Lipids and Membranes

1. Lipids and Membranes

2. Functions Of Lipids

3. Functions of Lipids • Source of energy • Cellular membranes • Excellent insulators • Thermal insulators • Electrical insulators (in membranes) • Special roles: • Signals • Hormones, Mediators, or growth factors. • Coenzymes • Vitamins

4. Lipids • Lipids:a heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties • insoluble in water, but soluble in nonpolar organic solvents including diethyl ether, chloroform, methylene chloride, and acetone • Amphipathic in nature • Lipids include • Open Chain forms • fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, glycolipids, • lipid-soluble vitamins • prostaglandins, leukotrienes, and thromboxanes • Cyclic forms • cholesterol, steroid hormones, and bile acids

5. Fatty Acids • Fatty acid: an unbranched-chain carboxylic acid, most commonly of 12 - 20 carbons, derived from hydrolysis of animal fats, vegetable oils, or phospholipids of biological membranes • Usually contain even numbers of carbons (can contain odd, depending on how they are biosynthesized) • FA that contain C=C, are unsaturated: If they contain only C-C bonds, they are saturated • Length of fatty acid plays a role in its chemical character

6. Fig. 8-1a, p. 194

7. Fig. 8-1b, p. 194

8. Fig. 8-1c, p. 194

9. Fig. 8-1d, p. 194

10. Fig. 8-1e, p. 194

11. Fig. 8-1f, p. 194

12. In most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare. Unsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting point.

13. Fatty Acids

14. Fatty Acids

15. In the shorthand notation for fatty acids • saturated FA: the number of carbons then (:) then (0) are shown • unsaturated FA: the number of carbons then (:) then the number and location of double bonds in the chain raised above delta symbol (Δ) are shown, separated by a colon • Note: Counting starts from C of COOH • Examples: palmitic (16:0), stearic (18:0), and oleic acids (18:1Δ9) = double bond between C9 and C10

16. Essential Fatty Acids • They have to be supplied in the diet without exception. • They are all polyunsaturated fatty acids: the C20 fatty acid arachidonic acid (20:4 Δ 5,8,11,14) and the two C18 acids linoleic acid (18:2 Δ 9,12) and linolenic acid (18:3 Δ 9,12 ,15 ). • The animal organism requires arachidonic acid to synthesize eicosanoids.

17. Nutritional fats contain palmitic, stearic, oleic acid, and linoleicacid particularly often. Unsaturated fatty acids are usually found at the central C atom of glycerol.

18. Omega-3 fatty acid • Also called ω-3 fatty acids or n-3 fatty acids are polyunsaturated fatty acids (PUFAs) with a double bond (C=C) at the third carbon atom from the end of the carbon chain. which is considered the beginning of the chain, thus "alpha", and the methyl (-CH3) end, which is considered the "tail" of the chain, thus "omega"; the double bond is at omega minus 3 (not dash 3). One way in which a fatty acid is named is determined by the location of the first double bond, counted from the methyl end, that is, the omega (ω-) or the n- end.

19. The three types of omega-3 fatty acids involved in human physiology are α-linolenic acid (ALA) (found in plant oils), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA)(both commonly found in marine oils). Common sources of plant oils containing the omega-3 ALA fatty acid include walnut, edible seeds, seed oil, algal oil, flaxseed oil, while sources of animal omega-3 EPA and DHA fatty acids include fish, fish oils, eggs from chickens fed EPA and DHA, squid oils. Dietary supplementation with omega-3 fatty acids does not appear to affect the risk of death, cancer or heart disease.

20. Triacylglycerols • Triacylglycerol (triglyceride):an ester of glycerol with three fatty acids • natural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH, in a hydrolysis reaction called saponification (Latin, sapo, soap)

23. Soaps • Soaps form water-insoluble salts when used in water containing Ca(II), Mg(II), and Fe(III) ions (hard water)

24. Hydrolysis of Triglycerides • Chemical hydrolysis, by saponification as mentioned earlier • Enzymatic digestion by lipase enzyme

25. Phosphoacylglycerols • Phosphoacylglycerols (= phospholipids) are the second most abundant group of naturally occurring lipids • found almost exclusively in plant and animal cell membranes, which typically consist of 40% -50% phosphoacylglycerols and 50% - 60% proteins • the most abundant phosphoacylglycerols are derived from phosphatidic acid, a molecule in which glycerol is esterified with two molecules of fatty acid and one of phosphoric acid • the three most abundant fatty acids in phosphatidic acids are palmitic (16:0), stearic (18:0), and linoleic (18:1)

26. Phosphatidic acid

27. Phosphatidic acid

28. Phosphatidic acid

29. Phosphatidyl esters • Further esterification with a low-molecular-weight alcohol with phosphate group gives a phosphoacylglycerol or phosphatidyl ester • the most common of these low-molecular-weight alcohols are:

30. Phosphatidyl esters

31. Phosphatidyl esters

32. Phosphatidyl esters

33. Phosphatidyl esters • A lecithin

34. Pulmonary surfactant Molecular Dynamics simulation of DPPC lipid bilayer formation in two phase systems reduces surface tension

35. Diagram of the alveoli with both cross-section and external view

36. Respiratory Distress Syndrome Result from the Disruption of Lipid Metabolism Respiratory distress syndrome is a pathological condition resulting from a failure in the biosynthetic pathway for dipalmitoyl phosphatidyl choline. This phospholipid, in conjunction with specific proteins and other phospholipids, is found in the extracellular fluid that surrounds the alveoli of the lung, where it decreases the surface tension of the fluid to prevent lung collapse at the end of the expiration phase of breathing. Premature infants may suffer from respiratory distress syndrome because their immature lungs do not synthesize enough dipalmitoyl phosphatidyl choline ( Surfactant ).

37. Waxes A complex mixture of esters of long-chain carboxylic acids and alcohols Found as protective coatings for plants and animals

38. Sphingolipids • Contain sphingosine, a long-chain (18 C) aminoalcohol from which this class is named • Found in plants and animals • Abundant in nervous system choline

39. Glycolipids • Glycolipid: a compound in which a carbohydrate is bound to an -OH of the lipid • many glycolipids are derived from ceramides • Ceramide + simple sugar= cereboside (found in nerves and brain cells)

40. Fig. 8-8, p.190

41. Tay-Sachs disease It is caused by a failure of lipid degradation: an inability to degrade gangliosides. Gangliosides are found in highest concentration in the nervous system, particularly in gray matter, where they constitute 6 % of the lipids. Gangliosides are normally degraded inside lysosomes by the sequential removal of their terminal sugars but, in Tay-Sachs disease, this degradation does not occur. As a consequence, neurons become enormously swollen with lipid-filled lysosomes . An affected infant displays weakness and retarded psychomotor skills before 1 year of age. The child is demented and blind by age 2 and usually dead before age 3.

42. Tay-Sachs disease can be diagnosed in the course of fetal development. Amniotic fluid is obtained by amniocentesis and assayed for β-N-acetylhexosaminidase activity.

43. Multiple sclerosis (MS) It is a demyelinating disease in which the insulating covers of nerve cells in the brain and spinal cord are damaged.This damage disrupts the ability of parts of the nervous system to communicate, resulting in a range of signs and symptoms, including physical, mental, and sometimes psychiatric problems.

44. END