Chapter04 3102020 1 What are Lipids The lipids constitute a very important heterogeneous group of organic substances in plant and animal tissues and related either actually or potentially to the fatty acids ID: 1044118
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1. Chemistry of Lipids and their Biomedical ImportanceChapter-043/10/20201
2. What are Lipids?The lipids constitute a very important heterogeneous group of organic substances in plant and animal tissues, and related either actually or potentially to the fatty acids. Chemically they are various types of esters of different alcohols. In addition to alcohol and fatty acids, some of the lipids may contain phosphoric acid, nitrogenous base and carbohydrates. 3/10/20202
3. Bloor’s CriteriaAccording to Bloor, lipids are compounds having the following characteristics: • They are insoluble in water. • Solubility in one or more organic solvents, such as ether, chloroform, benzene, acetone, etc, so called fat solvents. • Some relationship to the fatty acids as esters either actual or potential. • Possibility of utilization by living organisms. 3/10/20203
4. Thus, lipids include fats, oils, waxes and related compounds. An oil is a lipid which is liquid at ordinary temperature. Distinction between fats and oils is a purely physical one.Chemically they are all esters of glycerol with higher fatty acids.3/10/20204
5. Polyunsaturated (Polyethenoid)fatty acids:There are three polyunsaturated fatty acids of biological importance. Linoleic acid series (18 : 2; 9, 12) It contains two double bonds between C9 and C10; and between C12 and C13. Their general formula is CnH2n–3 COOH. Dietary sources: Linoleic acid is present in sufficient amounts in peanut oil, corn oil, cottonseed oil, soyabean oil and egg yolk.3/10/20205
6. https://www.google.com/search?q=Linolenic+acid+series+%2818+:+3;+9,+12,+15%29&tbm=isch&chips=q:Linolenic+acid+series+%2818+:+3;+9,+12,+15%29,online_chips:lipids&rlz=1C1CHBD_enPK777PK777&hl=en&ved=2ahUKEwiTnNjGi4voAhXr1-AKHfWuCR8Q4lYoA3oECAEQGA&biw=1263&bih=640#imgrc=e-Pu4OS4EQphsM3/10/20206
7. Linolenic acid series (18 : 3; 9, 12, 15)It contains three double bonds between 9 and 10; 12 and 13; and 15 and 16. Their general formula is CnH2n–5 COOH.Dietary Source: Found frequently with linoleic acid, but particularly present in linseed oil, rapeseed oil, soybean oil, fish visceras and liver oil (cod liver oil).3/10/20207
8. https://www.google.com/search?q=Linolenic+acid+series+%2818+:+3;+9,+12,+15%29&tbm=isch&chips=q:Linolenic+acid+series+%2818+:+3;+9,+12,+15%29,online_chips:lipids&rlz=1C1CHBD_enPK777PK777&hl=en&ved=2ahUKEwiTnNjGi4voAhXr1-AKHfWuCR8Q4lYoA3oECAEQGA&biw=1263&bih=640#imgrc=e-Pu4OS4EQphsM3/10/20208
9. Arachidonic acid series (20 : 4; 5, 8, 11, 14)It contains four double bonds. Their general formula: CnH2n–7 COOH Dietary source: Found in small quantities with linoleic acid and linolenic acid but particularly found in peanut oil. Also found in animal fats including Liver fats.3/10/20209
10. https://www.google.com/search?q=Arachidonic+acid+series+(20+%3A+4%3B+5%2C+8%2C+11%2C+14)&tbm=isch&ved=2ahUKEwjB3sGNjIvoAhVCweAKHXZJDDQQ2-cCegQIABAA&oq=Arachidonic+acid+series+(20+%3A+4%3B+5%2C+8%2C+11%2C+14)&gs_l=img.3...126618.131866..132573...1.0..0.534.780.2-1j5-1......0....1..gws-wiz-img.mvgcpWys2r0&ei=_gFlXsHnKcKCgwf2krGgAw&bih=640&biw=1263&rlz=1C1CHBD_enPK777PK777&hl=en#imgrc=pcZe6yH8Md_qDM3/10/202010
11. Functions of EFA: (Biomedical Importance)Structural elements of tissues: Polyunsaturated fatty acids occur in higher concentration in lipids associated with structural elements of tissues. Synthesis of prostaglandins and other compounds: Prostaglandins are synthesised from Arachidonic acid by cyclooxygenase enzyme system.Leukotrienes are conjugated trienes formed from arachidonic acid in leucocytes by the Lipoxygenase pathway. 3/10/202011
