BCH 3000 PRINCIPLES OF BIOCHEMISTRY

Transcription

1 BCH 3000 PRINCIPLES OF BIOCHEMISTRY (Semester /13) 1

2 LIPID Learning outcome (Objectives) Function and distribution. Characteristics of fatty acids-structure and chemical properties. Saturated and unsaturated fatty acids. Structures and properties of phospholipids, sphingolipids, waxes, terpenes and steroids. 2

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7 LIPID DEFINITION : General definition all compounds called fat and oils TECHNICAL DEFINITION Fat : Triglycerides in the form of solids at room temperature Oils : Triglycerides which are liquid at room temperature 7

8 General Definition Any natural compound which is insoluble or nearly insoluble in water but soluble in nonpolar solvents a. Chloroform b. CS 2 c. Ether d. warm or e. hot ethanol 8

9 FUNCTIONS Lipids are widely distributed in both animal and plant systems and perform a wide variety of functions i. Structural functions - Components of membranes ii. iii. iv. Storage forms of carbon and energy precursor for major compounds e.g. hormones. Insulators - thermal, electrical or physical shock v. protective coatings prevent infections, loss or addition of compounds vi. Regulators - as vitamins & hormones 9

10 CLASSIFICATION 1. SIMPLE LIPIDS Fatty acid esters (Acid + alcohol ester) 2. COMPPOUND LIPID Fatty acid + alcohol + OTHER COMPOUNDS 10

11 LIPID COMPONENTS Acyglycerols (Glycerol + Fatty acids) = Waxes Alcohol + fatty acids SIMPLE LIPIDS??? Esters 11

12 COMPOUND LIPIDS 4 types of Compound lipid i. Phosphoglycerides ii. iii. iv. Sphingolipids Cerebrosides Gangliosides 12

13 i LIPID Phosphoglycerides COMPONENTS Glycerol + Fatty acid +HPO satu OHR ii iii iv Sphingolipids Cerebrosides Gangliosides Sphingosine + Fatty acid + HPO Choline Sphingosine +Fatty acid + Simple sugar Sphingosine + Fatty acid+ 2-6 Simple sugar (Including sialic acid) COMPOUND LIPID 13

14 i & ii = Phospholipid - presence of phosphate ii, iii & iv = Sphingolipids - presence of Sphingosine iii & iv = glycolipid - presence of carbohydrate 14

15 GLYCEROL Trihydroxy alcohol 15

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17 FATTY ACIDS Long chain aliphatic carboxylic acids- contains carboxyl group polar head and `tail containing hydrocarbon chain Amphiphilic compounds hydrophilic head and hydrophobic tail COOH can be ionised Monocarboxyilic acids linear hydrocarbon chain, even carbon numbers between C 12 -C 20 Short, longer, branched, cyclic and odd numbers also exist BUT not many 17

18 Octadenic acid 18

19 FATTY ACIDS 2 TYPES 1. Saturated Fatty acids 2. Unsaturated Fatty acids 19

20 Structure of Fatty Acids - Saturated Fats mostly from animal sources, have all single bonds between the carbons in their fatty acid tails, thus all the carbons are also bonded to the maximum number of hydrogens possible. saturated fats The hydrocarbon chains in these fatty acids are, thus, fairly straight and can pack closely together, making these fats solid at room temperature. 20

21 Saturated fatty acid e.g. 1. palmitic acid (CH 3 (CH 2 ) 14 COOH) (16C) & 2. Stearic acid (CH 3 (CH 2 ) 16 COOH) 21

22 Saturated Fatty Acids 22

23 Structure of Fatty Acids - Unsaturated Unsaturation normally at - C 18 & C 20 double bond separated by methylene group -CH = CH - CH 2 - CH = CH Double bonds = cis configuration Unsaturated fatty acid - oleic (18:1), Linoleic (18:2), Linolenic (18:3) & arachidonic (18:4) 23

24 Unsaturated fatty acids C=C double bond arranged in two ways In cis bonds, the two pieces of the carbon chain on either side of the double bond are either both up or both down, such that both are on the same side of the molecule In trans bonds, the two pieces of the molecule are on opposite sides of the double bond, that is, one up and one down across from each other Naturally-occurring unsaturated vegetable oils have almost all cis bonds, but using oil for frying causes some of the cis bonds to convert to trans bonds 24

25 TRANS CIS 25

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27 Unsaturated Fatty Acids 27

28 fatty acids with trans bonds are carcinogenic, or cancer-causing. containing products such as margarine are quite high, 28

29 Oils mostly from plant sources, have some double bonds between some of the carbons in the hydrocarbon tail, causing bends or kinks in the shape of the molecules. Because some of the carbons share double bonds, they re not bonded to as many hydrogens oils are called unsaturated fats. kinks unsaturated fats can t pack as closely together, making them liquid at room temperature 29

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32 Making margarine Vegetable oils often contain high proportions of polyunsaturated and mono-unsaturated fats (oils) liquids at room temperature. You can "harden" (raise the melting point of) the oil by hydrogenating it in the presence of a nickel catalyst. 32

