucoma (increased intraocular pressure)due to its ability to dehydrate the tissue from its water content.
  12. 12. Sphingosine:Sphingosine: - the alcohol(monohydric) present in sphingolipids. - synthesized in the body from serine and palmitic acid. It is not positive with acrolein test. CH CH NH2 CH2OH CHCH(CH2)12CH3 OH Sphingosine
  13. 13. Fatty AcidsFatty Acids DefinitionDefinition: aliphatic mono-carboxylic acids that are mostly obtained from the hydrolysis of natural fats and oils. the general formula R-(CH2)n-COOH and mostly have straight chain (a few exceptions have branched and heterocyclic chains). "n" is mostly an even number of carbon atoms (2-34)
  14. 14. Classification ofClassification of FATTY ACIDSFATTY ACIDS According to presence orAccording to presence or absence of double bondsabsence of double bonds they are classified intothey are classified into:: >SatURATED FA >unsatURATED FA
  15. 15. 1-Saturated Fatty Acids no double bonds with 2-24 or more carbons. solid at RT except if they are short chained. may be even or odd numbered. molecular formula, CnH2n+1COOH.
  16. 16. Saturated Fatty acids could be: A-Short chain Saturated F.A.A-Short chain Saturated F.A. (2-10(2-10 carbon).carbon). a-Short chain Saturated volatile F.A.(2-6 C). b-Short chain Saturated non volatile F.A.(7-10 C). B-Long chain Saturated F.AB-Long chain Saturated F.A. (more than. (more than 10 carbon)10 carbon)
  17. 17. A-A- SATurated- short chainSATurated- short chain VolatileVolatile short-chainshort-chain fattyfatty acids:acids:  liquid in nature and containliquid in nature and contain 1-6 C1-6 C  water-solublewater-soluble volatile at room temperaturevolatile at room temperature  e.g., acetic, butyric,& caproic acids.e.g., acetic, butyric,& caproic acids. Acetic F.A. (2C ) CHAcetic F.A. (2C ) CH33-COOH.-COOH. Butyric F.A. (4C ) CHButyric F.A. (4C ) CH33-(CH-(CH22))22-COOH.-COOH. Caproic F.A. (6C ) CHCaproic F.A. (6C ) CH33-(CH-(CH22))44-COOH.-COOH.
  18. 18. A- Saturated- Short chain Non-volatileNon-volatile short-chainshort-chain fattyfatty acidsacids: solids at room temperaturesolids at room temperature containcontain 7-107-10 carbons.carbons. water-solublewater-soluble  non-volatile at RTnon-volatile at RT include caprylic and capric F.A.include caprylic and capric F.A. caprylic (8 C ) CHcaprylic (8 C ) CH33-(CH-(CH22))66-COOH.-COOH. Capric (10 C ) CHCapric (10 C ) CH33-(CH-(CH22))88-COOH.-COOH.
  19. 19. B-B- Saturated- LONG CHAINSaturated- LONG CHAIN Long-chain fatty acids: >10 carbon atoms. in hydrogenated oils, animal fats, butter and coconut and palm oils. non-volatile water-insoluble E.g. palmitic, stearic, & lignoceric F.A.  palmitic(16C) CHpalmitic(16C) CH33-(CH-(CH22))1414-COOH-COOH stearic (18 C ) CHstearic (18 C ) CH33-(CH-(CH22))1616-COOH-COOH lignoceric (24C ) CHlignoceric (24C ) CH33-(CH-(CH22))2222-COOH-COOH
  20. 20. 2-Unsaturated Fatty Acids - contain double bond - TYPES: A. monounsaturated they contain one double bond . (CnH2n-1 COOH) B. polyunsaturated they contain more the one double bond (CnH2n-# COOH).
  21. 21. A-Monounsaturated fatty acids: 1-Palmitoleic acid :  It is found in all fats.  It is C16:1∆9, i.e., has 16 carbons and one double bond located at carbon number 9 and involving carbon 10. CHCH33-( CH-( CH22 ))55CH = CH-(CHCH = CH-(CH22))77 –COOH–COOH
  22. 22. 2-Oleic acid Is the most common fatty acid inIs the most common fatty acid in natural fats.natural fats. It isIt is C18:1∆9C18:1∆9, i.e., has 18 carbons and, i.e., has 18 carbons and one double bond located at carbonone double bond located at carbon number 9 and involving carbon 10.number 9 and involving carbon 10. CHCH33-(CH-(CH22))77- CH=CH – (CH- CH=CH – (CH22))77-COOH-COOH
  23. 23. 3-Nervonic acid (Unsaturated lignoceric acid).  It is found in cerebrosides.  It is C24:1∆15, i.e., has 24 carbons and one double bond located at carbon number 15 and involving carbon 16. CHCH33 – (CH– (CH22))77 CH= CH – (CHCH= CH – (CH22))1313- COOH- COOH
  24. 24. B-Polyunsaturated fatty acids : (Essential fatty acids):  Definition:  They are essential fatty acids that can not be synthesized in the human body and must be taken in adequate amounts in the diet.  They are required for normal growth and metabolism
  25. 25. Source: vegetable oils such as corn oil, linseed oil, peanut oil, olive oil, cottonseed oil, soybean oil and many other plant oils, cod liver oil and animal fats.  Deficiency: Their deficiency in the diet leads to nutrition deficiency disease. Symptoms:Symptoms: poor growth and health with susceptibility to infections, dermatitis, decreased capacity to reproduce, impaired transport of lipids, fatty liver, and lowered resistance to stress.
  26. 26. FunctionFunction of Essential Fatty Acids:of Essential Fatty Acids: 1.They are useful in the treatment of atherosclerosis by help transporting blood cholesterol and lowering it and transporting triglycerides. 2.The hormones are synthesized from them. 3.They enter in structure of all cellular and subcellular membranes and the transporting plasma phospholipids. 4.They are essential for skin integrity, normal growth and reproduction. 5.They have an important role in blood clotting (intrinsic factor). 6.Important in preventing and treating fatty liver. 7.Important role in health of the retina and vision. 8.They can be oxidized for energy production.
