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Chapter 3. Lipids

Chapter 3. Lipids. Biological lipids are a chemically diverse group of compounds, which are highly soluble in nonpolar solvents but not in water. They are either hydrophobic or amphipathic. Introduction Storage lipids Structural lipids Active lipids Glycolipids and lipoproteins

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Chapter 3. Lipids

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  1. Chapter 3. Lipids Biological lipids are a chemically diverse group of compounds, which are highly soluble in nonpolar solvents but not in water. They are either hydrophobic or amphipathic. • Introduction • Storage lipids • Structural lipids • Active lipids • Glycolipids and lipoproteins • Separation and analysis of lipids

  2. P.79 I. Introduction

  3. Membrane structure

  4. Amphipathic lipid aggregates that form in water 两亲性 Vesicle Emulsion Emulsification Critical micelle concentration (CMC) Sodium dodecyl sulfate (SDS)

  5. P.80 Biological Functions Fatty acids (脂肪酸) Triacylglycerols (三酰甘油) Wax (蜡) Storage lipids (贮存脂质) Phospholipids (磷脂) Glycolipids (糖脂) Sterols (甾醇) Structural lipids (结构脂质) Lipids I. Introduction Terpenes (萜) Steroids (类固醇) Lipoproteins (脂蛋白) Active lipids (活性脂质)

  6. II. Storage Lipids • Fatty acids (脂肪酸) • Triacylglycerols (三酰甘油) • Wax (蜡)

  7. 1. Fatty acids II. Storage lipids Compositions & classifications (组成和分类) Saturated and unsaturated fatty acids (饱和与不饱和脂肪酸) Nomencluture (命名) Fatty acids in food Essential fatty acids (必需脂肪酸) Physical properties Chemical properties

  8. (1). Compositions & classifications(组成和分类) Saturated (饱和脂肪酸) Monounsaturated (单不饱和脂肪酸) ‘Tail’ – hydrophobic chain (C4-C36) 疏水长链 Unsaturated (不饱和脂肪酸) Fatty acid 亲水基团 Polyunsaturated (多不饱和脂肪酸) ‘Head’ – hydrophilic group (-COO-) • Most common: • Even No. of C (偶数C) • Unbranched (无支链) • C12-C24

  9. (2). Saturated and unsaturated fatty acids Saturated fatty acids (饱和脂肪酸): • Flexible structure, with the fully extended conformation the most stable (结构灵活) • Close packing (紧密堆积) • High melting point (高熔点, e.g. beef oil) Unsaturated fatty acids (不饱和脂肪酸) : • Slightly more abundant in nature • ‘Kinks’ in the chain – resulting in flexible, fluid aggregates • The most common one is oleic acie (油酸): 18:1 9c • C=C bond usually in cis-form, rarely in trans-form • Common location of C=C bonds: • Monounsaturated:C9=C10 • Polyunsaturated:C9=C10, C12=C13, C15=C16, II. Storage lipids

  10. (3). Nomencluture (命名) 18:29c,12c Chain length (链长,总C数) cis-trans configuration of C=C (双键的顺反构型) No. of C=C bonds (双键数) Position of C=C bonds (双键的位置)

  11. (4). Fatty acids in food • Vegetable oils vs. animal oils and fats • Unsaturated fatty acids vs. saturated fatty acids • Unsaturated fatty acids: cis vs. trans • Trans fat and hydrogenated vegetable oil Example 1. Olive oil – rich in oleic acid (monounsaturated) Example 2. Margarine – a substitute for butter II. Storage lipids

  12. Partial hydrogenation of cooking oils • shelf lives  (∵m.p.) •  trans fatty acids  Higer incidence of cardiovascular disease

  13. 棕榈酸 (5). Essential fatty acids (EFA, 必需脂肪酸) 棕榈油酸 硬脂酸 油酸 亚油酸 Eicosapentaenoic acid (EPA) 20:5(5,8,11,14,17) 十二碳五烯酸 Docosahexaenoic acid (DHA) 22:6(4,7,10,13,16,19) 二十二碳六烯酸 ALA,亚麻酸 — those that are not synthesized by mammals and yet are necessary for normal growth and life. 花生四烯酸

