Chapter 19. Lipids

1. Chapter 19. Lipids Sections

2. Chapter 19 19.1 Structure and Classification of Lipids19.2 Fatty Acids: Lipid Building Blocks19.3 Physical Properties of Fatty Acids19.4 Energy-Storage Lipids: Triacylglycerols19.5 Dietary Considerations and Triacylglycerols19.6 Chemical Reactions of Triacylglycerols19.7 Membrane Lipids: Phospholipids19.8 Membrane Lipids: Sphingoglycolipids19.9 Membrane Lipids: Cholesterol19.10 Cell Membranes19.11 Emulsification Lipids: Bile Acids19.12 Messenger Lipids: Steroid Hormones19.13 Messenger Lipids: Eicosanoids19.14 Protective-Coating Lipids: Biological WaxesChemistry at a Glance: Types of Lipids and How They FunctionChemical Connections: The Fat Content of Tree Nuts and Peanuts; Artificial Fat Substitutes; The Cleansing Action of Soap; Trans Fatty Acids and Blood Cholesterol Levels; Steroid Drugs in Sports; The Mode of Action for Anti-Inflammatory Drugs

3. Lipids A heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties • insoluble in water • soluble in aprotic organic solvents including diethyl ether, dichloromethane, and acetone Lipids include • Waxes • triglycerides • phospholipids • Prostaglandins • cholesterol, steroid hormones, and bile acids • fat-soluble vitamins

4. Structure and Classification of Lipids Lipids that are ester or amides of fatty acids: Waxes – are carboxylic acid esters where both are carboxylic acid esters where both R groups are long straight hydrocarbon chain. R groups are long straight hydrocarbon chain. Performs external protective functions. Performs external protective functions. Triglycerides– are carboxylic acid are carboxylic acid triesters of Glycerols . They are a major source of biochemical energy. Glycolipids– amides derived from sphingosine, contain polar carbohydrate groups. On the cell surface, they connect with intracellular messengers. Glycerophopholipids –triesters of glycerols that contain charged phosphate diesters. They help to control the flow of molecules into and out of cells. Sphingomyelins– amides derived from an amino alcohol, also contain charged amino alcohol, Phosphate diester groups. They are essential to the structure of cell membranes. Lipids that are not esters or amides: Steroids – They performs various functions They performs various functions such as hormones and contributes to the structure of cell membranes. Eicosanoids– They are carboxylic acids that are a special type of intracellular chemical messengers.

5. Wax esters are fatty acids esterified to long-chain saturated or monoenoic (one double bond) alcohols. They are carboxylic acid esters where both are carboxylic acid esters where both R groups are long straight hydrocarbon chain. R groups are long straight hydrocarbon chain. They performs external protective functions. Performs external protective functions. Beeswax Spermaciti: sperm whale wax

6. Spermaceti source Carnauba wax source Bee’s wax

7. Triglycerides

8. Properties of Fats and Oils Oils: A mixture of triglycerides that is liquid because it contains a high proportions of unsaturated fatty acids. Fats : A mixture of triglycerides that is solid because it contains a high proportions of saturated fatty acids.

9. Physical properties of Triglycerides Depends on their fatty acid components • melting point increases as the number of carbons in their hydrocarbon chains increases and as the number of double bonds decreases • triglycerides rich in unsaturated fatty acids are generally liquid at room temperature and are called oils • triglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature and are called fats

10. Triglycerides The lower melting points of triglycerides rich in unsaturated fatty acids are related to differences in their three-dimensional shape • hydrocarbon chains of saturated fatty acids can lie parallel with strong dispersion forces between their chains; they pack into well-ordered, compact crystalline forms and melt above room temperature • because of the cis configuration of the double bonds in unsaturated fatty acids, their hydrocarbon chains have a less ordered structure and dispersion forces between them are weaker; these triglycerides have melting points below room temperature

11. Reduction of Triglycerides • the process of converting fats to oils is called hardeningand involves catalytic reduction of some or all of an oil’s carbon-carbon double bonds • in practice, the process is controlled to produce a fat of a desired consistency • the resulting fats are sold for cooking (Crisco, Spry, and others) • margarine and other butter substitutes are produced by partial hydrogenation of polyunsaturated oils derived from corn, peanuts, and soybeans • because catalytic hydrogenation is to some degree reversible, hardening results in the isomerization of some cis-fatty acids to trans-fatty acids; trans fatty acids are to be avoided as much as possible

12. Triglycerides An ester of glycerol with three fatty acids

13. Soaps and Detergents Natural soaps are prepared by boiling lard or other animal fat with NaOH, in a reaction called saponification (Latin, sapo, soap)

14. Soaps and Detergents Soaps clean by acting as emulsifying agents • the long hydrophobic hydrocarbon chains of soaps are insoluble in water and tend to cluster in such a way as to minimize their contact with water • the polar hydrophilic carboxylate groups tend to remain in contact with the surrounding water molecules • driven by these two forces, soap molecules spontaneously cluster into micelles • Micelle: a spherical arrangement of organic molecules in water clustered so that their hydrophobic parts are buried inside the sphere and their hydrophilic parts are on the surface of the sphere and in contact with water