  27. 27. POLYUnsat FA: 1-Linoleic:1-Linoleic: C18:2∆9, 12.  It is the most important since other essential fatty acids can be synthesized from it in the body. CHCH33-(CH-(CH22))44-CH = CH-CH-CH = CH-CH22-CH=CH-(CH-CH=CH-(CH22))77-- COOHCOOH
  28. 28. POLYUnsat FA: 2-Linolenic acid2-Linolenic acid: C18:3∆9, 12, 15, in corn, linseed, peanut, olive, cottonseed and soybean oils. CHCH33-CH-CH22-CH=CH-CH-CH=CH-CH22-CH=CH-CH-CH=CH-CH22-- CH=CH-(CHCH=CH-(CH22))77-COOH-COOH
  29. 29. POLYUnsat FA: 3-Arachidonic acid3-Arachidonic acid: C20:4∆5, 8, 11, 14.  It is an important component of phospholipids in animal and in peanut oil from which prostaglandins are synthesized. CHCH33-(CH-(CH22))44-CH=CH-CH-CH=CH-CH22-CH=CH-CH-CH=CH-CH22-- CH=CH-CHCH=CH-CH22-CH=CH-(CH-CH=CH-(CH22))33-COOH-COOH
  30. 30. Classification of LipidsClassification of Lipids 1. Si mpl e l i pi ds ( Fat s & Waxes) 2. Compound or conj ugat ed l i pi ds 3. Deri ved Li pi ds 4. Li pi d- associ at i ng subst ances
  31. 31. Classification of LipidsClassification of Lipids 1. Si mpl e l i pi ds ( Fat s & Waxes)
  32. 32. SimpleLipidsSimpleLipids A-Neutral Fats and oilsA-Neutral Fats and oils (Triglycerides)(Triglycerides) Definition:Definition: Neutral- uncharged due to absence ofNeutral- uncharged due to absence of ionizable groups in it.ionizable groups in it. most abundant lipids in nature.most abundant lipids in nature. constitute about 98% of the lipids ofconstitute about 98% of the lipids of adipose tissue, 30% of plasma or liveradipose tissue, 30% of plasma or liver lipids, less than 10% of erythrocytelipids, less than 10% of erythrocyte lipids.lipids.
  33. 33. They are esters of glycerol with various fatty acids.They are esters of glycerol with various fatty acids. Since the 3 hydroxyl groups of glycerol are esterified,Since the 3 hydroxyl groups of glycerol are esterified, the neutral fats are also calledthe neutral fats are also called “Triglycerides”.“Triglycerides”.  Esterification of glycerol with one moleculeEsterification of glycerol with one molecule of fatty acid givesof fatty acid gives monoglyceridemonoglyceride, and that, and that with 2 molecules giveswith 2 molecules gives diglyceridediglyceride.. H2C O C HO H2C C C O C R1 R3 R2 O O O + 3 H2O CH2 OH C HHO CH2 OH HO C R1 O HO C R3 O HO C R2 O Fatty acids Glycerol Triglycerides (Triacylglycerol)
  34. 34. Types of triglyceridesTypes of triglycerides 1-Simple triglycerides1-Simple triglycerides:: If the three fattyIf the three fatty acids connected to glycerol are of the same type theacids connected to glycerol are of the same type the triglyceride is called simple triglyceride, e.g.,triglyceride is called simple triglyceride, e.g., tripalmitin.tripalmitin. 2-Mixed triglycerides2-Mixed triglycerides:: if they are of differentif they are of different types, it is called mixed triglycerides, e.g., stearo-types, it is called mixed triglycerides, e.g., stearo- diolein and palmito-oleo-stearin.diolein and palmito-oleo-stearin. >> Natural fatsNatural fats are mixtures of mixed triglyceridesare mixtures of mixed triglycerides with a small amount of simple triglycerides.with a small amount of simple triglycerides.
  35. 35. CH2 O C HO CH2 C C O C (CH2)14 O O O Tripalmitin (simple triacylglycerol) CH3 (CH2)14CH3 (CH2)14 CH3 CH2 O C HO CH2 C C O C (CH2)16 O O O 1-Stearo-2,3-diolein (mixed triacylglycerol) CH3 (CH2)7CHCH(CH2)7CH3 (CH2)7 CH CH (CH2)7 CH3 CH2 O C HO CH2 C C O C (CH2)14 O O O 1-palmito-2-oleo-3-stearin (mixed triacylglycerol) CH3 (CH2)16 CH3 (CH2)7CHCH(CH2)7CH3
  36. 36.  The commonest fatty acids in animal fatsThe commonest fatty acids in animal fats areare palmitic, stearic and oleic acids.palmitic, stearic and oleic acids. The main difference between fats and oilsThe main difference between fats and oils is foris for oils being liquidoils being liquid at roomat room temperature, whereas,temperature, whereas, fats are solids.fats are solids.  This is mainly due to presence of largerThis is mainly due to presence of larger percentage ofpercentage of unsaturatedunsaturated fatty acids infatty acids in oils than fats that has mostlyoils than fats that has mostly saturatedsaturated fatty acids.fatty acids.
  37. 37. PhysicalPhysical properties of fat andproperties of fat and oils:oils: 1. Freshly prepared fats and oils are colorless, odorless and tasteless.Any color, or taste is due to association with other foreign substances, e.g., the yellow color of body fat or milk fat is due to carotene pigments(cow milk). 2. Fats have specific gravity less than 1 (one) and, therefore, they float on water. 3. Fats are insoluble in water, but soluble in organic solvents as ether and benzene. 4. Melting points of fats are usually low, but higher than the solidification point,
  38. 38. ChemicalChemical Properties of fats andProperties of fats and oilsoils: 1-Hydrolysis:1-Hydrolysis:  hydrolyzed into their constituents (hydrolyzed into their constituents (fatty acids and glycerol)fatty acids and glycerol) byby heated steam, acid, alkali or enzyme (e.g., lipase of pancreas).heated steam, acid, alkali or enzyme (e.g., lipase of pancreas).  - During their enzymatic and acid hydrolysis glycerol and free- During their enzymatic and acid hydrolysis glycerol and free fatty acids are produced.fatty acids are produced. CH2 O C HO CH2 C C O C R1 R3 R2 O O O 3 H2O H2C OH C HHO H2C OH OHCR1 O OHCR3 O + OHCR2 OLipase or Acid Triacylglycerol Glycerol Free fatty acids
  39. 39. 2-Saponification. >>Alkaline hydrolysis produces glycerol and salts ofAlkaline hydrolysis produces glycerol and salts of fatty acids (fatty acids (soapssoaps).). Soaps cause emulsification of oily material this helpSoaps cause emulsification of oily material this help easy washing of the fatty materialseasy washing of the fatty materials CH2 O C HO CH2 C C O C R1 R3 R2 O O O H2C OH C HHO H2C OH ONaCR1 O ONaCR3 O + ONaCR2 O Triacylglycerol Glycerol Sodium salts of fatty acids (soap) 3 NaOH
  40. 40. 3-Halogenation3-Halogenation  Neutral fats containing unsaturated fatty acids have theNeutral fats containing unsaturated fatty acids have the ability of adding halogens (e.g., hydrogen or hydrogenationability of adding halogens (e.g., hydrogen or hydrogenation and iodine or iodination) at the double bonds.and iodine or iodination) at the double bonds.  very important property to determine the degree ofvery important property to determine the degree of unsaturation of the fat or oil that determines its biologicalunsaturation of the fat or oil that determines its biological valuevalue CH (CH2)7 COOHCHCH2CH Linoleic acid CH(CH2)4CH3 2 I2 CH (CH2)7 COOHCHCH2CH Stearate-tetra-iodinate CH(CH2)4CH3 II I I
  41. 41. 4-Hydrogenation or4-Hydrogenation or hardening of oilshardening of oils: It is a type of addition reactions accepting hydrogenIt is a type of addition reactions accepting hydrogen at the double bonds of unsaturated fatty acids.at the double bonds of unsaturated fatty acids. The hydrogenation is done under high pressure ofThe hydrogenation is done under high pressure of hydrogen and is catalyzed by finely divided nickel orhydrogen and is catalyzed by finely divided nickel or copper and heat.copper and heat. It is the base of hardening of oils (It is the base of hardening of oils (margarinemargarine manufacturingmanufacturing), e.g., change of oleic acid of fats), e.g., change of oleic acid of fats (liquid) into stearic acid (solid).(liquid) into stearic acid (solid). It is advisable not to saturate all double bonds;It is advisable not to saturate all double bonds; otherwise margarine produced will be very hard, ofotherwise margarine produced will be very hard, of very low biological value and difficult to digest.very low biological value and difficult to digest.
