5cyj1plasmamembrane

1、Plasma Membranes: Their Structure, Chemistry and Functions Unit 5Outline History of studies on membrane structure Chemical composition of membranes Through the membranes 生物膜生物膜 (Biomembrane) 细胞质膜细胞质膜 (Plasma Membrane) 细胞内膜细胞内膜 (Endomembrane ) 细细胞胞的的生生物物膜膜体体系系Outline History of studies on membrane st

2、ructure Chemical composition of membranes Through the membranes 1890sEight milestonesMilestone 11890s OvertonLipid nature of membraneMilestone 21900s LangmuirLipid monolayerMilestone 31925 Gorter & GrendelLipid bilayerMilestone 41935 Davson & Danielli“Sandwich model”Milestone 51959 RobertsonUnit mem

3、brane modelMilestone 61972 Singer & NicolsonFluid mosaic model流动镶嵌模型流动镶嵌模型Fluid-mosaic model was proposed in 1972 by S. Jonathan Singer and Garth Nicolson;The structure and arrangement of membrane proteins in the fluid-mosaic model differ from that of previous models in that they occur as a “mosaic

4、of discontinuous particles that penetrate the lipid sheet; Most importantly, the fluid-mosaic model presents cellular membranes as dynamic structures 动态结构动态结构in which the components are mobile and capable of coming together to engage in various types of transient or semipermanent interactions. 流动镶嵌模

5、型流动镶嵌模型(Fluid mosaic model)The Fluid Mosaic ModelFluid mosaic modelMilestone 7Late 1970s Unwin & HendersonMembrane protein structureMembrane protein structureLate 1970s Unwin & HendersonMilestone 81990s K.Simons et al.Lipid rafts model (lipid rafts model) (lipid rafts model)1988年年,美美Simon提出。提出。存在于绝大

6、多数哺乳动物质膜和部分内膜系统。存在于绝大多数哺乳动物质膜和部分内膜系统。特征特征：脂筏脂筏与与质膜微囊质膜微囊（caveolae），又称，又称去污剂不溶的富含糖脂区去污剂不溶的富含糖脂区（detergent-resistant fraction）.主要含有鞘脂和胆固醇而呈现介于液晶相和凝主要含有鞘脂和胆固醇而呈现介于液晶相和凝胶相之间的胶相之间的液态有序相液态有序相（liquid-ordered phase）或或Lo相。以相。以Lo相为特征的脂质相为特征的脂质微区四周被流动的、液态无序相的脂质分子包围，犹如很多小筏漂浮在流动的脂微区四周被流动的、液态无序相的脂质分子包围，犹如很多小筏漂浮在流

7、动的脂质海洋中。质海洋中。约约70nm70nm左右，是一种动态结构，位于质膜的外小页。左右，是一种动态结构，位于质膜的外小页。主要功能：主要功能：信号转导、膜的运送（内吞、外排），胆固醇运送、维持胞内信号转导、膜的运送（内吞、外排），胆固醇运送、维持胞内CaCa2+2+稳态平衡、蛋白分选等。稳态平衡、蛋白分选等。 Typical plasma Membrane Outline History of studies on membrane structure Chemical composition of membranes Through the membranes 2. Chemical C

8、omposition of MembranesMembrane LipidsMembrane CarbohydratesMembrane ProteinsA. Membrane LipidsPhospholipids磷脂磷脂Glycolipids糖脂糖脂Sterols固醇类固醇类2. The chemical composition of membranesMembranes contain a wide diversity of lipids, all of which are amphipathic两亲性的两亲性的; that is, they contain both hydrophil

9、ic 亲水性亲水性and hydrophobic疏水性疏水性 regions. 2.1 Membrane Lipids亲水头部亲水头部疏水尾部疏水尾部磷脂分子磷脂分子2. The chemical composition of membranes There are three main types of membrane lipids: Phospholipid 磷脂磷脂 Cholesterol 胆固醇；胆固醇； Glycolipids 糖脂糖脂。2.1 Membrane LipidsPhospholipids磷酸磷酸胆碱胆碱甘油甘油磷酸磷酸极性亲水头部极性亲水头部非极性疏水尾部非极性疏水尾

10、部胆固醇胆固醇Movement of Membrane Lipids Liposome脂质体脂质体 A. Study on nature性质研究性质研究B. Gene transfer 基因导入基因导入C. Carrier载体载体 Type Application B. Membrane ProteinsIntegral proteinsPeripheral proteinsLipid-anchored proteins脂锚定蛋白脂锚定蛋白Integral proteins整合蛋白整合蛋白Peripheral proteins外周蛋白外周蛋白2.2 Membrane proteins 生物膜的

