532生物膜的化学组成及其在膜中的结构 所有生物膜都是类脂一蛋白质聚合体( lipid- protein assemblies),膜成分主要是通过共价结合组装成薄的片层结 构。除了类脂和蛋白质,大多数生物膜还含有某些糖类化合物 膜上含有结合状态的结构水,并存在与某些膜蛋白结合的金属 离子。不仅在原核细胞与真核细胞之间,不同组织类型(如肌 肉、肝脏、软骨等等)的细胞之间,而且在不同细胞器(质膜 内质网、高尔基体等等)的膜之间,膜蛋白与膜脂的比例变动 是相当大的。这样的差别是与各种膜执行其特殊功能密切相关 的。例如线粒体内膜含有电子传递链的蛋白载体,其膜蛋白的 比例较之其他膜要高得多。神经髓鞘在神经纤维外造成电绝缘 层,它由厚厚的高电阻的脂质层构成,仅含少量的蛋白质 All membranes are lipid-protein assemblies holding together in a thin sheet by mainly non-covalent bonds. They also contain carbohydrates. The ratio of lipid to protein varies considerably depending on the type of cellular membrane, the type of organism, and the type of cells
5.3.2 生物膜的化学组成及其在膜中的结构 所有生物膜都是类脂—蛋白质聚合体（1ipid-protein assemblies），膜成分主要是通过非共价结合组装成薄的片层结 构。除了类脂和蛋白质，大多数生物膜还含有某些糖类化合物。 膜上含有结合状态的结构水，并存在与某些膜蛋白结合的金属 离子。不仅在原核细胞与真核细胞之间，不同组织类型（如肌 肉、肝脏、软骨等等）的细胞之间，而且在不同细胞器（质膜、 内质网、高尔基体等等）的膜之间，膜蛋白与膜脂的比例变动 是相当大的。这样的差别是与各种膜执行其特殊功能密切相关 的。例如线粒体内膜含有电子传递链的蛋白载体，其膜蛋白的 比例较之其他膜要高得多。神经髓鞘在神经纤维外造成电绝缘 层，它由厚厚的高电阻的脂质层构成，仅含少量的蛋白质。 All membranes are lipid-protein assemblies holding together in a thin sheet by mainly non-covalent bonds. They also contain carbohydrates. The ratio of lipid to protein varies considerably depending on the type of cellular membrane, the type of organism, and the type of cells
表5.1膜的化学组成(%) 膜的类别 蛋白质 脂类 糖类 蛋白质/脂类 髓鞘 18 79 0.23 质膜 血小板33-4250-51 7.5 人工红细胞49 43 1.0 大鼠肝细胞46 5-10) 0.9 盐杆菌紫膜75 25 内质网膜67 33 2.0 线粒体内膜76 24 (1-2) 菠菜叶绿体片层70 30 0
表 5.1 膜的化学组成（％） 膜的类别 蛋白质 脂类 糖类 蛋白质/脂类 髓鞘 18 79 3 0.23 质膜 血小板 33－42 50－51 7.5 人工红细胞 49 43 8 1.0 大鼠肝细胞 46 42 （5－10） 0.9 盐杆菌紫膜 75 25 0 内质网膜 67 33 2.0 线粒体内膜 76 24 （1－2） 3.2 菠菜叶绿体片层 70 30 0
5.3.2.1 The composition of membrane lipids Phospholipid posphoglycerides( PC, ps, pl, pe, cl etc. sphingolipids Glycolipids neutralglycolipids(cerebroside etc.) acidid glycolipids( gangliosides etc. glyceroglycolipids Cholesterol There are 50% of lipid molecules, 5x106/H 2 10/per cell in the plasma membrane in some animal ceus
5.3.2.1 The composition of membrane lipids Phospholipid posphoglycerides( PC, PS, PI, PE, Cl etc.) sphingolipids Glycolipids neutralglycolipids(cerebroside etc.) acidid glycolipids(gangliosides etc.) glyceroglycolipids Cholesterol There are ~50% of lipid molecules, 5x106 /μ2 , 109 /per cell in the plasma membrane in some animal cells
(a) PHOSPHOLIPIDS Phosphatidyicholine (shown) Phosphate Glycerol Diphosphatidylglycerol (cardiolipin) 副圈 Cholin Sphingomyelin(a sphingolipid) Phosphate b) GLYCOLIPIDS Cerebrosides (galactocerebroside shown) (c) STEROLS ol (shown) Sitosterol
不4 8 OOOOOOX (a) Cholesterol in plasma membrane a)Lipids with saturated fatty acids pack together well in (b)Lipids with a mixture of saturated and unsaturated fatty (b) Bonding of cholesterol to phospholipid acids do not pack together well in the membrane Figure 7-15 Orientation of Cholesterol Molecules in a Lipid Figure 7-14 The Effect of Unsaturated Fatty Acids on the Packing Bilayer. (a)Cholesterol molecules are present in both lipid layers in of Membrane Lipids. (a) Membrane phospholipids with no unsaturated the plasma membranes of most animal cells, but a specific molecule is fatty acids fit together tightly because the fatty acid chains are parallel to localized to one of the two layers. (b) Each molecule orients itself in th each other(b)Membrane lipids with one or more unsaturated fatty acids pid layer so that its single hydroxyl group is close to the polar head do not fit together as tightly because the cis double bonds cause bends in group of a neg boring phospholipid molecule, where it forms a hydrogen the chains, which interfere with packing. Each of the structures shown is a bond with the oxygen of the ester bond between the glycerol backbone phosphatidylcholine molecule, with either two 18-carbon saturated fatty and a fatty acid. The steroid rings and hydrocarbon side group of the acids(stearate) (part a) or two 18-carbon fatty acids, one saturated cholesterol molecule interact with adjacent hydrocarbon chains of the (stearate)and the other with one double bond (oleate(part b) membrane phospholipids