8.lipids

  • 基础
    • Lipids are a class of biological molecules defined by low solubility in water and high solubility in nonpolar solvents.
      脂质是一类生物分子，其定义为在水中溶解度低，而在非极性溶剂中溶解度高
    • As molecules that are largely hydrocarbon 烃 in nature, lipids represent highly reduced forms of carbon and,upon oxidation in metabolism, yield large amounts of energy.
      由于脂质本质上多为烃类分子，属于碳的高度还原形式，因此在代谢过程中发生氧化时，会产生大量能量
    • Lipids are thus the molecules of choice for metabolic energy storage.
    • The lipids found in biological systems are either hydrophobic 疏水(containingonly nonpolar groups) or amphipathic 两性分子的, which means they possess both polar and nonpolar groups.
    • The hydrophobic nature of lipid molecules allows membranes to act as effective barriers to more polar molecules.
  • Fatty Acids
    • basic
      • A fatty acid is composed of a long hydrocarbon 烃 chain (tail) and a terminal carboxyl group 羧基 (head).
      • The carboxyl group is normally ionized under physiological conditions.
        羧基在生理条件下通常会发生电离
      • Fatty acids occur in large amounts in biological systems, but rarely in the free, uncomplexed state. They typically are esterified to glycerol or other backbone structures.
        脂肪酸在生物系统中大量存在，但很少以游离、未结合的状态存在, 它们通常会与甘油或其他骨架结构发生酯化反应
    • 饱和与不饱和脂肪酸

      • 只要有双键的都是不饱和
    • Good and Bad fatty acid in food
      • Lower both the saturated 饱和脂肪酸 and trans fatty acids 反式脂肪酸 in diets can help to reduce the risk of coronary heart disease 冠心病
      • 顺式脂肪酸和反式脂肪酸
      • Margarines人造黄油
        • 原料 oils composition includes greater than 50% unsaturated fatty acids
        • Hydrogenation is the addition of hydrogen to double-bonds producing a saturated hydrocarbon
        • 人造黄油氢化导致饱和脂肪酸变多, 不健康
      • polyunsaturatedfatty acids (PUFA) 多不饱和脂肪酸
        • Fish oil- Omega-3 fatty acid-DHAand EPA, DPA
  • Triacylglycerols 甘油三酯
    • A significant number of the fatty acids in plants and animals exist in the form of triacylglycerols(also called triglycerides)
    • These molecules consist of a glycerol甘油,丙三醇 esterified with three fatty acids
    • Triacylglycerols are a major energy storage and the principal neutral derivatives of glycerol found in animals
      甘油三酯是主要的能量储存物质，也是动物体内发现的甘油的主要中性衍生物
    • Triacylglycerols are rich in highly reduced carbons and thus yield large amounts of energy in the oxidative reactions of metabolism
    • Triacylglycerols in animals are found primarily in the adipose tissue (body fat)
  • Glycerophospholipids 甘油磷脂
    • A 1,2-diacylglycerol that has a phosphate group esterified at carbon atom 3 of the glycerol backbone is a glycerophospholipid
    • also known as a phosphoglyceride磷酸甘油酯 or a glycerol phosphatide甘油磷脂
    • They are essential components of cell membranes and are found in small concentrations in other parts of the cell.
    • All glycerophospholipids are members of the broader class of lipids known as phospholipids
  • phospholipids 磷脂
    • common phospholipids
      • Glycerophospholipids 甘油磷脂
      • phosphatidylcholine卵磷脂(knownas lecithin) and phosphatidylethanolamine, are two of the most common constituents of biological membranes
      • diphosphatidylglycerol is another kind of glycerol phosphatide found in many tissues. First observed in heart tissue, it is also called cardiolipin
    • Degradation
      • The venoms 毒液 of poisonous snakes contain (among other things) a class of enzymes known as phospholipases 磷脂酶, enzymes that cause the breakdown of phospholipids
      • The phospholipid breakdown product of this reaction, lysolecithinlysolecithin 溶血卵磷脂, acts as a detergent and dissolves the membranes of red blood cells,causing them to rupture
        该反应的磷脂分解产物 , 溶血卵磷脂，具有去污剂样作用，能溶解红细胞膜，导致红细胞破裂
  • Sphingolipids 神经鞘脂类
    • Sphingolipids represent another class of lipids found frequently in biological membranes
    • An 18-carbon amino alcohol, sphingosine 鞘氨醇, forms the backbone of these lipids
    • Typically, a fatty acid is joined to a sphingosine via an amide linkage to form a ceramide 神经酰胺
    • 角质层中40%~50%的皮脂由神经酰胺构成
    • Sphingomyelins (神经)鞘磷脂
      • represent a phosphorus-containing subclass of sphingolipids and are especially important in the nervous tissue of higher animals
      • A sphingomyelin is formed by the esterification of a phosphorylcholine 磷酸胆碱 or a phosphorylethanolamine 磷酸乙醇胺 to the 1-hydroxy group of a ceramide
    • glycosphingolipids 鞘糖脂
      • are another class of ceramide-based lipids that are important components of muscle and nerve membranes in animals
      • They consist of a ceramide with one or more sugar residues in a glycosidic linkage at the 1-hydroxyl moiety

        • 它们由神经酰胺（ceramide）构成，在神经酰胺的 1 - 羟基部分（1-hydroxyl moiety）通过糖苷键（glycosidic linkage）连接了一个或多个糖残基（sugar residues）
  • Waxes
    • Waxes are esters of long-chain alcohols withlong-chain fatty acids.
      蜡是长链醇与长链脂肪酸形成的酯类
    • The resulting molecule can be viewed (in analogy to the glycerolipids) as having a weakly polar head group (the ester moiety itself) and a long, nonpolar tail (the hydrocarbon chains).