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35 SIMPLE LIPIDS 2 GROUPS i. Neutral acyglycerols (e.g. Triacylglycerol) ii. Waxes Acyglycerols = glyceride = a tryhydroxy alcohol ester = glycerol + fatty acid (3 different fatty acids) = can be esterified 35

36 Glycerol = trihydroxy alcohol 36

37 TRIACYGLYCEROLS 37

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42 Triacylglycerol the most abundant No ionic groups - neutral lipids Triacylglycerol = neutral fats neutral oils (liquid) 42

43 FUNCTIONS IN ANIMALS I. Adipose tissues - `fat depots' = storage forms of carbon and energy II. III. Transport - chylomicrons - = lipoprotein fatty acids are transported through lymphatic system and blood tissue adipose tissues and other organs `Physical protection' - e.g. temperature. 43

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47 WAXES Also an ester - alcohol & fatty acid = very long hydrocarbon chain commercial application hairs, skin, leaves, fruits 47

48 WAXES Asid Oleic 48

49 CHEMICAL CHARACTERISTICS OF TRYACYLGLYCEROL (Reactions of Triacylglycerol) 1. Hydrogenation 49

50 Double bonds in vegetable oils can be hydrogenated oils become solids can control - e.g.. peanut butter - crunchy, creamy HYDROGENATION PROCESS 50

51 2. Halogenation Addition of halogens Other halides - Iodine(I 2 ), Chlorides (Cl 2 ) 51

52 Saturated fatty acid iodine number = 0 Oleic acid - 90, linoleic- 181, Linolenic =

53 Animal fat-iodine number is low Vegetable oils iodine number is high 53

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55 3. Hydrolysis (i.) Base Hydrolysis Fatty acid + Glycerol or Salts of fatty acid + Glycerol inside cells by enzymes (lipase) very specific for ester bonds products are glycerol + fatty acids Non-enzymatic- with alkali (base) salts of fatty acid + Glycerol salts of fatty acids = soap Base Hydrolysis = SAPONIFICATION 55

56 SAPONIFICATION The reaction of triacylglycerol with base (alkali) - e.g.. NaOH, KOH Triacylglycerol presence of strong ester bond Ester bond can be hydrolyzed by base salts of fatty acid + glycerol Salts = soap react as a soap/detergent 56

57 Saponification reaction (Base Hydrolysis) 57

58 If R= palmitic acid Sodium palmitate If R = oleic acid Sodium oleate R = stearic acid Sodium stearate 58

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60 Detergent? =`surface active agents' lower surface tension of surface of water H 2 O = `poor cleansing agent - Y? Because the molecule is very polar and tend to stick to each other therefore cannot enter non-polar areas like grease, oil, dirt 60

61 HOW DOES A DETERGENT WORK?? i. Hydrophobic tails enters grease layers ii. Hydrophilic heads come into contact with aqueous layer separate grease layer from the surface iii. Small grease globules form- `pincushion iv. These globules have similar charges - therefore cannot go near each other can wash 61

62 Water Grease 62

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65 Head - Polar (hidrofilik) Ekor- Tak polar (Hidrofobik) 66

66 (ii). Acid Hydrolysis Carboxylic acids 67

67 Expose triacylglycerol to warm and moist air rancid (tengik) 2 reactions take place 1. Ester hydrolysis 4. RANCIDITY 2. Oxidation of the double bonds Hydrolysis - water (inside the lipid) + enzyme (bacteria in the air) Oxidation-by O 2 on the side chain of triacylglycerol short chain fatty acids rancid (tengik) 68

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69 Phosphoglycerides Phosphoglycerides = Phosphoglycerol i.e. they are derived from glycerol Fatty acids Glycerol Phosphate group 70

70 other alcohols Phosphoglycerol = Phosphoglyceride 71

71 Glycerol (Trihydroxyglycerol) Phosphatidic acid (Glycerol + 2 fatty acids + Phosphate) Phosphoglyceride (Phosphoglycerol) (Glycerol + 2 fatty acids + Phosphate + other group e.g.. alcohol) 72

72 All phosphoglycerides are Phospholipids!!!! 73

73 Phosphoglycerides can be further esterified to form other lipids i. Phosphatidylcholine ( choline ester) ii. iii. Phosphatidylethanolamine (ethanolamine) Phosphatidylserine (serine) All are important components of membranes 74

74 Asid lemak Phosphate 75

75 Phosphatidylethanolamine 76

76 Phosphatidylethanolamine 77

77 Phosphatidylserine 78

78 Membrane 79

79 SPHINGOLIPID No glycerol replaced with amine alcohol = Sphingosine Number of carbon atoms varies The simplest = ceramides = Fatty acid + sphingosine through amino group via amide bond Sphingomyelin an example of sphingolipid - 1 o alcohol esterified to phosphate amino alcohol (= choline) Found in nerve membranes and brain 80

80 SPHINGOLIPID 1. What is the main structure for sphingolipid? Sphingosine 2. Draw the structure of sphingosine 3. Draw the structure of glycerol and compare between the two CH CH(CH 2 ) 12 CH 3 CHOH Sphingosine CH NH 2 CH 2 OH H 2 C OH H 2 C OH H 2 C OH Glycerol 81