  14. Omega-3 (-3) fatty acids -6 PUFAs = 1:1 ~ 4:1 -3 PUFAs 亚麻酸，18:3(9,12,15): -linolenic acid (ALA), an -3 fatty acid -linolenic acid (GLA), an -6 fatty acid Polyunsaturated fatty acids (PUFAs) with a double bond between C3 and C4 from the methyl end of the chain. Specially important in human nutrition Optimal dietary ratio:

  15. Humans can synthesize EPA and DHA from ALA Essential fatty acid -linolenic acid (ALA) 18:3(9,12,15) 亚麻酸 Eicosapentaenoic acid (EPA) 20:5(5,8,11,14,17) 十二碳五烯酸 Docosahexaenoic acid (DHA) 22:6(4,7,10,13,16,19) 二十二碳六烯酸 All the 3 are -3 fatty acids, all important in cellular function.

  16. (6) Physical properties (物理性质) Modified, e.g. esterified (如：脂肪酸酯化) Carboxylic head (羧基头) Solubility  (溶解度) Chain length  (烃链长度) Hydrocarbon tail (烃链) Melting point  (熔点) Unsaturation degree  (烃链的不饱和程度)

  17. P.86 (7). Chemical properties • Oxidation (氧化) and peroxidation (过氧化) • Addition (加成) • Hydrogenation (氢化) • Halogenation (卤化) • Emulfication (乳化): Amphipathy (两亲性) Emulsifier (乳化剂) Detergent (去污剂) Surfactant (表面活性剂) II. Storage lipids 十二烷基硫酸钠 (Sodium dodecyl sulfate, SDS) Ionic detergent

  18. P.91 2. Triacylglycerols (三酰甘油) 1). Triacylglycerol (三酰甘油) = Triglyceride (甘油三脂), TG -- Triester of glycerol with 3 fatty acids (甘油和脂肪酸形成的三酯) 2). The central C is a prochiral center -- sn-system 3). Classification: Simple triacylglycerol (简单三酰甘油) Triolein (三油酸甘油脂) Tristearin (三硬脂酸甘油脂) Mixed triacylglycerol (混合三酰甘油) 1-棕榈酰-2-硬脂酰-3-豆蔻酰-sn-甘油 Monoacylglycerol (单酰甘油) Diacylglycerol (二酰甘油) Triacylglycerol (三酰甘油) 简单三酰甘油: R1 = R2 = R3 混合三酰甘油: R1, R2, R3不完全相同

  19. Nomencluture of glycerol derivatives: sn-system(Stereospecific numbering system)  sn-甘油-3-磷酸 L-configuration

  20. General structrure of a triacylglycerol Hydrolysis by: H+ OH- Lipases (脂肪酶) Oil (油) – liquid Fat (脂) – solid

  21. P.93 2. Triacylglycerols (continued) 4) Physical properties (物理性质): a. Color and odor (颜色和气味) Colorless, odorless, tasteless b. Density and solubility (密度和溶解度) Density < 1 g/cm3 Insoluble in H2O, soluble in nonpolar solvents TGs are nonpolar, hydrophobic molecules: c. Melting point (熔点) Chain length, m.p. Double bonds, m.p. Olive oil – liquid Beef fat – solid II. Storage lipids

  22. P.94 2. Triacylglycerols (continued) 5) Chemical properties (化学性质): a. Hydrolysis (水解) and saponification (皂化) -- Saponification value (皂化值) -- Used for estimation of the molecular weight (用于估计分子量). b. Hydrogenation (氢化) and halogenation (卤化) -- Iodine value (碘值) -- Used for estimation of the unsaturation degree (用于估计不饱和度). c. Acetylation (乙酰化) -- Acetylation number (乙酰值) -- Used for estimation of the number of free –OH (用于估计自由羟基数) d. Rancidity (酸败) and autoxidation (自动氧化) -- Acid value (酸值) --Used for estimation of the rancidity degree (用于估计酸败程度) II. Storage lipids

  23. Saponification value (皂化值) • Saponification value is the mg of KOH required to saponify 1g of a TG (皂化值是皂化1g三酰甘油所需要的KOH的mg数). • It can be used to estimate the molecular weight of a TG (皂化值可帮助估计三酰甘油的分子量). x y 皂化值 x/1000 1 : = 1: 3 y KOH 分子量