      • 生成的分子（可类比甘油脂）可看作具有一个弱极性的头部基团（即酯基本身）和一条长的非极性尾部（即烃链）
    • Fatty acids found in waxes are usually saturated.
      蜡中含有的脂肪酸通常是饱和的
    • The alcohols found in waxes may be saturated or unsaturated and may include sterols, such as cholesterol 胆固醇
      蜡中含有的醇类则可能是饱和的，也可能是不饱和的，还可能包含固醇类物质，例如胆固醇
    • Waxes are water-insoluble due to the weakly polar nature of the ester group.
    • As a result, this class of molecules confers water-repellant character to animal skin, to the leaves of certain plants, and to bird feathers.
  • Terpenes 萜tie类
    • The terpenes are a class of lipids formed from combinations of two or more molecules of 2-methyl-1,3-butadiene 丁二烯, better known as isoprene 异戊二烯 (a five-carbon unit that is abbreviated C5).

      • 萜烯是一类脂质，由两个或多个 2 - 甲基 - 1,3 - 丁二烯 (即丁二烯) 分子组合形成，这种分子更广为人知的名称是异戊二烯 ( 一种含 5 个碳原子的结构单元，缩写为 C5)
    • A monoterpene (C10) consists of two isoprene units, a sesquiterpene倍半萜烯 (C15) consists of three isopreneunits, a diterpene二萜 (C20) has four isoprene units, and so on.
      单萜由两个异戊二烯单元构成，倍半萜烯由三个异戊二烯单元构成，二萜由四个异戊二烯单元构成，以此类推
    • Isoprene units can be linked in terpenes to form straight chain or cyclic molecules, and the usual method of linking isoprene units is head to tail

      • 萜烯中的异戊二烯单元可通过连接形成直链或环状分子，而异戊二烯单元常见的连接方式是 “头对尾” 连接
    • Triterpenes (三萜烯) are C30 terpenes and include squalene(角鲨烯) and lanosterol(羊毛甾醇), two of the precursors of cholesterol (胆固醇) and other steroids(类固醇)
    • Tetraterpenes, C40
      • carotenoids(类胡萝卜素),a class of colorful photosynthetic pigments
      • beta-Carotene(胡萝卜素) is the precursor of vitamin A
      • whilelycopene (番茄红素),similar to beta-carotene but lacking the cyclopentene rings, is a pigment found in tomatoes
  • Steroids 类固醇
    • A large and important class of terpene-based lipids is the steroids.
    • This molecular family, whose members effect an amazing array of cellular functions, is based on a common structural motif of three six-membered rings and one five-membered ring all fused together.
      这类分子家族的成员能实现种类繁多的细胞功能，其结构基础是一个共同的结构母核 —— 由三个六元环和一个五元环全部稠合而成
    • Cholesterol 胆固醇
      • the most common steroid in animals and the precursor for all other animal steroids
      • functions
        • Cholesterolis a principal component of animal cell plasma membranes, and much smaller amounts of cholesterol are found in the membranes of intracellular organelles, eg.ER.
        • The relatively rigid fused ring system of cholesterol and the weakly polar alcohol group at the C-3 position have important consequences for the properties of plasma membranes.
          胆固醇中相对刚性的稠环系统，以及其 C-3 位上弱极性的羟基，对质膜的特性有着重要影响
        • Cholesterol is also a component of lipoprotein 脂蛋白 complexes in the blood, and it is one of the constituents of plaques斑块 that form on arterial动脉walls in atherosclerosis 动脉硬化症.
          胆固醇也是血液中脂蛋白复合物的组成成分之一，同时它还是动脉硬化症中动脉壁上形成的斑块的组成成分之一
    • Steroid Hormones 类固醇激素
      • Steroids derived from cholesterol in animals include five families of hormones
        • androgens 雄激素
        • estrogens 雌激素
        • progestins 孕酮, 黄体酮
        • glucocorticoids 糖(肾上腺)皮质激素
        • mineralocorticoids盐皮质激素
      • bile acids 胆酸
        不算激素,但是结构类似
      • 结构
    • Plant Sterols
      • 图
      • 为了减少 cholesterol 胆固醇摄入可以 consuming the plant sterols (phytosterols) 植物固醇
      • although plant sterols are not effectively absorbed by the body, they nonetheless are highly effective in blocking the absorption of cholesterol itself by intestinal cells through competition - Functional Food
        虽然植物固醇无法被人体有效吸收，但它们仍能通过竞争作用，高效阻断肠道细胞对胆固醇本身的吸收 — 这属于功能性食品的范畴