15. Soaps and Detergents • when soap is mixed with water-insoluble grease, oil, and fat stains, the nonpolar parts of the soap micelles “dissolve” nonpolar dirt molecules and they are carried away in the polar wash water

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

17. Synthetic Detergents The design criteria for a good detergent are • a long hydrocarbon tail of 12 to 20 carbons • a polar head group that does not form insoluble salts with Ca(II), Mg(II), or Fe(III) ions • the most widely used synthetic detergents are the linear alkylbenzenesulfonates (LAS) • also added to detergent preparations are foam stabilizers, bleaches, and optical brighteners

18. Fatty Acids A long, unbranched chain carboxylic acid • nearly all have an even number of carbon atoms, most between 12 and 20, in an unbranched chain • the three most abundant are palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1) • 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

19. Fatty Acids The most abundant fatty acids

20. Saturated Fatty Acids

22. Unsaturated Fatty Aicds

23. Saturated/unsturated fatty acids

24. Saturated/unstaureated Mixtures

25. Fatty Acids the greater the degree of unsaturation the lower the melting point

27. What are "Omega" series fatty acids? Scientists differentiate fatty acids by the characteristics of their molecules. The two principal essential fatty acids are Omega-6 (n-6) series and the Omega-3(n-3) series. The number indicates the position of the first double carbon bond when counting from a specified end of the molecule.

28. Essential Fatty Acids Fatty acids that cannot be produced by the body and are necessary for proper metabolism. The OMEGA 6 and OMEGA 3 fatty acids are referred to as Essential Fatty Acids (EFA).

29. Phospholipids Phospholipids are the second most abundant group of naturally occurring lipids • they are found almost exclusively in plant and animal membranes, which typically consist of 40% to 50% phospholipids and 50% to 60% proteins • the most abundant phospholipids are derived from phosphatidic acid, a molecule in which glycerol is esterified with two fatty acids and one phosphoric acid • further esterification with a low-molecular weight alcohol gives a phospholipid • the three most abundant fatty acids in phosphatidic acids are palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1)

30. Phospholipids Phosphate(PO4 )-containing molecules with structures related to the triglycerides are aclledGlycerophopholipids E.g. Phosphatidycholine (lecithin)

31. Examples of glycerophospholipids

32. Phospholipids A phosphatidate and a phospholipid

33. Phospholipids

34. Phosphatidycholine (lecithin)

35. Phospholipids • low-molecular weight alcohols in phospholipids

36. Lipid Bilayer When placed in aqueous solution, phospholipids spontaneously form a lipid bilayer • polar head groups lie on the surface, giving the bilayer an ionic coating • nonpolar fatty acid hydrocarbon chains lie buried within the bilayer This self-assembly is driven by two noncovalent forces • hydrophobic effects, which result when nonpolar hydrocarbon chains cluster to exclude water molecules • electrostatic interactions, which result when polar head groups interact with water and other polar molecules in the aqueous environment

37. Plasma membrane Planar lipid bilayers Biological membranes are bilipid layers . In a real cell the membrane phospholipids create a spherical three dimensional lipid bilayer shell around the cell. However, they are often represented two-dimensionally as: Passive tranport Active transport

38. Biological Membranes Fluid mosaic model: a biological membrane consists of a phospholipidbilayer with proteins, carbohydrates, and other lipids embedded on the surface and in the bilayer • fluid signifies that the protein components of membranes “float” in the bilayer and can move freely along the plane of the membrane • mosaic signifies that the various components of the membrane exist side by side, as discrete units rather than combining to form new molecules and ions

39. Fluid-Mosaic Model

40. Prostaglandins Essential fatty acids in the cell membranes produce prostaglandins. Prostaglandins regulate bodily functions in the heart, kidneys, liver, lungs, brain, nerves and the immune system.

41. Types of Prostaglandins In human beings, there are three families of prostaglandins, each of which is derived from a different fatty acid. Prostaglandin PG PGE1 PGF1 PGE2 PGF2 Eicosanoids Thromboxane A2 LeukotrieneB4

42. Prostaglandins Prostaglandins: a family of compounds that have the 20-carbon skeleton of prostanoic acid

43. Prostaglandins Prostaglandins are not stored in tissues as such, but are synthesized from membrane-bound 20-carbon polyunsaturated fatty acids in response to specific physiological triggers • one such polyunsaturated fatty acid is arachidonic acid

44. Prostaglandins • among the prostaglandins synthesized biochemically from arachidonic acid are

45. Prostaglandins • the observation that PGF2a stimulates contractions of uterine smooth muscle led to the development of synthetic PGFs that can be used for therapeutic abortions

46. Prostaglandins • the PGE1 analog, misoprostol, is used to prevent the ulceration associated with the use of aspirin-like NSAIDs

47. Eicosanoids The prostaglandins are members of an even larger family of compounds called eicosanoids, all of which contain 20 carbons and are derived from polyunsaturated fatty acids • thromboxanes

48. Eicosanoids Leukotrienes • found primarily in white blood cells • one function is constriction of smooth muscles, especially those of the lungs

49. Eicosanoids Prostacyclin

50. Steroids A group of plant and animal lipids that have this tetracyclic ring structure