12. What is the difference between lymphocytes and monocytes?Monocytes are large, spherical cells that make up 2 to 8% of circulating WBCs.Monocytes can enter peripheral tissues to become tissue macrophages which can engulf large particles and pathogens. Lymphocytes , slightly larger than RBCs, make up 20 to 30% of circulating WBCs. They migrate in and out of the blood3/10/202012
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15. • Structural element of mitochondrial membrane: A deficiency of EFA causes swelling of mitochondrial membrane and reduction in efficiency of oxidative phosphorylation. This may explain for increased heat production noted in EFA deficient animals.3/10/202015
16. Serum level of cholesterolFats with high content of polyunsaturated fatty acids tends to lower serum level of cholesterol. Effect on clotting time: Prolongation of clotting time is noted in ingestion of fats rich in EFA.3/10/202016
17. Effect on fibrinolytic activityAn increase in fibrinolytic activity follows the ingestion of fats rich in EFA. Role of EFA in fatty liver: Deficiency of EFA produces fatty liver3/10/202017
18. • Role in visionDocosahexaenoic acid (22:6n-3) is the most abundant polyenoic fatty acids present in retinal photoreceptor membranes.Docosahexaenoic acid is formed from dietary linolenic acid. It enhances the electrical response of the photoreceptors to illumination. Hence linolenic acid is necessary in the diet for optimal vision.3/10/202018
19. CLINICAL ASPECTHuman deficiency: Some cases of Eczema like dermatitis, Degenerative changes in arterial wall and Fatty liver in man may be due to EFA deficiency. There are also some reports that administration of EFA in such cases may produce: – Some improvement of eczema in children kept on skimmed milk, – Prevent fatty liver (some cases) – Lowering of cholesterol levels. Infants and babies with low fat diet develop typical skin lesions which has shown to be improved with EFA (linoleic acid).3/10/202019
20. Docosahexaenoic acid: DHA (W3, 22:6)Docosahexaenoic acid (DHA) is a polyunsaturated fatty acid which is synthesized from α-linolenic or obtained directly from dietary fish oil. This fatty acid is present in high concentrations in retina, cerebral cortex, tastes and sperms. DHA is particularly needed for development of the brain and retina and is supplied via the placenta and milk. 3/10/202020
21. In EFA deficiency, nonessential polyenoic acids of the W9 family replace the essential fatty acids in phospholipids (PL), other complex lipids and membranes. Clinical Aspect Low blood levels of DHA have been reported in patients with Retinitis Pigmentosa3/10/202021
22. ALCOHOLSAlcohols contained in the lipid molecule includes glycerol, cholesterol and the higher alcohols, e.g. Cetylalcohol, C16H33COOH (usually found in waxes). Glycerol: Glycerol is commonly called as “glycerin” it is the simplest trihydric alcohol as it contains three hydroxyl groups in the moleculeIt is colourless oily fluid with a sweetish taste. It is miscible with water and alcohol in all proportions but is almost insoluble in ether.3/11/202022
23. Cetylalcohol, C16H33COOHCetyl alcohol also known as hexadecan-1-ol and palmityl alcohol, is a fatty alcohol with the formula CH3(CH2)15OH. At room temperature, cetyl alcohol takes the form of a waxy white solid or flakes. The name cetyl derives from the whale oil (Latin: cetus) from which it was first isolated.3/10/202023
24. Source IndustrialIt is obtained as a by-product of soap manufacture. It is also obtainable in the fermentation of glucose by changing conditions in such a way as to decrease the formation of CO2 and alcohol. 3/11/202024