81 SPHINGOLIPID No glycerol replaced with amine alcohol = Sphingosine Number of carbon atoms varies The simplest = ceramides = Fatty acid + sphingosine through amino group via amide bond Sphingomyelin an example of sphingolipid - 1 o alcohol esterified to phosphate amino alcohol (= choline) Found in nerve membranes and brain 82

82 CERAMIDE 83

83 Phosphate Choline 84

84 GLYCOLIPID When a carbohydrate is attached to OH- via glycosidic bond Seb. induk = ceramide (sphingolipid) + CHO Cerebroside - CHO = galactose glucocerebroside GANGLIOSIDE ALSO contains oligosaccharide + sialic acid 85

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86 DERIVED LIPIDS A heterogeneous group Derived from fatty acids steroids, prostaglandin, leukotriene, carotenoids, vitamin STEROID All organisms similar basic structure fused ring= perhydrocylopentanophenanthrene 87

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89 STEROL i. Hydrocarbon chain (C18-C20) at C17 ii. Hydroxyl group (OH) at C3 Main example = CHOLESTEROL structural component of membrane % lipid membrane. Rigid Precursor of bile, sex hormones, vit. D. Role in atherosclerosis 90

90 Hydrocarbon chain at C17 OH at C3 CHOLESTEROL 91

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92 TERPENE Lipid derived from isoprene Term used for all compounds synthesized from the precursor isoprene cholesterol, bile acid, steroid, lipid soluble vitamins = terpene Oils from turpentine (pine tree extracts) formula C 10 H 15 > 15 carbon atom also found - `multiples of 5 Also in other plants 93

93 TERPENE Terpene with 20 carbon atoms - vit. A - 40 carbon atoms - b- carotene EXAMPLES: 1. monoterpene - Limonene - `odor' lemon 2. Diterpene - Gibberrelic acid plant hormone 3. Triterpene - Squalene Cholesterol precursor 4. Tetraterpene - Lycopene - tomato pigments 94

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97 BCM 3000 PRINCIPLES OF BIOCHEMISTRY (Semester /12) 98

98 LIPID BEHAVIOUR IN WATER Lipid not soluble in water but can still be found in aqueous environment behavior in water important to understand the phenomena A lot of lipids are amphiphyllic = having hydrophobic part (hydrocarbon chain) polar (ionic) part 99

99 When lipid is dispersed in water, the hydrophobic part will segregate from the solvent through `self-aggregation' form a. micelles which are dispersed in water b. monolayers ( aggregate boundary H 2 O: air 100

100 MICELLES MONOLAYER 101

101 The tendency for hydrocarbon chains to distance away from polar solvents gives rise to = HYDROPHOBIC EFFECT Most lipids will form micelles spheres, ellipse, discs, cylinders Also can form vesicles bilayer hydrocarbon chains are opposite to each other `hollow sphere' 102

102 Micelle Vesicles Bilayer 103

103 BILAYER 104

104 Cholesterol does not form micelles?? Not amphiphatic compounds Structure flat fused ring - solid difficult to form micelles Can form mixed micelle with amphiphatic lipids mixed micelles with amphiphatic lipids 105

105 BILE ACID AND BILE SALTS Bile acids serve many functions. They aid in fat absorption Bile acids are produced from cholesterol in the liver. Cholesterol is converted to the carboxylic acids cholic and chenodeoxycholic acid, which are the primary bile acids in most species. The liver conjugates the acids to either glycine or taurine and subsequently secrets them into the bile. The gall bladder serves to store bile acids until contraction associated with feeding 106

106 Glycine Taurine 107

107 LIPOPROTEIN Particles that contain lipid and protein bonds = not (non-covalent) bonds Function In blood plasma to transport triacylglycerol and cholesterol STRUCTURE - form `micelle like particles' - i. core non-polar triacylglycerol ii. Surrounded by a layer of amphiphilic protein, phospholipid and cholesterol 108

108 Various categories depending on the functions i. CHYLOMICRON Carries exogenous triacylglycerols & cholesterol (from diet) from intestine to the tissues. ii. LDL, IDL & LDL group of related particles which carry endogenous triacylglycerols & cholesterol (produced internally) from the liver to tissues NB: liver can synthesize triacylglycerol from excess carbohydrate 109

109 CHYLOMICRON 110

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111 LDL, CHOLESTEROL & ATHEROSCLEROSIS Cholesterol Important component of membrane can be supplied from the outside or internally (if not enough) How obtained externally? ENDOCYTOSIS Through reaction of specific receptors = LDL receptor? protein part of LDL tie up to R-LDL in the cell complex `pinched off' = endocytosis 112

112 ENDOCYTOSIS vs EXOCYTOSIS 113

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114 Protein recycled used in the cell Oversupply? Synthesis of R-LDL inhibited low LDL cholesterol level in blood increases deposited in the artery heart disease; stroke HDL Function opposite of LDL Carries cholesterol from tissues - extract cholesterol from membrane change to `cholesteryl esters - LCAT (Lecithin cholesterol transferase) bile acids 115