11、特定功能主要是由蛋白质完成的；生物膜的特定功能主要是由蛋白质完成的；膜蛋白约占膜的膜蛋白约占膜的40%40%50%, 50%, 有有5050余种膜蛋白；余种膜蛋白；在不同细胞中膜蛋白的种类及含量有很大差异。有在不同细胞中膜蛋白的种类及含量有很大差异。有的含量不到的含量不到25%25%，有的达到，有的达到75%75%；一般来说一般来说, ,功能越复杂的膜，其上的蛋白质含量越功能越复杂的膜，其上的蛋白质含量越多，种类越多。多，种类越多。整合蛋白整合蛋白(Integral Proteins) 部分或全部镶嵌部分或全部镶嵌在细胞膜中或内外两侧的蛋白质；在细胞膜中或内外两侧的蛋白质； In fact,

12、all integral proteins are probably transmembrane proteins; that is, they pass entirely through the lipid bilayer and thus have domains that protrude from both the extracellular and cytoplasmic sides of the membrane ；根据跨膜次数将跨膜蛋白分为单次跨膜、多次跨膜、多根据跨膜次数将跨膜蛋白分为单次跨膜、多次跨膜、多亚单位跨膜等；跨膜蛋白的跨膜区为一般为亚单位跨膜等；跨膜蛋白的跨膜区为一

13、般为螺旋螺旋, , 也也有的是有的是折叠，如孔蛋白；折叠，如孔蛋白；整合蛋白约占膜蛋白的整合蛋白约占膜蛋白的70-80%70-80%。The types of membrane proteinsIntegral ProteinsProteins are located entirely outside of the lipid bilayer, on the cytoplasmic or extracellular side, yet are associated with the surface of the membrane by noncovalent bonds.外周蛋白为水溶性；外周

14、蛋白为水溶性；占膜蛋白总量的占膜蛋白总量的20%20%30%30%，在红细胞中占，在红细胞中占50%50%，如红，如红细胞的血影蛋白和锚定蛋白都是外周蛋白。细胞的血影蛋白和锚定蛋白都是外周蛋白。外周蛋白外周蛋白(peripheral proteins)Peripheral ProteinsProteins that are located outside the lipid bilayer, on either the extracellular or cytoplasmic surface, but are covalently linked to a lipid molecule that

15、 is situated within the bilayer;又称脂连接蛋白又称脂连接蛋白(lipid-linked proteins)，同脂的结同脂的结合有两种方式：合有两种方式：一种方式是通过一个糖分子间接同脂双层中的脂结一种方式是通过一个糖分子间接同脂双层中的脂结合；合；一种是蛋白质直接与脂双层中的脂结合。一种是蛋白质直接与脂双层中的脂结合。 脂锚定蛋白脂锚定蛋白(Lipid-anchored proteins) Lipid-anchored proteins Lipid-anchored proteinsFunctions of membrane proteinsC. Membran

16、e Carbohydrates2.3 Membrane Carbohydrates 细胞膜上的膜糖都位于细胞膜上的膜糖都位于细胞膜的外表面细胞膜的外表面Outline History of studies on membrane structure Chemical composition of membranes Through the membranes Homeostasis内稳态: the steady state that results from maintaining near constant conditions in the internal environment of

17、a living organism. One of the main structures responsible for maintaining homeostasis is the cell membrane.The cell membrane is semi-permeable半透膜(selectively permeable选择透过性膜); meaning that it allows some molecules to pass through while it prevents others from doing so.1) Diffusion Diffusion扩散: the m

18、ovement of molecules from a region of high concentration高浓度 to an area of low concentration低浓度 This is an example of passive transportation被动运输, meaning that it does not require energy and will occur spontaneously自然地. Oxygen, carbon dioxide and other small molecules are passed in and out of the cell

19、 by this process.2) Osmosis渗透 Osmosis is the diffusion of water. It moves along a concentration gradient顺浓度梯度, sending water from where it is highly concentrated to where it is in low concentration.Terms associated with Osmosis Hypotonic低渗: Something, such as a cell, is hypotonic if there is less so

20、lute dissolved inside it than outside it. The concentration of water inside it therefore higher than the concentration of water outside it. Water will move out of a hypotonic substance which can cause shrinkage.皱缩Terms associated with OsmosisHypertonic 高渗: Something is hypertonic if the concentratio

21、n of solute dissolved inside is more than that outside.The water inside it is therefore lower than the concentration of water outside it. Water will therefore move into a hypotonic substance which can cause an animal cell to burst (plasmolysis原生质分离).Terms associated with Osmosis Isotonic等渗的: Somethi

22、ng is isotonic if the concentration of water inside it is equal to the concentration of water outside it. Water will therefore move into and out of the substance at the same rate.3) Facilitated Diffusion协助扩散 This is diffusion with the help of a protein. Still passive transport.被动运输 Large or charged

23、molecules will either bind to a carrier protein 载体蛋白and diffuse across OR pass through a special integral protein called a channel protein通道蛋白 into or out of the cell.4) Active Transport主动运输 This requires energy to work as it forces substances to go against the concentration gradient逆浓度梯度, from an a

24、rea where they are in low concentration to an area where they are in high concentration.4) Active Transport Active transport uses the main energy source of the cell, ATP, to drive pumps which push substances across the cell membrane against their concentration gradients. Most common pump is the sodium-potassium pump found in nerve cells and