  42. 42. Oils (liquid) (with unsaturated fatty acids, e.g., oleic) Hard fat (margarine, solid) (with saturated fatty acids, e.g., stearic) Hydrogen, high pressure, nickel Advantages forAdvantages for hydrogenatedhydrogenated oil or fatoil or fat are as followsare as follows:: 1.1. It is more pleasant as cooking fat.It is more pleasant as cooking fat. 2.2. It is digestible and utilizable as normal animal fats and oils.It is digestible and utilizable as normal animal fats and oils. 3.3. It is less liable to cause gastric or intestinal irritation.It is less liable to cause gastric or intestinal irritation. 4.4. It is easily stored and transported and less liable toIt is easily stored and transported and less liable to rancidity.rancidity. Disadvantages of hydrogenatedDisadvantages of hydrogenated  fats include lack of fat-soluble vitamins (A, D, E and K) andfats include lack of fat-soluble vitamins (A, D, E and K) and essential fatty acidsessential fatty acids
  43. 43. 5-Oxidation (Rancidity)5-Oxidation (Rancidity) This toxic reaction of triglycerides leads to unpleasant odour or taste of oils and fats developing after oxidation by oxygen of air, bacteria, or moisture. Also this is the base of the drying oils after exposure to atmospheric oxygen. Example is linseed oil, which is used in paints and varnishes manufacturing = RANCID
  44. 44. RancidityRancidity Definition:Definition: physico-chemical changephysico-chemical change development ofdevelopment of unpleasant odor or taste or abnormalunpleasant odor or taste or abnormal colorcolor particularly on agingparticularly on aging exposure to atmospheric oxygen, light, moisture,exposure to atmospheric oxygen, light, moisture, bacterial or fungal contamination and/or heat.bacterial or fungal contamination and/or heat.  Saturated fats resist rancidity more thanSaturated fats resist rancidity more than unsaturated fats that have unsaturatedunsaturated fats that have unsaturated double bonds.double bonds.
  45. 45. Types and causes of RancidityTypes and causes of Rancidity: 1.1. Hydrolytic rancidityHydrolytic rancidity 2.2. Oxidative rancidityOxidative rancidity 3.3. Ketonic rancidityKetonic rancidity 1-Hydrolytic rancidity1-Hydrolytic rancidity:  from slight hydrolysis of the fat by lipasefrom slight hydrolysis of the fat by lipase  bacterial contamination leading to thebacterial contamination leading to the liberation ofliberation of free fatty acids and glycerolfree fatty acids and glycerol at high temp andat high temp and moisture.moisture.  Volatile short-chain fatty acids have unpleasantVolatile short-chain fatty acids have unpleasant odor.odor.
  46. 46. CH2 O C HO CH2 C C O C R1 R3 R2 O O O 3 H2O H2C OH C HHO H2C OH OHCR1 O OHCR3 O + OHCR2 OLipase Triacylglycerol Glycerol Free fatty acids (volatile, bad odor)
  47. 47. 2-Oxidative Rancidity2-Oxidative Rancidity: oxidation of fat or oiloxidation of fat or oil by exposure to oxygen, light and/or heat producingby exposure to oxygen, light and/or heat producing peroxide derivativesperoxide derivatives e.g.,e.g., peroxides, aldehydes, ketones and dicarboxylicperoxides, aldehydes, ketones and dicarboxylic acids that are toxic and have bad odor.acids that are toxic and have bad odor. due to oxidative addition of oxygen at thedue to oxidative addition of oxygen at the unsaturated double bond of unsaturated fatty acidunsaturated double bond of unsaturated fatty acid of oils.of oils.
  48. 48. Polyunsaturated fatty acid Peroxyradical Oxidant, O2 Hydroperoxide Hydroxy fatty acid Cyclic peroxide Aldehydes such as malondialdehyde Other fragments such as dicarboxylic acids
  49. 49. 3-Ketonic Rancidity: due to the contamination with certain fungi such asdue to the contamination with certain fungi such as Aspergillus nigerAspergillus niger on fats such ason fats such as coconut oilcoconut oil..  Ketones, fatty aldehydes, short chain fatty acidsKetones, fatty aldehydes, short chain fatty acids and fatty alcohols are formed.and fatty alcohols are formed. Moisture accelerates ketonic rancidity.Moisture accelerates ketonic rancidity.
  50. 50. Prevention of rancidityPrevention of rancidity Avoidance of the causes (Avoidance of the causes ( exposure to light,exposure to light, oxygen, moisture, high temperature andoxygen, moisture, high temperature and bacteria or fungal contaminationbacteria or fungal contamination ).). By keeping fats or oils in well-closed containers in cold, darkBy keeping fats or oils in well-closed containers in cold, dark and dry place (i.e.,and dry place (i.e., good storage conditions).good storage conditions). Removal of catalysts such as lead andRemoval of catalysts such as lead and copper that catalyze rancidity.copper that catalyze rancidity. Addition ofAddition of anti-oxidantsanti-oxidants to prevent peroxidation in fat (i.e.,to prevent peroxidation in fat (i.e., rancidity). They include phenols, naphthols, tannins andrancidity). They include phenols, naphthols, tannins and hydroquinones.hydroquinones. The most common natural antioxidant is vitaminThe most common natural antioxidant is vitamin E that is importantE that is important in vitroin vitro andand in vivoin vivo..
  51. 51. Hazards of Rancid Fats: 1.1. The products of rancidity areThe products of rancidity are toxic,toxic, i.e.,i.e., causescauses food poisoning and cancerfood poisoning and cancer.. 2.2. Rancidity destroys the fat-solubleRancidity destroys the fat-soluble vitamins (vitamins (vitamins A, D, K and Evitamins A, D, K and E).). 3.3. Rancidity destroys theRancidity destroys the polyunsaturatedpolyunsaturated essential fatty acidsessential fatty acids.. 4.4. Rancidity causesRancidity causes economical losseconomical loss because rancid fat is inedible.because rancid fat is inedible.
