LIPIDS OF PHYSIOLOGICAL SIGNIFICANCE

1. LIPIDS OF PHYSIOLOGICAL SIGNIFICANCE

2. Definition: • Lipids may be regarded as organic substances relatively insoluble in water, soluble in organic solvents (alcohol, ether etc.) actually or potentially related to fatty acids and utilized by the living cells.

3. Lipids in foods and in the human body fall into three classes • Triglycerides • ≈95% of all lipids • Phospholipids • Sterols

4. Fat (triglycerides) • Body’s chief storage form for the energy* Body’s ability to store glycogen is limited • Relative to carbohydrate, much more fat can be stored in a small space • Gram for gram, fats provide more than 2x the energy of carbohydrate - making fat an efficient storage form of energy

5. Inside the human body, some cells are specialized for fat storage*. • These fat cells seem to expand indefinitely • The more fat they store, the larger they grow. Adipocyte

6. Functions: • Energy: concentrated fuel reserve • Thermal Insulator • Structural component of Biomembranes e.g. Phospholipids and Cholesterol • Metabolic Regulators e.g. Steroid hormones and Prostaglandins • Surfactants and emulsifying agents • Source of fat soluble vitamins • Adding taste and palatability to food

7. Clinical Applications: • Obesity • Atherosclerosis • Ketosis • Hyperlipidemias

8. CLASSIFICATION OF LIPIDS • Simple lipids: esters of fatty acid with alcohol e.g. fat, waxes, TG • Compound lipids: esters of fatty acid with alcohol with additional groups such as phosphate, carbohydrate, protein etc. e.g. phospholipids, sulpholipids, glycolipids and lipoprotein • Derived lipids: e.g. fatty acids, glycerol, lipid soluble vitamin, steroids, prostaglandins etc.

9. FATTY ACIDS: • carboxylic acids with hydrocarbon side chain O  R  C  OH • Numbering of carbon atoms: odd & even • Position of double bonds: S & US

10. Types of Fatty Acids: • Depending on: • Length of hydrocarbon chain: short chain and long chain FA • Presence of double bond: SFA, UFA & PUFA • Nutritional requirement: EFA & NEFA

11. Essential fatty acids • Linoleic acid • Linolenic acid • Arachidonic acid

12. Saturated versus Unsaturated Fatty Acids Triglycerides: Fatty acids and glycerol Fatty acids can be saturated or unsaturated

13. Contains one double bond Contains more than one double bond

14. Degree of saturation • In general, the more saturated the fatty acids, the firmer the fat is at room temperature* • Fats with shorter-chain fatty acids or unsaturated ones are softer and melt more readily at lower temperatures

15. Saturated vs. Unsaturated Fats • Animal fats are mostly saturated • Most plant and fish oils are rich in unsaturated fats • Diet with high saturated fats are linked to cardiovascular diseases

17. Saturated versus Unsaturated Fatty Acids • Olive oil • Evidence from Mediterranean regions suggests that olive oil confers a degree of protection against heart disease when it is used in place of other fats

18. Phospholipids • Phospholipids = 2 fatty acids + glycerol + a phosphorus-containing molecule • A component of cell membrane

19. TRIACYLGLYCEROL: • O •  • O CH2  O  C  R1 •  R2  C  O  CH O •  • CH2  O  C  R2

20. Hydrolysis Lipase Lipase Lipase TG--------- DG----------MG----------Glycerol H2O FA H2O FA H2O FA

21. COMPOUND LIPIDS • Phospholipids: • FA + alcohol + Phosphoric acid • O •  • O CH2 – O – C – R1 •  • R2 – C – O – CH •  • CH2 – group

22. Phosphatidic acid: • O •  • O CH2 – O – C – R1 •  • R2 – C – O – CH •  • CH2- group

23. Phosphatidyl choline or Lecithin • O •  • O CH2 – O – C – R1 •  • R2 – C – O – CH •  • CH2- grp • Surfactant of lung • Amniotic fluid - 0.100 mg/dl – fetal lung maturity

24. Phosphatidylethanolamine (cephalin) • CH2 – CH2 NH3 (ethanolamine) as a group • Phosphatidyl inositol: • Biomembrane • Diacylglycerol and inositol triphosphate (second messengers) • Plasmalogens: • Brain, biomembrane and muscles

