1、 第二章 细胞的基本功能第一节细胞膜的结构和物质转运功能Size of the cellsCell Diversity细胞是组成人体和其他生物体的基本结构和功能单位细胞是组成人体和其他生物体的基本结构和功能单位质膜成分质膜成分 (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)Thickness 6nm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%鞘脂
2、鞘脂 (Sphingolipids):):少量少量.Phospholipids “water loving”“water fearing”如果把磷脂分子平铺在水面，其分子将如何分布？如果把磷脂分子平铺在水面，其分子将如何分布？如何用如何用最简单最简单的办法证明细胞膜的双分子层结构？的办法证明细胞膜的双分子层结构？Phospholipid bilayerpolarhydrophilicheadsnonpolarhydrophobictailspolarhydrophilicheadsFor more on this history,see:http:/www1.umn.edu/ships/9-2
3、/membrane.htm液态镶嵌模型液态镶嵌模型Thickness 6nm膜的流动性：不饱和脂肪酸含量胆固醇含量蛋白含量Arctic fish,Thymallus arcticus细胞膜上含有大量的不饱和脂肪酸细胞膜的不对称性细胞膜的不对称性Membrane ProteinsProteins determine membranes specific functions:Plasma membrane&organelle membranes each have unique collections of proteinsMembrane proteins:peripheral proteins
4、:reside outside hydrophobic region of lipids,loosely bound to surface of membraneintegral proteins:embedded within bilayer,usually across whole membrane transmembrane proteintransport proteinschannels,permeases(pumps)Glycoprotein 糖蛋白Glycolipid 糖脂The four human blood groups(A,B,AB,and O)differ in the
5、 external carbohydrates on red blood cells.(B)Binding of B subunits to oligosaccharide of GM1 ganglioside.(A)Cholera toxin approaching target cell surface.(C)Conformational alteration of holotoxin presenting A subunit(black)to cell surface.细胞细胞-膜包围和分割的系统膜包围和分割的系统52%40%OutsidePlasmamembraneInsideTran
6、sporterCell surfacereceptorEnzymeactivityCell surface identity markerAttachment to thecytoskeletonCell adhesionThis illustrates simple passive diffusion物质的跨膜转运（一）单纯扩散（一）单纯扩散 Simple diffusion（二）膜蛋白介导的跨膜转运（二）膜蛋白介导的跨膜转运 Membrane protein mediated transport1.通道介导的跨膜转运通道介导的跨膜转运；Facilitated diffusion via i
7、on channel2.载体介导的跨膜转运；(1)经载体的易化扩散；Facilitated diffusion via carrier(2）原发性主动转运；Primary active transport(3)继发性主动转运；Secondary active transportSimple Diffusion Across BilayersPassive diffusion-unaided by transport proteins-no metabolic energy expended-movement is down chemical concentration gradient-dif
8、fusion rate is proportional to concentration gradient and hydrophobicity-rate limiting step is movement across hydrophobic portion of membrane-the greater the hydrophobicity of a water-soluble molecule,the faster it diffuses across phospholipid bilayer.High speed;(10High speed;(106 610108 8/sec)/sec
9、)Selectivity;Selectivity;G Gating.1.1.通道介导的跨膜转运通道介导的跨膜转运 (facilitated diffusion via channel)Membrane protein mediated transportPumps =100-103Carriers =102-104Channels=107-108(ions/sec)(carriers)2.载体介导的跨膜转运载体介导的跨膜转运 (1)经载体易化扩散经载体易化扩散 Facilitated diffusion via carrier转运物质转运物质:小分子物质小分子物质,如如AA、核苷酸、核苷酸Un
10、iporterUniporter 单物质转运体单物质转运体 Membrane protein mediated transport转运体转运体 transporter：同向转运体同向转运体（反向转运体反向转运体（定义定义细胞膜通过本身某种耗能过程，借助细胞膜某些蛋白质细胞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逆电化学梯度差进行的帮助，将非脂溶性物质分子或离子逆电化学梯度差进行的转运。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:原发和继原发和继发两种主动转运形式。发两种主动转运形式。（2）原发性主动转运）原发
11、性主动转运 Primary Active TransportTransport of a substance across the cell membrane against its concentration gradientMolecules move from a lower concentration to a higher concentrationRequires the cells to use energy(ATP)Primary active transport钠钠-钾泵钾泵 sodium-potassium pump简称钠泵简称钠泵sodium pump,又称又称Na+-K
12、+-ATP酶酶(Na+-K+-ATPase)3Na+(由胞内向胞外由胞内向胞外):2K+(由胞外向胞内由胞外向胞内)Sodium Potassium Pumps钠-钾泵工作原理Transports 3 sodium ions (Na+)out of the cell and 2 potassium ions(K+)into the cellNa+concentration is higher outside the cellK+concentration is higher inside the cellIons move against their concentration gradien
13、tATP is neededWhy is this sodium-potassium pump so important for animal cells?Ouabain(哇巴因)increased Na+conc inside heart leads to stimulation of Na+-Ca2+exchanger,which extrudes sodium in exchange for inward movement of calcium.Increased intracellular Calcium stimulates muscle contraction.Maintains
14、low cytosolic Ca+Present In Plasma and ER membranes Model for mode of action for Ca+ATPase Conformation change（3 3）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的的分解分解,而是来自另一物质主动转运形成的势能贮备而是来自另一物质主动转运形成的势能贮备(主要主要是钠泵活动形成的是钠泵活动形成的NaNa+在膜两侧的浓度势能差在膜两侧的浓度势能差)
15、。肠黏膜上皮细胞葡萄糖继发性主动模式图转运肠黏膜上皮细胞葡萄糖继发性主动模式图转运simplediffusionfacilitateddiffusionactivetransportATP+钠-钾泵建立了细胞内外的钠、钾离子浓度差。胞外钠离子利用钠离子的浓度差由细胞外进入细胞内是否是继发性主动转运？How about large molecules?Moving large molecules into&out of cellthrough vesiclesendocytosis=the movement of a substance into a cell by a vesicle phag
16、ocytosis=“cellular eating”pinocytosis=“cellular drinking”exocytosis=the movement of a substance by a vesicle to the outside of a cell Endocytosis(Cell eating)53copyright cmassengale吞饮作用吞饮作用(Pinocytosis-Cell drinking)受体介导的入胞示意图受体介导的入胞示意图57Inside CellCell environment58copyright cmassengaleATP物质的跨膜转运（一）单纯扩散（一）单纯扩散 Simple diffusion（二）膜蛋白介导的跨膜转运（二）膜蛋白介导的跨膜转运 Membrane protein mediated transport1.通道介导的跨膜转运通道介导的跨膜转运；Facilitated diffusion via ion channel2.载体介导的跨膜转运；(1)经载体的易化扩散；Facilitated diffusion via carrier(2）原发性主动转运；Primary active transport(3)继发性主动转运；Secondary active transport谢谢！