  52. 52. B-WaxesB-Waxes DefinitionDefinition: Waxes are solid simple lipidsWaxes are solid simple lipids containing a monohydric alcohol (with acontaining a monohydric alcohol (with a higher molecular weight than glycerol)higher molecular weight than glycerol) esterified to long-chain fatty acids.esterified to long-chain fatty acids. Examples of these alcohols areExamples of these alcohols are palmitoylpalmitoyl alcohol, cholesterol, vitamin A or D.alcohol, cholesterol, vitamin A or D. Properties of waxesProperties of waxes: Waxes are: Waxes are insoluble in water, but soluble in fatinsoluble in water, but soluble in fat solvents and are negative for acroleinsolvents and are negative for acrolein test.test. Waxes are not easily hydrolyzed as theWaxes are not easily hydrolyzed as the fats and are indigestible by lipases andfats and are indigestible by lipases and are very resistant to rancidity.are very resistant to rancidity. Thus they are of no nutritional value.Thus they are of no nutritional value.
  53. 53. Type of WaxesType of Waxes: - Waxes are widely distributed in nature such as the secretion of certain insects as bees-wax, protective coatings of the skins and furs of animals and leaves and fruits of plants. They are classified into true- waxes and wax-like compounds as follows: A-True waxesA-True waxes: include: Bees-waxBees-wax is secreted by the honeybees that use it to form the combs. It is a mixture of waxes with the chief constituent is mericyl palmitate.
  54. 54. C15H31 C OH O +C30H61OH C15H31 C O O C30H61 H2OPalmitic acid Mericyl alcohol Mericyl palmitate B-Wax-like compounds:  Cholesterol estersCholesterol esters: Lanolin (or woolLanolin (or wool fat) is prepared from the wool-fat) is prepared from the wool- associated skin glands and isassociated skin glands and is secreted by sebaceous glands of thesecreted by sebaceous glands of the skin.skin.  It is very complex mixture, containsIt is very complex mixture, contains both free and esterified cholesterol,both free and esterified cholesterol, e.g., cholesterol-palmitate and othere.g., cholesterol-palmitate and other sterolssterols.
  55. 55. Differences between neutral lipids and waxes: Waxes Neutral lipidsNeutral lipids 1.1.Digestibility:Digestibility: Indigestible (notIndigestible (not hydrolyzed by lipase).hydrolyzed by lipase). Digestible (hydrolyzed by lipase).Digestible (hydrolyzed by lipase). 2-Type of2-Type of alcoholalcohol:: Long-chain monohydricLong-chain monohydric alcohol + one fatty acid.alcohol + one fatty acid. Glycerol (trihydric) + 3 fatty acidsGlycerol (trihydric) + 3 fatty acids 3-Type of fatty3-Type of fatty acidsacids:: Fatty acid mainly palmiticFatty acid mainly palmitic or stearic acid.or stearic acid. Long and short chain fatty acids.Long and short chain fatty acids. 4-Acrolein test4-Acrolein test: Negative.Negative. Positive.Positive. 5-Rancidability:5-Rancidability: Never get rancid.Never get rancid. Rancidible.Rancidible. 6-Nature at6-Nature at roomroom temperaturetemperature. Hard solid.Hard solid. Soft solid or liquid.Soft solid or liquid. 7-Saponification7-Saponification Nonsaponifiable.Nonsaponifiable. Saponifiable.Saponifiable. 8-Nutritive8-Nutritive valuevalue: No nutritive value.No nutritive value. Nutritive.Nutritive. 9-Example:9-Example: Bee & carnuba waxes.Bee & carnuba waxes. Butter and vegetable oils.Butter and vegetable oils.
  56. 56. 2-Compound Lipids2-Compound Lipids DefinitionDefinition:  They are lipids that containThey are lipids that contain additional substances, e.g., sulfur,additional substances, e.g., sulfur, phosphorus, amino group,phosphorus, amino group, carbohydrate, or proteins besidecarbohydrate, or proteins beside fatty acid and alcohol.fatty acid and alcohol.  Compound or conjugated lipids areCompound or conjugated lipids are classified into the following typesclassified into the following types according to the nature of theaccording to the nature of the additional group:additional group: 1.1. PhospholipidsPhospholipids 2.2. Glycolipids.Glycolipids. 3.3. LipoproteinsLipoproteins 4.4. Sulfolipids and amino lipids.Sulfolipids and amino lipids.
  57. 57. A-PhospholipidsA-Phospholipids Definition:Definition: Phospholipids or phosphatides arePhospholipids or phosphatides are compound lipids, which contain phosphoriccompound lipids, which contain phosphoric acid group in their structureacid group in their structure.. ImportanceImportance: 1.1.They are present in large amounts in theThey are present in large amounts in the liver and brain as well as blood. Everyliver and brain as well as blood. Every animal and plant cell containsanimal and plant cell contains phospholipids.phospholipids. 2.2.The membranes bounding cells andThe membranes bounding cells and subcellular organelles are composed mainlysubcellular organelles are composed mainly of phospholipids. Thus, the transfer ofof phospholipids. Thus, the transfer of substances through these membranes issubstances through these membranes is controlled by properties of phospholipids.controlled by properties of phospholipids. 3.3.They are important components of theThey are important components of the lipoprotein coat essential for secretion andlipoprotein coat essential for secretion and transport of plasma lipoprotein complexes.transport of plasma lipoprotein complexes. Thus, they are lipotropic agents thatThus, they are lipotropic agents that preventprevent fatty liverfatty liver.. 4.4.Myelin sheath of nerves is rich withMyelin sheath of nerves is rich with phospholipids.phospholipids.
  58. 58. 5-Important in digestion and5-Important in digestion and absorption of neutral lipids andabsorption of neutral lipids and excretion of cholesterol in the bile.excretion of cholesterol in the bile. 6-Important function in blood clotting6-Important function in blood clotting and platelet aggregation.and platelet aggregation. 7-They provide lung alveoli with7-They provide lung alveoli with surfactants that prevent itssurfactants that prevent its irreversible collapseirreversible collapse.. 8-Important role in signal transduction8-Important role in signal transduction across the cell membrane.across the cell membrane. 9-Phospholipase A2 in snake venom9-Phospholipase A2 in snake venom hydrolyses membrane phospholipidshydrolyses membrane phospholipids into hemolytic lysolecithin orinto hemolytic lysolecithin or lysocephalin.lysocephalin. 10-They are source of polyunsaturated10-They are source of polyunsaturated fatty acids for synthesis offatty acids for synthesis of eicosanoids.eicosanoids.