25. Sphingomyelins: • FA + Phosphoric acid + choline + amino alcohol (sphingosine) • found in brain and nerve tissue • Glycosphingolipids (glycolipids) • Brain, plasma membrane e.g. Galactosylceramide, Glucosylceramine Gangliosides

26. Functions of Phospholipids: • Structural component e.g. Cell membrane • Role in enzyme action: mitochondrial enzyme system • Blood Coagulation: Prothrombin------Thrombin • Lipid absorption in intestine • Transport of lipids from intestine • Transport of lipids from liver • Electron transport • Membrane phospholipids as source of arachidonic acid • Insulation • Second messenger – phosphatidyl inositol

27. DERIVED LIPIDS: • Cholesterol: • Biomembrane, Nerve tissue, Adrenocortical hormones, sex hormone, Vitamin D and Bile acids • Structure:Cyclopentanoperhydrophenanthrene ring • Vitamin D: UV • Cholesterol------------7 dehydro cholesterol ---- ---- Calcitriol (Vitamin D)

28. Sterols (Steroids) • Large, complicated molecules consisting of connected rings of carbon atoms with side chains of carbon, hydrogen, and oxygen

29. Steroids

31. Steroids • Cholesterol • Synthesized in the liver • Gives strength to cell membranes • In myelin sheath, bile salts, vitamin D produced by the skin • Excess in body leads to gall stones and plaque in the arteries

32. Cholesterol is the major representative of Sterols It serves as • Membrane component • Precursor for making bile • Precursor for making steroid hormones • Vitamin D and sex hormones are also sterols

33. Cholesterol can be obtained from diet and can be made by the body • Not an essential nutrient • Cholesterol forms the major parts of the plaques that narrow arteries in atherosclerosis • The underlying cause of heart attacks and strokes

34. Cholesterol Plaque

35. Hypercholesterolemia • Can be the result of high cholesterol or high calorie diet • Can also be caused by poor transportation and clearance mechanisms

36. Steroids…. • Bile salts • Synthesized from cholesterol in the liver • Sent to the digestive tract to emulsify fats • Promotes absorption of cholesterol in the digestive tract • Fat-soluble vitamins: A, D, E, K • A for night vision • D promotes absorption of Ca+ in intestinal tract and deposition of Ca+ in the bones • E prevents oxidation of unsaturated fatty acids in cell membranes • K functions in blood cloting

37. Steroids… • Hormones: • Sex hormones control reproduction, sexual characteristics, and general growth • Adrenal corticosteroids • Cortisone increases blood glucose levels and reduces inflammation • Aldosterone acts in the kidneys to maintain Na+ and water balance • Sex hormones • Anabolic steroid, derivative of testosterone • Prevents breakdown of worn out muscle cells • Has dangerous side effects

38. A Lipoprotein

39. Lipoproteins • transporter proteins for lipids • Major Lipoproteins: VLDL, LDL, HDL

40. LIPOPROTEINS: • They are molecular complexes of lipids and specific proteins called apolipoproteins. They function as transport vehicles for lipids in blood plasma. • Consists of a neutral lipid core surrounded by a coat shell of phospholipids, apoproteins & cholesterol. Classification:According toDensity or Electrophoretic mobility: • Chylomicron: ↑size↓density • VLDL (Pre  Lp) • IDL (broad  Lp) • LDL ( Lp) • HDL ( Lp): ↑ density ↓size

41. Functions: • Chylomicron: Transport, dietary TG, adipose tissue, muscle and heart • VLDL: Carriers of endogenous TG • LDL: Liver  peripheral tissue • HDL: Peripheral tissue  liver

42. Chemical Properties of Triacylglycerols The chemical reactions of triacylglycerols are similar to those of alkenes and esters. • In hydrogenation, double bonds in unsaturated fatty acids react with H2 in the presences of Ni or Pt catalyst. • In hydrolysis, ester bonds are split by water in the presence of an acid, a base, or an enzyme.

43. Hydrogenation of Oils Hydrogenation: • Adds hydrogen to double bonds in oils to form single bonds. • Produces solid shortening, margarine, and other products.

44. Hydrogenation • Hydrogenation converts double bonds to single bonds.

45. Hydrolysis • In hydrolysis, triacylglycerols are split into glycerol and three fatty acids. • An acid or enzyme catalyst is required.

46. Saponification and Soap Soaps are: • Salts of fatty acids. • Formed by saponification, a reaction in which a triacylglycerol reacts with a strong base.