膜结构及其转运功能

1、厦门大学医学院 戚 智Size of the cellsCell Diversity质膜成分质膜成分 (Composition of Plasma membrane)脂类脂类(Lipid)蛋白质蛋白质(Protein)少量糖类少量糖类(Carbohydrate) 如何用如何用最简单最简单的办法证明细胞膜是单分子层、的办法证明细胞膜是单分子层、双分子层还是多分子层结构？双分子层还是多分子层结构？如果把磷脂分子平铺在水如果把磷脂分子平铺在水面，其分子将如何分布？面，其分子将如何分布？液态镶嵌模型液态镶嵌模型Thickness 6nmSinger & Nicholson, 1972磷脂Pho

2、spholipids “water loving” “water fearing”（一）（一） 细胞膜的脂质细胞膜的脂质脂质分子种类脂质分子种类: : 磷脂磷脂(Phospholipid) (Phospholipid) ：70%70% 胆固醇胆固醇(Cholesterol)(Cholesterol)：30%30% 糖脂：糖脂： 10% 鞘脂鞘脂 ( (Sphingolipids ): ): 少量少量. .双嗜性分子（双嗜性分子（Amphipathic molecule）胆固醇（二）细胞膜的蛋白Membrane Proteins Proteins determine membranes spec

3、ific functions: Plasma membrane & organelle membranes each have unique collections of proteinsMembrane proteins:peripheral proteins(表面蛋白): reside outside hydrophobic region of lipids, loosely bound to surface of membraneintegral proteins （整合蛋白）: embedded within bilayer, usually across whole memb

4、rane transport proteinschannels, permeases (pumps)（三）细胞膜的糖类Membrane carbohydrates Play a key role in cell-cell recognition ability of a cell to distinguish one cell from another antigens important in organ & tissue development basis for rejection of foreign cells by immune systemGlycoprotein 糖蛋白

5、Glycolipid 糖脂Membrane Structure: Protein to Lipid Ratio varies from cell type to cell typeRatio for cells with high metabolic activity功能活跃的细胞，其膜蛋白含量较高 52%40%二、跨细胞膜的物质转运（一）单纯扩散（一）单纯扩散 Simple diffusion（二）易化扩散（二）易化扩散 （Facilitated diffusion） 1.经通道易化扩散经通道易化扩散（Facilitated diffusion via ion channel）2. 经载体的

6、易化扩散（Facilitated diffusion via carrier）(三三) 主动转运主动转运 （Active transport）(2）原发性主动转运；Primary active transport(3) 继发性主动转运；Secondary active transport（一）单纯扩散Simple Diffusion-Requires NO energyHigh speed;(10High speed;(106 610108 8/sec)/sec)Selectivity;Selectivity;G Gating. . 1. 1. 经通道易化扩散经通道易化扩散 ( (facili

7、tated diffusion via channel) GatingGating（门控）（门控）: : 1)Voltage-gated ion 1)Voltage-gated ion channelchannel 2)Chemically-gated 2)Chemically-gated ion channelion channel 3)Mechanically-gated 3)Mechanically-gated ion channelion channel离子通道的门控特性示意图2. 经载体易化扩散经载体易化扩散 Facilitated diffusion via carrier转运物质

8、:水溶性小分子物质,如葡萄糖（右旋）、AA、核苷酸经载体易化扩散的特点经载体易化扩散的特点： 顺浓度差顺浓度差转运转运, ,速度比依溶质物理特性预期的快速度比依溶质物理特性预期的快( (move solutes faster across membrane); ; 饱和现象饱和现象(saturation); 结构特异性结构特异性 (highly specific to specific solutes); 竞争抑制竞争抑制competitive inhibition米氏常数米氏常数（三）主动转运（三）主动转运 active transport定义细胞膜通过本身某种耗能过程，借助细胞膜某些蛋细胞

9、膜通过本身某种耗能过程，借助细胞膜某些蛋白质的帮助，将非脂溶性物质分子或离子白质的帮助，将非脂溶性物质分子或离子逆电化学梯度逆电化学梯度差差进行的转运。进行的转运。 根据转运能量是否直接来源于根据转运能量是否直接来源于ATPATP的不同分为的不同分为: :原发原发和继发两种主动转运形式。和继发两种主动转运形式。钠-钾泵 sodium-potassium pump简称钠泵sodium pump,又称Na+-K+-ATP酶(Na+-K+-ATPase)1. 原发性主动转运 Primary Active Transport胞内高钾胞内高钾, ,为代谢提供必需条件为代谢提供必需条件（e.g.,e.g.