  59. 59. Sources:Sources: They are found in all cellsThey are found in all cells (plant and animal), milk and egg-(plant and animal), milk and egg- yolk in the form of lecithins.yolk in the form of lecithins. StructureStructure: phospholipids are composedphospholipids are composed of:of: 1.1. Fatty acidsFatty acids (a saturated and an(a saturated and an unsaturated fatty acid).unsaturated fatty acid). 2.2. Nitrogenous baseNitrogenous base (choline, serine,(choline, serine, threonine, or ethanolamine).threonine, or ethanolamine). 3.3. Phosphoric acid.Phosphoric acid. 4.4. Fatty alcoholsFatty alcohols (glycerol, inositol or(glycerol, inositol or sphingosine).sphingosine).
  60. 60.  Classification of PhospholipidsClassification of Phospholipids areare classified into 2 groups according toclassified into 2 groups according to the type of thethe type of the alcoholalcohol present intopresent into two types:two types: A-A-GlycerophospholipidsGlycerophospholipids: They areThey are regarded as derivatives of phosphatidicregarded as derivatives of phosphatidic acids that are the simplest type ofacids that are the simplest type of phospholipids and include:phospholipids and include: 1.1. Phosphatidic acidsPhosphatidic acids.. 2.2. LecithinsLecithins 3.3. CephalinsCephalins.. 4.4. PlasmalogensPlasmalogens.. 5.5. InositidesInositides.. 6.6. CardiolipinCardiolipin. B-SphingophospholipidsB-Sphingophospholipids: They containThey contain sphingosine as an alcohol and are namedsphingosine as an alcohol and are named SphingomyelinsSphingomyelins.
  61. 61. A-GlycerophospholipidsA-Glycerophospholipids 1-Phosphatidic acids:1-Phosphatidic acids:They are metabolicThey are metabolic intermediates in synthesis of triglyceridesintermediates in synthesis of triglycerides and glycerophospholipids in the body andand glycerophospholipids in the body and may have function as amay have function as a second messengersecond messenger.. They exist in two forms according to theThey exist in two forms according to the position of the phosphateposition of the phosphate CH2 O C HO CH2 C C O P R1 R2 O O α-Phosphatidic acid OH OH O Saturated fatty acidPolyunsaturated fatty acid Phosphate CH2 O C H CH2 C O R1 O β-Phosphatidic acid Saturated fatty acid Polyunsaturated fatty acid Phosphate PHO OH O C R2 O β β α α α α O
  62. 62. 2-Lecithins:2-Lecithins: DefinitionDefinition: Lecithins areLecithins are glycerophospholipids that containglycerophospholipids that contain choline as a base beside phosphatidiccholine as a base beside phosphatidic acid. They exist in 2 formsacid. They exist in 2 forms αα- and- and ββ-- lecithins. Lecithins are a common celllecithins. Lecithins are a common cell constituent obtained from brain (constituent obtained from brain (αα-- type), egg yolk (type), egg yolk (ββ-type), or liver (both-type), or liver (both types). Lecithins are important in thetypes). Lecithins are important in the metabolism of fat by the liver.metabolism of fat by the liver. Structure:Structure: Glycerol is connected at C2 orGlycerol is connected at C2 or C3 with a polyunsaturated fatty acid, atC3 with a polyunsaturated fatty acid, at C1 with a saturated fatty acid, at C3 orC1 with a saturated fatty acid, at C3 or C2 by phosphate to which the cholineC2 by phosphate to which the choline base is connected. The common fattybase is connected. The common fatty acids in lecithins are stearic, palmitic,acids in lecithins are stearic, palmitic, oleic, linoleic, linolenic, clupandonic oroleic, linoleic, linolenic, clupandonic or arachidonic acids.arachidonic acids.
  63. 63. LysolecithinLysolecithin causes hemolysis of RBCs. Thiscauses hemolysis of RBCs. This partially explains toxic effect of snakepartially explains toxic effect of snake venom,. The venom containsvenom,. The venom contains lecithinaselecithinase,, which hydrolyzes the polyunsaturatedwhich hydrolyzes the polyunsaturated fatty converting lecithin into lysolecithin.fatty converting lecithin into lysolecithin. Lysolecithins are intermediates inLysolecithins are intermediates in metabolism of phospholipidsmetabolism of phospholipids. CH2 O C HO CH2 C C O P R1 R2 O O α-Lecithin O OH O CH2 O C H CH2 C O R1 O β-Lecithin P OH O C R2 O CH2 CH2 N CH3 CH3 CH3 + OCH2CH2N CH3 CH3 CH3 + Choline Choline O
  64. 64.  Lung surfactantLung surfactant  Is a complex of dipalmitoyl-lecithin,Is a complex of dipalmitoyl-lecithin, sphingomyelin and a group of apoproteinssphingomyelin and a group of apoproteins called apoprotein A, B, C, and D.called apoprotein A, B, C, and D.  It is produced by type II alveolar cells andIt is produced by type II alveolar cells and is anchored to the alveolar surface of typeis anchored to the alveolar surface of type II and I cells.II and I cells.  It lowers alveolar surface tension andIt lowers alveolar surface tension and improves gas exchange besides activatingimproves gas exchange besides activating macrophages to kill pathogens.macrophages to kill pathogens.  In premature babies, this surfactant isIn premature babies, this surfactant is deficient and they suffer fromdeficient and they suffer from respiratoryrespiratory distress syndromedistress syndrome..  Glucocorticoids increase the synthesis ofGlucocorticoids increase the synthesis of the surfactant complex and promotethe surfactant complex and promote differentiation of lung cells.differentiation of lung cells.
  65. 65. 3-Cephalins (or Kephalins):3-Cephalins (or Kephalins): DefinitionDefinition: They are phosphatidyl-They are phosphatidyl- ethanolamine or serine. Cephalinsethanolamine or serine. Cephalins occur in association with lecithins inoccur in association with lecithins in tissues and are isolated from thetissues and are isolated from the brain (brain (Kephale = head).Kephale = head). StructureStructure: Cephalins resemble: Cephalins resemble lecithins in structure except thatlecithins in structure except that choline is replaced by ethanolamine,choline is replaced by ethanolamine, serine or threonine amino acids.serine or threonine amino acids.