25. PhysiologicalEndogenous source: Main source is from lipolysis of fats in adipose tissue. • Exogenous source: Dietary Approx. 22 per cent of glycerol directly absorbed to portal blood from the gut3/11/202025
26. Uses In medicineNitroglycerine is used as a vasodilator. • Glycerol therapy in cerebrovascular (CV) diseases reduces cerebral oedema3/11/202026
27. PhysiologicalIn body, glycerol has a definite nutritive value. It can be converted to glucose/and glycogen, the process called as gluconeogenesis3/11/202027
28. Steroids and Sterols1. The steroids are often found in association with fat. 2. They may be separated from the fat, after the fat is saponified, since they occur in unsaponifiable residue. 3. All of the steroids have a similar cyclic nucleus resembling phenanthrene (ring A, B and C) to which a cyclopentane ring (ring D) is attached. It is designated as cyclopentano perhydro-phenanthrene nucleus.3/11/202028
29. Methyl side chains occur typically at positions 10 and 13 (constituting carbon atoms 19 and 18 respectively). 5. A side chain at position 17 is usual. If the compound has one or more –OH groups and no carbonyl or carboxyl groups, it is called a ‘sterol’ and the name terminates in –”ol”. Most important sterol in human body is cholesterol.3/11/202029
30. https://www.google.com/search?q=cholesterol&rlz=1C1CHBD_enPK777PK777&hl=en&tbm=isch&source=iu&ictx=1&fir=CrakfnW6ATHbQM%253A%252CaHKglsYtHr8RdM%252C_&vet=1&usg=AI4_-kQoe2Lth9dZ7-510c6me5EtQx6sEA&sa=X&ved=2ahUKEwiT_YfM7pHoAhVJxYUKHUxtBCsQ_h0wAHoECAsQBA#imgrc=ZAGDAAZ4mbl5wM3/11/202030
31. Cholesterol StructureCholesterol is the most important sterol in human body. Its molecular formula is C27H45OH. It possesses “cyclo-pentane-perhydro-phenanthrene nucleus”. • It has an –OH group at C3. It has an unsaturated double bond between C5 and C6. It has two –CH3 groups at C10 and C13. It has an eight carbon side chain attached to C17.3/11/202031
32. https://www.google.com/search?q=cholesterol&tbm=isch&hl=en&chips=q:cholesterol,g_1:structure:MQG6dX6ktgo%3D&rlz=1C1CHBD_enPK777PK777&hl=en&ved=2ahUKEwjb9dDP7pHoAhWL2-AKHW3OCx8Q4lYoAXoECAEQFg&biw=1263&bih=689#imgrc=EDA39ean9m02DM3/11/202032
33. https://www.google.com/search?q=cholesterol+crystal&rlz=1C1CHBD_enPK777PK777&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjki735-5HoAhUO3IUKHUnIAOEQ_AUoAXoECA4QAw&biw=1264&bih=676#imgrc=U4YBiEkjyIDSrM Cholesterol crystals in Urine3/11/202033
34. https://www.google.com/search?q=cholesterol+crystal&tbm=isch&chips=q:cholesterol+crystal,g_1:atherosclerosis:uH3VJaL4QZg%3D&rlz=1C1CHBD_enPK777PK777&hl=en&ved=2ahUKEwj4nJP8-5HoAhXC1-AKHbPCATIQ4lYoAXoECAEQFg&biw=1247&bih=676#imgrc=Hd-vnRAOxu9loMBrain Cholesterols clefts3/11/202034
35. https://www.google.com/search?q=cholesterol+crystal&rlz=1C1CHBD_enPK777PK777&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjki735-5HoAhUO3IUKHUnIAOEQ_AUoAXoECA4QAw&biw=1264&bih=676#imgrc=rQMlZj0--FlMAMHistology of cholesterol crystals3/11/202035
36. OTHER STEROLS OF BIOLOGICAL IMPORTANCE 1. 7-Dehydrocholesterol It is an important sterol present in the skin. This differs from cholesterol only in having a second double bond, between C7 and C8 Source: In man, 7-dehydrocholesterol may be obtained partly by synthesis from cholesterol in skin and/or intestinal wall.https://www.google.com/search?q=7-Dehydrocholesterol&tbm=isch&ved=2ahUKEwjntbvk_pHoAhWy2OAKHbekBYYQ2-cCegQIABAA&oq=7-Dehydrocholesterol&gs_l=img.3..0i67j0l6j0i30l3.132217.132217..134439...0.0..0.238.238.2-1......0....1..gws-wiz-img.3KnoPgmMmw0&ei=jZ9oXqe7BrKxgwe3yZawCA&bih=676&biw=1247&rlz=1C1CHBD_enPK777PK777&hl=en#imgrc=39Z1wzBECCuTeM3/11/202036
37. Biomedical ImportanceIn the epidermis of skin, UV rays of sunshine change 7-dehydrocholesterol (pre-cholecalciferol) to cholecalciferol (vitamin D3). Hence 7-dehydrocholesterol is called as provitaminD3.This explains the value of sunshine in preventing rickets, a disease produced from vitamin D deficiency.3/11/202037