  24. Iodine value (碘值) x • The iodine value represents how many grams of I2 are required for the halogenation reaction of 100 g of a TG (碘值指100g油脂卤化时所能吸收碘的克数) • It can be used to estimate the unsaturation level of the TG (碘值可用于估计油脂的不饱和度) Suppose the TG contains y double bonds, y 碘值 100 x : = 1 : y MW I2 TG不饱和键数 TG分子量

  25. Acetylation number (乙酰值) x • It is the mg of KOH required to neutralize the CH3COOH released from 1 g of an acetylated product (乙酰值指从1g油脂乙酰化产物中释放的乙酸所需的KOH的mg数). • It is used to represent how many hydroxyl groups are available in the TG (用于表示油脂的羟基化程度). y Hydrolysis Acetylation KOH CH3COOR CH3COOH : R-OH 水解 乙酰化 乙酰值 1 x/1000 = 1: y : MW KOH TG分子量 TG的自由羟基数

  26. Acid value (酸值) • It is the mg of KOH required to neutralize the free fatty acids released from 1 g of a TG (酸值是中和1 g油脂中的游离脂肪酸所需的KOH的mg数) • It is used to estimate the rancidity degree of the TG (用于估计油脂的酸败程度) • Two major reasons for rancidification (酸败): • Autoxidation (自氧化) • Microbial effects (微生物效应)

  27. 2. Triacylglycerols (continued) 6) Major use of TGs in animals and plants • Energy storage • Insulation • Examples: Polar bears & Sperm whales II. Storage lipids The mighty whales swim in a sea of water, and have a sea of oil swimming in them.

  28. Glucose and glycogen can work as quick sources of metabolic energy (∵ready solubility in water) Triglycerols vs. starch/glycogen 2 advantages of using triglycerols as stored fuels Fats – to meet energy needs for months Glycogen – less than a day’s energy supply The human body can store • More reduced  more energy to be released when oxidized • More hydrophobic  no need to carry extra water for hydration

  29. P.95 3. Wax • Esters of long-chain fatty acids with long-chain alcohols • Energy stores and water repellents • Applications Weakly polar head group C14-C36 C16-C36 II. Storage lipids Nonpolar tails Triacontanoylpalmitate, the major component of beeswax

  30. A honeycomb constructed of beeswax

  31. III. Structural Lipids Glycerophospholipids (甘油磷脂) Glycolipids (糖脂) Archaeal ether lipids (古细菌醚脂) Sphingolipids (鞘脂类) Sterols (甾醇)

  32. Principal classes of storage and membrane lipids 膜脂 鞘氨醇 古细菌醚脂 糖脂 磷脂 三酰甘油 甘油磷脂 phosphosphingolipids 鞘磷脂 （鞘氨醇磷脂） glycosphingolipids 鞘糖脂 Sterols (甾醇) Sphingolipids (鞘脂类)

  33. P.103 1. Glycerophospholipids (甘油磷脂) Glycerophospholipids (甘油磷脂) ‖ Phosphoglycerides (磷酸甘油脂) III. Structural Lipids C-1: C16 or C18, saturated fatty acid D-Glycerol 3-phosphate, the backbone of phospholipids Nonpolar tail (非极性尾部) C-2: C18 or C20, unsaturated fatty acid Polar head (极性头)

  34. 两亲性 手性 电荷 磷脂酸 磷脂酰乙氨醇 (脑磷脂) cephalin 磷脂酰胆碱 (卵磷脂) lecithin The charge on the polar head contributes greatly to the surface properties of membranes

  35. 2. Glycolipids (糖脂) • Galactolipids (半乳糖脂) and sulfolipids (硫脂) are predominate in plant cells. • Galactolipids are localized in the thylakoid (类囊体) membranes of chloroplasts, making up 70-80% of the total membrane lipids of a vascular plant. • Galactolipids are probably the most abundant membrane lipids in the biosphere. 3 glycolipids of chloroplast thylakoid membranes

  36. 3. Archaeal ether lipids (古细菌醚脂) • Archaea contain unique membrane lipids – ether lipids. • The general name for these lipids: glycerol dialkyl glycerol tetraethers (GDGTs) • These ether linkages are much more stable to hydrolysis at low pH and high temperature. • Archaea live in ecological niches with extreme conditions: e.g., high temperature, low pH, high ionic strength. Long chain (32 carbons) branched hydrocarbons A typical membrane lipid of archaea