  66. 66. Certain cephalins are constituents of theCertain cephalins are constituents of the complex mixture of phospholipids,complex mixture of phospholipids, cholesterol and fat that constitute the lipidcholesterol and fat that constitute the lipid component of the lipoproteincomponent of the lipoprotein ““thromboplastinthromboplastin” which accelerates the” which accelerates the clotting of blood by activation ofclotting of blood by activation of prothrombin to thrombin in presence ofprothrombin to thrombin in presence of calcium ionscalcium ions. CH2 O C HO CH2 C C O P R1 R2 O O α-Cephalin O OH O CH2 CH2 NH2 Ethanolamine HO CH2 CH COOH Serine NH2 HO CH CH COOH Threonine NH2CH3
  67. 67. 4-Plasmalogens:4-Plasmalogens: Definition:Definition: Plasmalogens are found inPlasmalogens are found in the cell membrane phospholipidsthe cell membrane phospholipids fraction of brain and muscle (10% offraction of brain and muscle (10% of it is plasmalogens), liver, semen andit is plasmalogens), liver, semen and eggs.eggs. StructureStructure: Plasmalogens resemblePlasmalogens resemble lecithins and cephalins in structurelecithins and cephalins in structure but differ in the presence ofbut differ in the presence of αα,,ββ-- unsaturated fatty alcoholunsaturated fatty alcohol rather thanrather than a fatty acid at C1 of the glycerola fatty acid at C1 of the glycerol connected by ether bond.connected by ether bond.  At C2 there is an unsaturated long-At C2 there is an unsaturated long- chain fatty acid, however, it may be achain fatty acid, however, it may be a very short-chain fatty acidvery short-chain fatty acid
  68. 68. Properties: Similar to lecithinsSimilar to lecithins. CH2 C HO CH2 C O P R2 O α-Plasmalogen O OH O CH2 CH2 N CH3 CH3 CH3 + α,β-Unsaturated fatty alcoholCH CH R1O
  69. 69. 5-Inositides5-Inositides:  DefinitionDefinition:: - They are phosphatidyl inositol.They are phosphatidyl inositol.  StructureStructure: They are similar to lecithins orThey are similar to lecithins or cephalins but they have the cyclic sugarcephalins but they have the cyclic sugar alcohol,alcohol, inositolinositol as the base. They areas the base. They are formed of glycerol, one saturated fatty acid,formed of glycerol, one saturated fatty acid, one unsaturated fatty acid, phosphoric acidone unsaturated fatty acid, phosphoric acid and inositoland inositol CH2 C HO CH2 C O P R2 O α-Phosphatidylinositol O OH O C R1O O H H OH OH HOH H OHOH H H 1 2 3 4 56
  70. 70. SourceSource: Brain tissuesBrain tissues. FunctionFunction: Phosphatidyl inositol is a majorPhosphatidyl inositol is a major component of cell membranecomponent of cell membrane phospholipids particularly at the innerphospholipids particularly at the inner leaflet of it.leaflet of it.  They play a major role as secondThey play a major role as second messengers during signalmessengers during signal transduction for certain hormone..transduction for certain hormone.. On hydrolysis by phospholipase C,On hydrolysis by phospholipase C, phosphatidyl-inositol-4,5-diphosphatephosphatidyl-inositol-4,5-diphosphate producesproduces diacyl-glycerol and inositol-diacyl-glycerol and inositol- triphosphatetriphosphate both act to liberateboth act to liberate calcium from its intracellular stores tocalcium from its intracellular stores to mediate the hormone effects.mediate the hormone effects.
  71. 71. 6-Cardiolipins:6-Cardiolipins: DefinitionDefinition: They are diphosphatidyl-They are diphosphatidyl- glycerol. They are found in the innerglycerol. They are found in the inner membrane of mitochondria initially isolatedmembrane of mitochondria initially isolated from heart muscle (cardio). It is formed of 3from heart muscle (cardio). It is formed of 3 molecules of glycerol, 4 fatty acids and 2molecules of glycerol, 4 fatty acids and 2 phosphate groupsphosphate groups.. FunctionFunction:: Used in serological diagnosis ofUsed in serological diagnosis of autoimmunity diseases.autoimmunity diseases. CH2 C HO CH2 C O P R2 O Cardiolipin O OH O C R1O O CH2 CH OH CH2 CH2 CH O CH2 C OP R3 O O OH O CR4 O O
  72. 72. B-SphingophospholipidsB-Sphingophospholipids 1-Sphingomyelins1-Sphingomyelins  Definition:Definition: Sphingomyelins are found inSphingomyelins are found in large amounts in brain and nerves and inlarge amounts in brain and nerves and in smaller amounts in lung, spleen, kidney,smaller amounts in lung, spleen, kidney, liver and bloodliver and blood.  Structure:Structure: Sphingomyelins differ fromSphingomyelins differ from lecithins and cephalins in that they containlecithins and cephalins in that they contain sphingosine as the alcohol instead ofsphingosine as the alcohol instead of glycerol, they contain two nitrogenousglycerol, they contain two nitrogenous bases: sphingosine itself and choline.bases: sphingosine itself and choline.  Thus, sphingomyelins contain sphingosineThus, sphingomyelins contain sphingosine base, one long-chain fatty acid, choline andbase, one long-chain fatty acid, choline and phosphoric acid.phosphoric acid.  To the amino group of sphingosine the fattyTo the amino group of sphingosine the fatty acid is attached by an amide linkage.acid is attached by an amide linkage.
  73. 73. Ceramide This part of sphingomyelin inThis part of sphingomyelin in which the amino group of sphingosine iswhich the amino group of sphingosine is attached to the fatty acid by an amideattached to the fatty acid by an amide linkage.linkage.  Ceramides have been found in the free stateCeramides have been found in the free state in the spleen, liver and red cells.in the spleen, liver and red cells. CH CH NH CH2 CHCH(CH2)12CH3 OH Sphingosine C R1 O O P O OH O CH2 CH2 N CH3 CH3 CH3 + Choline Fatty acid Phosphate Ceramide Sphingomyelin
  74. 74. B-GlycolipidsB-Glycolipids  DefinitionDefinition: They are lipids that containThey are lipids that contain carbohydrate residues with sphingosinecarbohydrate residues with sphingosine as the alcohol and a very long-chain fattyas the alcohol and a very long-chain fatty acid (24 carbon series).acid (24 carbon series).  They are present in cerebral tissue,They are present in cerebral tissue, therefore are calledtherefore are called cerebrosidescerebrosides  ClassificationClassification: According to the numberAccording to the number and nature of the carbohydrate residue(s)and nature of the carbohydrate residue(s) present in the glycolipids the following arepresent in the glycolipids the following are 1. Cerebrosides. They have one galactoseThey have one galactose molecule (galactosides).molecule (galactosides). 2. Sulfatides. They are cerebrosides withThey are cerebrosides with sulfate on the sugar (sulfatedsulfate on the sugar (sulfated cerebrosides).cerebrosides). 3. Gangliosides. They have several sugarThey have several sugar and sugaramine residues.and sugaramine residues.
