脂质Lipid

脂质不是按共同结构而是按溶解性定义的。简单脂质由脂肪酸与醇构成（甘油三酯、蜡）；复合脂质还含磷酸或糖（磷脂、糖脂），具有亲水的“头”和疏水的“尾”，是两亲分子；衍生脂质包括类固醇（胆固醇、性激素）、脂溶性维生素（A、D、E、K）和类二十烷酸（前列腺素）。现代脂质组学把脂质分为 8 大类。

Lipids are defined by solubility rather than by a shared structure. Simple lipids are esters of fatty acids with alcohols (triglycerides, waxes); complex lipids also contain phosphate or sugar (phospholipids, glycolipids) and are amphipathic, with a hydrophilic head and hydrophobic tails; derived lipids include steroids (cholesterol, sex hormones), fat-soluble vitamins (A, D, E, K) and eicosanoids such as prostaglandins. Modern lipidomics divides lipids into eight categories.

1813–1823 年谢弗勒尔研究油脂皂化，发现脂肪由脂肪酸和甘油组成，并分离出硬脂酸、油酸等。1847 年戈布利从蛋黄中分离出卵磷脂。1925 年戈特和格伦德尔提出细胞膜是脂双层，1972 年辛格和尼科尔森提出流动镶嵌模型，至今仍是生物膜结构的基本模型。

Between 1813 and 1823 Chevreul studied the saponification of fats, showed they consist of fatty acids and glycerol, and isolated stearic and oleic acids. Gobley isolated lecithin from egg yolk in 1847. Gorter and Grendel proposed in 1925 that cell membranes are lipid bilayers, and Singer and Nicolson's fluid mosaic model of 1972 is still the basic model of membrane structure.

每克脂肪完全氧化约释放 38 kJ 能量，是糖和蛋白质的两倍多，因而是高效的储能形式。磷脂在水中自发形成双层膜，把细胞与环境隔开。类固醇激素和类二十烷酸调节代谢、炎症和生殖。血液中脂质以脂蛋白形式运输，低密度脂蛋白胆固醇过高是动脉粥样硬化的危险因素。

Fat yields about 38 kJ per gram when fully oxidised, more than twice as much as carbohydrate or protein, making it an efficient energy store. Phospholipids spontaneously form bilayers in water, separating the cell from its surroundings. Steroid hormones and eicosanoids regulate metabolism, inflammation and reproduction. Lipids travel in the blood as lipoproteins, and high LDL cholesterol is a risk factor for atherosclerosis.