38. ErgosterolIt is a plant sterol, first isolated from ergot, a fungus of rye and later from yeast and certain mushrooms. Structurally this sterol has the same nucleus as 7-dehydrocholesterol but differs slightly in its side chainhttps://www.google.com/search?q=Ergosterol&tbm=isch&ved=2ahUKEwjflJ6l_5HoAhUF7eAKHZNPD1gQ2-cCegQIABAA&oq=Ergosterol&gs_l=img.3..0i67j0l9.275044.275044..275978...0.0..0.248.248.2-1......0....1..gws-wiz-img.4Ww67zPbpG4&ei=FKBoXt-6OYXagweTn73ABQ&bih=676&biw=1247&rlz=1C1CHBD_enPK777PK777&hl=en#imgrc=dBSgur_cW7QxxM&imgdii=KbzzQKgxv0nMhM3/11/202038
39. Biomedical ImportanceWhen irradiated with UV rays (long wave 265 μm) ergosterol is changed to vitamin D2 by the opening of the ring B of the sterol.Hence ergosterol is called as Provitamin-D2, over irradiation may produce toxic products3/11/202039
40. EmulsificationEmulsions of fat may be made by shaking vigorously in water and by emulsifying agents such as gums, soaps and proteins which produce more stable emulsions. Biomedical Importance of Emulsification The emulsification of dietary fats in intestinal canal, brought about by bile salts, is a prerequisite for digestion and absorption of fats3/11/202040
41. IDENTIFICATION OF FATS AND OILSSaponification Number Definition: The number of mgs of KOH required to saponify the free and combined FA in one gram of a given fat is called its saponification number.Acid Number Definition: Number of mgs of KOH required to neutralize the fatty acids in a gm of fat is known as the acid number.3/11/202041
42. Polenske Number Definition:It is the number of millilitre of 0.1 normal KOH required to neutralize the insoluble fatty acids (those not volatile with steam distillation) from 5 gram of fat.Reichert-Meissl Number Definition: It is the number of millilitres of 0.1 (N) alkali required to neutralize the soluble volatile fatty acids distilled from 5 gm of fat.Iodine Number Definition: Iodine number is defined as the number of grams of iodine absorbed by 100 gm of fat.3/11/202042
43. Clinical aspectFabry’s disease: An inherited disorder, a lipid storage disease (lipidosis). Inheritance: X-linked dominant, full symptoms only in males. • Enzyme deficiency: α-galactosidase. The enzyme is found normally in liver, spleen, kidney, brain and small intestine. 3/11/202043
44. Skin rash (reddish purple), Pain in lower extremities (painful neuropathy), Lipid accumulates in the endothelial lining of blood vessels, may produce vascular thrombosis. Progressive renal failure–due to extensive deposition of lipids in glomeruli. Occasionally manifestations of cardiac enlargement. Eye involvement: Corneal opacities, cataracts, vascular dilatation.3/11/202044
45. Krabbe’s Disease •An inherited disorder of lipid metabolism, a lipid storage disease(lipidosis) • Enzyme deficiency: Galacto-cerebrosidase (β-galactosidase). The enzyme normally catalyzes the hydrolysis of galactocerebrosides and it splits the linkage between ceramide and galactose • Nature of lipid accumulating: Galactosyl ceramide Clinical manifestations: – Severe mental retardation in infants – Total absence of myelin in central nervous system – Globoid bodies found in white matter of brain3/11/202045
46. https://www.google.com/search?q=myelin&rlz=1C1CHBD_enPK777PK777&tbm=isch&source=iu&ictx=1&fir=z_fEJ3sfazoa9M%253A%252CxjKaQrFZjm9iRM%252C_&vet=1&usg=AI4_-kSjyf2on2Ql_kxbHzkxPdIObaKeRg&sa=X&ved=2ahUKEwie147u05LoAhWjyIUKHaGhCwsQ_h0wAHoECAkQBA#imgrc=z_fEJ3sfazoa9M:3/11/202046
47. https://www.google.com/search?q=Globoid+bodies&rlz=1C1CHBD_enPK777PK777&hl=en&source=lnms&tbm=isch&sa=X&ved=2ahUKEwig6dD21JLoAhVIExoKHQGPAnkQ_AUoAXoECAsQAw&biw=1267&bih=621#imgrc=2I03XStHX_yaaM3/11/202047
48. Exercise on page 64 section 2MCQs are included in exam3/11/202048