  75. 75. 1-Cerebrosides:1-Cerebrosides:  Occurrence: They occur in myelin sheath of nerves and white matter of the brain tissues and cellular membranes. They are important for nerve conductance.  Structure: They contain sugar, usually β-galactose and may be glucose or lactose, sphingosine and fatty acid, but no phosphoric acid. CH CH NH CH2 CHCH(CH2)12CH3 OH Sphingosine C R1 O O Psychosin Fatty acid Ceramide Cerebroside OOH H H H OHH OH CH2OH H Galactose
  76. 76. 3-Gangliosides:3-Gangliosides:  They are more complex glycolipids thatThey are more complex glycolipids that occur in the gray matter of the brain,occur in the gray matter of the brain, ganglion cells, and RBCs. They transferganglion cells, and RBCs. They transfer biogenic amines across the cell membranebiogenic amines across the cell membrane and act as a cell membrane receptor.and act as a cell membrane receptor.  GangliosidesGangliosides containcontain sialic acid (N-sialic acid (N- acetylneuraminicacetylneuraminic acid),acid), ceramideceramide (sphingosine + fatty acid of 18-24 carbon(sphingosine + fatty acid of 18-24 carbon atom length), 3 molecules of hexoses (1atom length), 3 molecules of hexoses (1 glucose + 2 galactose) and hexosamine. Theglucose + 2 galactose) and hexosamine. The most simple type of it themost simple type of it the monosialoganglioside,. It works as amonosialoganglioside,. It works as a receptor for cholera toxin in the humanreceptor for cholera toxin in the human intestine.intestine. Ceramide-Glucose-Galactose-N-acetylgalactosamine-Galactose Monosialoganglioside Sialic acid
  77. 77. C-LipoproteinsC-Lipoproteins  DefinitionDefinition: Lipoproteins are lipids combinedLipoproteins are lipids combined with proteins in the tissues. The lipidwith proteins in the tissues. The lipid component is phospholipid, cholesterol orcomponent is phospholipid, cholesterol or triglycerides. The holding bonds aretriglycerides. The holding bonds are secondary bonds.secondary bonds.  They include:They include: 1.1. Structural lipoproteinsStructural lipoproteins: These are widely: These are widely distributed in tissues being present indistributed in tissues being present in cellular and subcellular membranes. In lungcellular and subcellular membranes. In lung tissues acting as a surfactant in a complextissues acting as a surfactant in a complex of a protein and lecithin. In the eye,of a protein and lecithin. In the eye, rhodopsin of rods is a lipoprotein complex.rhodopsin of rods is a lipoprotein complex.  Transport lipoproteinsTransport lipoproteins::  These are the forms present in bloodThese are the forms present in blood plasma. They are composed of a proteinplasma. They are composed of a protein calledcalled apolipoproteinapolipoprotein and different types ofand different types of lipids. (Cholesterol, cholesterol esters,lipids. (Cholesterol, cholesterol esters, phospholipids and triglycerides). As thephospholipids and triglycerides). As the lipid content increases, the density oflipid content increases, the density of plasma lipoproteins decreasesplasma lipoproteins decreases
  78. 78.  Plasma lipoproteins can be separated byPlasma lipoproteins can be separated by two methodstwo methods: 1.1. Ultra-centrifugationUltra-centrifugation: Using the rate of: Using the rate of floatation in sodium chloride solutionfloatation in sodium chloride solution leading to their sequential separation intoleading to their sequential separation into chylomicronschylomicrons, very low density, very low density lipoproteins (lipoproteins (VLDL or pre-VLDL or pre-ββ-lipoproteins-lipoproteins),), low density lipoproteins (low density lipoproteins (LDL orLDL or ββ-- lipoproteinslipoproteins), high density lipoproteins), high density lipoproteins ((HDL orHDL or αα-lipoproteins-lipoproteins) and) and albumin-freealbumin-free fattyfatty acids complex.acids complex. 2.2. ElectrophoresisElectrophoresis:: is the migration ofis the migration of charged particles in an electric field eithercharged particles in an electric field either to the anode or to the cathode. Itto the anode or to the cathode. It sequentially separates the lipoproteinssequentially separates the lipoproteins intointo chylomicronschylomicrons,, pre-pre-ββ-,-, ββ-, and-, and αα-- lipoprotein andlipoprotein and albumin-free fattyalbumin-free fatty acidsacids complexcomplex. Polar lipids (phospholipids) Nonpolar lipids (cholesterol and its esters and triacylglycerols) Structure of a plasma lipoprotein complex Polar apolipoproteins
  79. 79. a) Chylomicronsa) Chylomicrons: They have the largestThey have the largest diameter and the least density. They containdiameter and the least density. They contain 1-1- 2% protein2% protein only andonly and 98-99% fat98-99% fat. The main lipid. The main lipid fraction is triglycerides absorbed from thefraction is triglycerides absorbed from the intestine and they containintestine and they contain small amountssmall amounts of theof the absorbed cholesterol and phospholipids.absorbed cholesterol and phospholipids. b) Very low-density lipoproteins (VLDL) orb) Very low-density lipoproteins (VLDL) or pre-pre-ββ-lipoproteins-lipoproteins: Their diameter is smallerTheir diameter is smaller than chylomicrons. They contain aboutthan chylomicrons. They contain about 7-10%7-10% proteinprotein andand 90-93% lipid90-93% lipid. The lipid content is. The lipid content is mainly triglycerides formed in the liver. Theymainly triglycerides formed in the liver. They contain phospholipid and cholesterolcontain phospholipid and cholesterol more thanmore than chylomicrons.chylomicrons. c) Low-density lipoproteins (LDL) or) Low-density lipoproteins (LDL) or ββ-- lipoproteinslipoproteins: They containThey contain 10-20% proteins10-20% proteins inin the form of apolipoprotein B. Theirthe form of apolipoprotein B. Their lipidlipid content varies from 80-90%.content varies from 80-90%. They contain aboutThey contain about 60% of total blood cholesterol and 40% of total60% of total blood cholesterol and 40% of total blood phospholipids. As their percentageblood phospholipids. As their percentage increases, the liability to atherosclerosisincreases, the liability to atherosclerosis increases.increases.
  80. 80. d) High-density lipoproteins (HDL) ord) High-density lipoproteins (HDL) or αα-- LipoproteinsLipoproteins: They containThey contain 35-55%35-55% proteinsproteins in the form of apolipoprotein A.in the form of apolipoprotein A. They containThey contain 45-65% lipids45-65% lipids formed offormed of cholesterol (cholesterol (40% of40% of total blood contenttotal blood content)) and phospholipids (and phospholipids (60%60% of total bloodof total blood contentcontent). They act as cholesterol). They act as cholesterol scavengersscavengers, as their percentage, as their percentage increases, the liability to atherosclerosisincreases, the liability to atherosclerosis decreases. They are higher in femalesdecreases. They are higher in females than in males. Due to their high proteinthan in males. Due to their high protein content they possess the highestcontent they possess the highest density.density. e) Albumin-free fatty acids complex:e) Albumin-free fatty acids complex: It isIt is a proteolipid complex witha proteolipid complex with 99% protein99% protein content associated with long-chain freecontent associated with long-chain free fatty acids for transporting them.fatty acids for transporting them.