  37. 4. Sphingolipids (鞘脂类) 两亲性 手性 电荷 Sphingosine (鞘氨醇) as the backbone Fatty acid chain III. Structural Lipids 神经酰胺 (ceramide)：X = H 鞘磷脂 (phosphosphingolipid): X = 磷酰胆碱，磷酰乙醇胺 鞘糖脂 (glycosphingolipid): X = 单糖，寡糖 Sphingolipids at cell surfaces are sites of biological recognition

  38. Phosphosphingolipids 鞘氨醇磷脂(Sphingomyelin 鞘磷脂) P.107 HO – CH – CH = CH – (CH2)12 – CH3 O Sphingosine (鞘氨醇) Fatty acid (脂肪酸) CH – NH –C – (CH2)14 – CH3 O CH2 – O –P – O – CH2 –CH2 –N+(CH3)3 O- Phosphocholine (磷酰胆碱) Sphinogomyelins are present in the plasma membranes of animal cells and are especially prominent in myelin, a membranous sheath that surrounds and insulates the axons of some neurons – thus the name “sphingomyelins”.

  39. 神经酰胺 Phosphosphinogolipid (鞘磷脂) (神经)鞘磷脂 Sphinogolipids 脑苷脂 Glycosphingolipids (鞘糖脂) 红细胞糖苷酯 神经节苷脂

  40. Glycosphingolipids as determinants of blood groups P.63 III. Structural Lipids Type O blood – universal donor Type AB blood – universal receiver

  41. Phospholipids and sphingolipids are degraded in lysosomes (细胞溶酶体) P.105 Phospholipase A1 H+, OH- O Phospholipase 磷脂酶 CH2 – O – C – R1 III. Structural Lipids O R2 – C – O – CH O H+, OH- CH2 – O – P – O – X O- Phospholipase A2 H+, Strong OH- H+ Phospholipase C Phospholipase D

  42. Sphingomyelins and gangliosides are degraded by a set of lysosomal enzymes. A genetic defect in any of these enzymes may lead to severe medical consequences.

  43. Fatal diseases related togenetic lipid storage disorder 鞘磷脂 鞘糖脂

  44. P.112 5. Sterols (甾醇) structural lipids present in the membranes of most eukaryotic cells Sterol’s roles Cholesterol (胆固醇) • Major constituents of plasma membrane and plasma lipoproteins (细胞质膜和脂蛋白的主要组成) • Precursors of other steroids (生成其它类固醇的前体) (牛磺胆酸) (胆汁酸) Cholesterol is the major sterol in animal tissues. Bacteria cannot synthesize sterols.

  45. Steroids derived from cholesterol(从胆固醇衍生出来的类固醇) 5 families of hormones Androgens (雄性激素) – testosterone (睾丸激素) Estrogens (雌激素) – estradiol (雌二醇) Progestins (孕激素) – progesterone (孕酮) Glucocorticoids (糖(肾上腺)皮质激素) – cortisol Mineralocorticoids (盐皮质激素) 睾丸激素 雌二醇 皮质(甾)醇 醛甾酮 肾上腺皮质激素 黄铜质 强的松 脱氢皮质(甾)醇

  46. IV. Active Lipids • Signals – e.g. Steroid hormones, vitamins A & D • Cofactors/electron carriers – e.g. coenzyme A, vitamins E & K • Pigments – e.g. -carotene (胡萝卜素) • A large group of volatile lipids produced in plants serve as signals passing through the air 角黄素 玉米黄质

  47. P.110 Terpenes and steroids(萜和类固醇) • Active lipids (活性脂质) • Unsaponifiable lipids (非皂化脂) • Different from other lipids: containing no fatty acids (不含脂肪酸) • Terpenes: composed of isoprene units (异戊二烯单位) • Steroids: composed of steroid nucleus (甾核) Zoosterol (动物固醇) Cholesterol (胆固醇) Sterols (甾醇) Phytosterol (植物固醇) -sitosterol (谷固醇)

  48. Terpenes (萜) Head-to-tail linkage P.110-112  Isoprene (C5) Tail-to-tail linkage Monoterpene (C10) – 单萜 Sesquiterpene (C15) – 倍半萜 Diterpene (C20) – 双萜 Tetraterpene (C40) – 四萜 Lycopene (C40, 番茄红素)

  49. Some biologically active isoprenoid compounds or derivatives 杀鼠灵 IV. Active Lipids 泛醌,辅酶Q 质体醌 长醇

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