10、,核糖体合成蛋白）核糖体合成蛋白）; ;维持胞质渗透压和细胞容积的稳维持胞质渗透压和细胞容积的稳定定; ;是细胞产生生物电的前提条件；是细胞产生生物电的前提条件；生电性生电性( (排出排出3Na3Na+ +, ,转入转入2K2K+ +) )作用作用, ,增大膜内负电位增大膜内负电位, ,影响静息电位的影响静息电位的数值；数值；建立钠的跨膜浓度梯度，为继发建立钠的跨膜浓度梯度，为继发性主动转运提供动力（性主动转运提供动力（NaNa+ +-H-H+ +交交换，换， NaNa+ +-Ca-Ca2+2+交换）。交换）。钠泵（钠钾泵）活动的生理意义同向转运体同向转运体（ 反向转运体反向转运体（ 2.2.

11、继发性主动转运继发性主动转运(secondary active transport) 某物质逆差转运某物质逆差转运( (主动转运主动转运) )所需的能量不直接来自所需的能量不直接来自ATPATP的分解的分解, ,而而是来自另一物质主动转运形成的势能贮备是来自另一物质主动转运形成的势能贮备( (主要是钠泵活动形成的主要是钠泵活动形成的NaNa+ +在膜两侧的浓度势能差在膜两侧的浓度势能差) )。（1）同向转运近端肾小管上皮 （Na+-Glucose）小肠黏膜上皮（2Na+-Glucose）Na+-氨基酸氨基酸肾小管上皮细胞肾小管上皮细胞肾小管上皮细胞肾小管上皮细胞甲状腺上皮细胞甲状腺上皮细胞（1

12、）反向转运Exchangers (also known as antiporters) are found in many different cells and tissues and perform a variety of important physiological functions. Three examples are shown here. 肠黏膜上皮细胞葡萄糖继发性主动转运模式图肠黏膜上皮细胞葡萄糖继发性主动转运模式图How about large molecules? Moving large molecules into & out of cell throug

13、h vesicles 消耗能量、主动 Exocytosis-出胞 = the movement of a substance by a vesicle to the outside of a cell Constitutive Exocytosis-持续性出胞 Regulated Exocytosis-调节性出胞 endocytosis 入胞= the movement of a substance into a cell by a vesicle phagocytosis 吞噬= “cellular eating” Pinocytosis-吞饮 = “cellular drinking”（四

14、）膜泡运输 （Vesicular transport）30Inside CellCell environment31copyright cmassengaleExocytosis: regulated and constitutive secretion. During secretion, vesicles derived from the trans face of the Golgi complex will fuse with the plasma membrane, dumping their contents into the extracellular environment.

15、In constitutive secretion, secretory vesicles are continuously delivered to the plasma membrane, where they rapidly fuse with the membrane. In regulated secretion, the vesicles derived from the trans face of the Golgi complex aggregate and concentrate their contents in the cytoplasm, where they rema

16、in until the cell has received the appropriate signal. Then, the secretory vesicles fuse with the plasma membrane. The contents of these two classes of secretory vesicles are distinct.（1）持续性出胞）持续性出胞 Constitutive Exocytosis （2）调节性出胞）调节性出胞 Regulated Exocytosis例：小肠黏膜杯状细胞分泌黏液例：小肠黏膜杯状细胞分泌黏液例：动作电位达到神经末梢引起

17、神经递质的释放例：动作电位达到神经末梢引起神经递质的释放(Cell eating)2. 入胞（入胞（Endocytosis）34copyright cmassengale（2）吞饮 (Pinocytosis)受体介导的入胞受体介导的入胞Receptor-mediated endocytosis液态镶嵌模型双噬性分子磷脂胆固醇表面蛋白整合蛋白单纯扩散易化扩散离子通道离子选择性化学门控通道电压门控通道机械门控通道水通道转运体载体主动转运钠-钾泵钙泵被动转运继发性主动转运同向转运体反向转运体交换体膜胞转运出胞入胞吞噬吞饮受体介导入胞液态镶嵌模型液态镶嵌模型Thickness 6nmSinger &a

18、mp; Nicholson, 1972二、跨细胞膜的物质转运（一）单纯扩散（一）单纯扩散 Simple diffusion（二）易化扩散（二）易化扩散 （Facilitated diffusion） 1.经通道易化扩散经通道易化扩散（Facilitated diffusion via ion channel）2. 经载体的易化扩散（Facilitated diffusion via carrier）(三三) 主动转运主动转运 （Active transport）(2）原发性主动转运；Primary active transport(3) 继发性主动转运；Secondary active tra

19、nsportHigh speed;(10High speed;(106 610108 8/sec)/sec)Selectivity;Selectivity;G Gating. . 1. 1. 经通道易化扩散经通道易化扩散 ( (facilitated diffusion via channel)31copyright cmassengaleExocytosis: regulated and constitutive secretion. During secretion, vesicles derived from the trans face of the Golgi complex will fuse with the plasma membrane, dumping their contents into the extracellular environment. In cons