  81. 81. Cholesterol:Cholesterol: Importance:Importance: --  It is the most important sterol in animalIt is the most important sterol in animal tissues astissues as free alcoholfree alcohol or in an esterifiedor in an esterified form (form (with linoleicwith linoleic,, oleic, palmitic acids oroleic, palmitic acids or other fatty acidsother fatty acids).).  Steroid hormones, bile salts and vitamin DSteroid hormones, bile salts and vitamin D are derivatives from it.are derivatives from it.  Tissues contain different amounts of it thatTissues contain different amounts of it that serve a structural and metabolic role, e.g.,serve a structural and metabolic role, e.g., adrenal cortexadrenal cortex content is 10%,content is 10%, whereas,whereas, brain is 2%,brain is 2%, others 0.2-0.3%.others 0.2-0.3%. SourceSource:: - It is synthesized in the body fromIt is synthesized in the body from acetyl-CoA (1gm/day, cholesterol does notacetyl-CoA (1gm/day, cholesterol does not exist in plants) and is also taken in the dietexist in plants) and is also taken in the diet ((0.3 gm/day as in, butter, milk, egg yolk,0.3 gm/day as in, butter, milk, egg yolk, brain, meat and animal fat).brain, meat and animal fat).
  82. 82. Physical propeties:Physical propeties:It has a hydroxyl group on C3, a double bond between C5 and C6, 8 asymmetric carbon atoms and a side chain of 8 carbon atoms. It is found in all animal cells, corpus luteum and adrenal cortex, human brain (17% of the solids). In the blood (the total cholesterol amounts about 200 mg/dL of which 2/3 is esterified, chiefly to unsaturated fatty acids while the remainder occurs as the free cholesterol. CH3 CH3 HO CH3 CH3 CH3 Cholesterol
  83. 83. Chemical propertiesChemical properties Intestinal bacteriaIntestinal bacteria reduce cholesterol intoreduce cholesterol into coprosterol andcoprosterol and dihydrocholesteroldihydrocholesterol.. - It is also oxidized into- It is also oxidized into 7-7- DehydrocholesterolDehydrocholesterol and further unsaturatedand further unsaturated cholesterol with a second double bondcholesterol with a second double bond betweenbetween C7 and C8.C7 and C8. When the skin isWhen the skin is irradiated with ultraviolet light 7-irradiated with ultraviolet light 7- dehydrocholesterol is converted to vitamindehydrocholesterol is converted to vitamin D3.D3. This explains the value of sun light inThis explains the value of sun light in preventingpreventing ricketsrickets.. CH3 CH3 HO CH3 CH3 CH3 Coprosterol, in feces H CH3 CH3 HO CH3 CH3 CH3 Dihydrocholesterol, in blood and other tissues H
  84. 84. ErgosterolErgosterol differs from 7-differs from 7- dehydrocholesterol in the side chain.dehydrocholesterol in the side chain. Ergosterol is converted to vitamin D2 byErgosterol is converted to vitamin D2 by irradiation with UV Ergosterol and 7-irradiation with UV Ergosterol and 7- dehydrocholesterol are called Pro-vitaminsdehydrocholesterol are called Pro-vitamins D or precursors of vitamin D.D or precursors of vitamin D.  - It was first isolated from ergot, a fungus- It was first isolated from ergot, a fungus then from yeast. Ergosterol is less stablethen from yeast. Ergosterol is less stable than cholesterol (than cholesterol (because of having 3because of having 3 double bondsdouble bonds).). CH3 CH3 HO CH3 CH3 CH3 7-dehydrocholesterol CH3 CH3 HO CH3 CH3 CH3 Ergosterol CH3
  85. 85. SteroidsSteroids  Steroids constitute an importantSteroids constitute an important class of biological compounds.class of biological compounds.  Steroids are usually found inSteroids are usually found in association with fat. They can beassociation with fat. They can be separated from fats afterseparated from fats after saponification since they occur in thesaponification since they occur in the unsaponifiable residue.unsaponifiable residue.  They areThey are derivatives of cholesterolderivatives of cholesterol that is formed of steroid ring orthat is formed of steroid ring or nucleus.nucleus.  Biologically important groups ofBiologically important groups of substances, which contain this ring, are:substances, which contain this ring, are: 1.1. Sterols.Sterols. 2.2. Adrenal cortical hormones.Adrenal cortical hormones. 3.3. Male and female sex hormones.Male and female sex hormones. 4.4. Vitamin D group.Vitamin D group. 5.5. Bile acids.Bile acids. 6.6. Cardiac glycosides.Cardiac glycosides.
  86. 86.  General consideration about naturally occurringGeneral consideration about naturally occurring steroidssteroids: A typical member of this groupA typical member of this group is cholesterolis cholesterol.. Certain facts have to be considered when drawingCertain facts have to be considered when drawing steroid formulasteroid formula: 1) There is always oxygen in the form of1) There is always oxygen in the form of hydroxyl orhydroxyl or ketone on C3ketone on C3.. 2) Rings2) Rings C and D are saturatedC and D are saturated (stable).(stable). 3) Methyl groups at3) Methyl groups at C18 C19C18 C19. In case of vitamin D,. In case of vitamin D, the CH3the CH3 group at C19 becomes a methylene groupgroup at C19 becomes a methylene group (=CH2) and the ring B is opened, whereas,(=CH2) and the ring B is opened, whereas, thisthis methyl group is absent in female sex hormonesmethyl group is absent in female sex hormones (estrogens).(estrogens). 4) In estrogens (female sex hormones) ring A is4) In estrogens (female sex hormones) ring A is aromatic and there isaromatic and there is no methyl group on C10.no methyl group on C10. CH3 CH3 HO Steroid ring 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1617 18 19 A B C D
  87. 87. Bile acidsBile acids:  They are produced from oxidation ofThey are produced from oxidation of cholesterol in the liver producingcholesterol in the liver producing cholic andcholic and chenodeoxycholic acidschenodeoxycholic acids that are conjugatedthat are conjugated withwith glycine or taurineglycine or taurine to produceto produce glycocholic,glycocholic, glycochenodeoxycholic,glycochenodeoxycholic, taurocholictaurocholic and taurochenodeoxycholicand taurochenodeoxycholic acids. They react with sodium or potassiumacids. They react with sodium or potassium to produceto produce sodiumsodium oror potassium bile saltspotassium bile salts..  Their function is as followsTheir function is as follows: 1.1.Emulsification of lipids during digestion.Emulsification of lipids during digestion. 2.2.Help in digestion of the other foodstuffs.Help in digestion of the other foodstuffs. 3.3.Activation of pancreatic lipase.Activation of pancreatic lipase. 4.4.Help digestion and absorption of fat-solubleHelp digestion and absorption of fat-soluble vitamins.vitamins. 5.5.Solubilizing cholesterol in bile and preventSolubilizing cholesterol in bile and prevent gall stone formation.gall stone formation. 6.6.Choleretic action (stimulate their ownCholeretic action (stimulate their own secretion).secretion). 7.7.Intestinal antiseptic that preventIntestinal antiseptic that prevent putrefactionputrefaction
  88. 88. CH3 CH3 HO CH3 C Sodium-tauro or glyco-cholate CH3 CH3 HO CH3 C Sodium-tauro or glyco-chenodeoxycholate OH OH OH O O R1 or R2 R1 or R2 (CH2)2 SO3 -Na+H2NCH2 COO-Na+H2N Sodium taurateSodium glycate R1 R2

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