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) 細(xì)胞質(zhì)膜細(xì)胞質(zhì)膜 (Plasma Membrane) 細(xì)胞內(nèi)膜細(xì)胞內(nèi)膜 (Endomembrane ) 細(xì)細(xì)胞胞的的生生物物膜膜體體系系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流動(dòng)鑲嵌模型流動(dòng)鑲嵌模型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 動(dòng)態(tài)結(jié)構(gòu)動(dòng)態(tài)結(jié)構(gòu)in which the components are mobile and capable of coming together to engage in various types of transient or semipermanent interactions. 流動(dòng)鑲嵌模

5、型流動(dòng)鑲嵌模型(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。存在于絕大

6、多數(shù)哺乳動(dòng)物質(zhì)膜和部分內(nèi)膜系統(tǒng)。存在于絕大多數(shù)哺乳動(dòng)物質(zhì)膜和部分內(nèi)膜系統(tǒng)。特征特征：脂筏脂筏與與質(zhì)膜微囊質(zhì)膜微囊（caveolae），又稱，又稱去污劑不溶的富含糖脂區(qū)去污劑不溶的富含糖脂區(qū)（detergent-resistant fraction）.主要含有鞘脂和膽固醇而呈現(xiàn)介于液晶相和凝主要含有鞘脂和膽固醇而呈現(xiàn)介于液晶相和凝膠相之間的膠相之間的液態(tài)有序相液態(tài)有序相（liquid-ordered phase）或或Lo相。以相。以Lo相為特征的脂質(zhì)相為特征的脂質(zhì)微區(qū)四周被流動(dòng)的、液態(tài)無(wú)序相的脂質(zhì)分子包圍，猶如很多小筏漂浮在流動(dòng)的脂微區(qū)四周被流動(dòng)的、液態(tài)無(wú)序相的脂質(zhì)分子包圍，猶如很多小筏漂浮在流

7、動(dòng)的脂質(zhì)海洋中。質(zhì)海洋中。約約70nm70nm左右，是一種動(dòng)態(tài)結(jié)構(gòu)，位于質(zhì)膜的外小頁(yè)。左右，是一種動(dòng)態(tài)結(jié)構(gòu)，位于質(zhì)膜的外小頁(yè)。主要功能：主要功能：信號(hào)轉(zhuǎn)導(dǎo)、膜的運(yùn)送（內(nèi)吞、外排），膽固醇運(yùn)送、維持胞內(nèi)信號(hào)轉(zhuǎn)導(dǎo)、膜的運(yùn)送（內(nèi)吞、外排），膽固醇運(yùn)送、維持胞內(nèi)CaCa2+2+穩(wěn)態(tài)平衡、蛋白分選等。穩(wěn)態(tài)平衡、蛋白分選等。 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固醇類固醇類2. The chemical composition of membranesMembranes contain a wide diversity of lipids, all of which are amphipathic兩親性的兩親性的; that is, they contain both hydrophil

9、ic 親水性親水性and hydrophobic疏水性疏水性 regions. 2.1 Membrane Lipids親水頭部親水頭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 膽固醇；膽固醇； Glycolipids 糖脂糖脂。2.1 Membrane LipidsPhospholipids磷酸磷酸膽堿膽堿甘油甘油磷酸磷酸極性親水頭部極性親水頭部非極性疏水尾部非極性疏水尾

10、部膽固醇膽固醇Movement of Membrane Lipids Liposome脂質(zhì)體脂質(zhì)體 A. Study on nature性質(zhì)研究性質(zhì)研究B. Gene transfer 基因?qū)牖驅(qū)隒. Carrier載體載體 Type Application B. Membrane ProteinsIntegral proteinsPeripheral proteinsLipid-anchored proteins脂錨定蛋白脂錨定蛋白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質(zhì)完成的；生物膜的特定功能主要是由蛋白質(zhì)完成的；膜蛋白約占膜的膜蛋白約占膜的40%40%50%, 50%, 有有5050余種膜蛋白；余種膜蛋白；在不同細(xì)胞中膜蛋白的種類及含量有很大差異。有在不同細(xì)胞中膜蛋白的種類及含量有很大差異。有的含量不到的含量不到25%25%，有的達(dá)到，有的達(dá)到75%75%；一般來(lái)說(shuō)一般來(lái)說(shuō), ,功能越復(fù)雜的膜，其上的蛋白質(zhì)含量越功能越復(fù)雜的膜，其上的蛋白質(zhì)含量越多，種類越多。多，種類越多。整合蛋白整合蛋白(Integral Proteins) 部分或全部鑲嵌部分或全部鑲嵌在細(xì)胞膜中或內(nèi)外兩側(cè)的蛋白質(zhì)；在細(xì)胞膜中或內(nèi)外兩側(cè)的蛋白質(zhì)； 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 ；根據(jù)跨膜次數(shù)將跨膜蛋白分為單次跨膜、多次跨膜、多根據(jù)跨膜次數(shù)將跨膜蛋白分為單次跨膜、多次跨膜、多亞單位跨膜等；跨膜蛋白的跨膜區(qū)為一般為亞單位跨膜等；跨膜蛋白的跨膜區(qū)為一

13、般為螺旋螺旋, , 也也有的是有的是折疊，如孔蛋白；折疊，如孔蛋白；整合蛋白約占膜蛋白的整合蛋白約占膜蛋白的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.外周蛋白為水溶性；外周

14、蛋白為水溶性；占膜蛋白總量的占膜蛋白總量的20%20%30%30%，在紅細(xì)胞中占，在紅細(xì)胞中占50%50%，如紅，如紅細(xì)胞的血影蛋白和錨定蛋白都是外周蛋白。細(xì)胞的血影蛋白和錨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;又稱脂連接蛋白又稱脂連接蛋白(lipid-linked proteins)，同脂的結(jié)同脂的結(jié)合有兩種方式：合有兩種方式：一種方式是通過(guò)一個(gè)糖分子間接同脂雙層中的脂結(jié)一種方式是通過(guò)一個(gè)糖分子間接同脂雙層中的脂結(jié)合；合；一種是蛋白質(zhì)直接與脂雙層中的脂結(jié)合。一種是蛋白質(zhì)直接與脂雙層中的脂結(jié)合。 脂錨定蛋白脂錨定蛋白(Lipid-anchored proteins) Lipid-anchored proteins Lipid-anchored proteinsFunctions of membrane proteinsC. Membran

16、e Carbohydrates2.3 Membrane Carbohydrates 細(xì)胞膜上的膜糖都位于細(xì)胞膜上的膜糖都位于細(xì)胞膜的外表面細(xì)胞膜的外表面Outline History of studies on membrane structure Chemical composition of membranes Through the membranes Homeostasis內(nèi)穩(wěn)態(tài): 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選擇透過(guò)性膜); meaning that it allows some molecules to pass through while it prevents others from doing so.1) Diffusion Diffusion擴(kuò)散: the m

18、ovement of molecules from a region of high concentration高濃度 to an area of low concentration低濃度 This is an example of passive transportation被動(dòng)運(yùn)輸, 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滲透 Osmosis is the diffusion of water. It moves along a concentration gradient順濃度梯度, sending water from where it is highly concentrated to where it is in low concentration.Terms associated with Osmosis Hypotonic低滲: 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.皺縮Terms associated with OsmosisHypertonic 高滲: 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原生質(zhì)分離).Terms associated with Osmosis Isotonic等滲的: 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協(xié)助擴(kuò)散 This is diffusion with the help of a protein. Still passive transport.被動(dòng)運(yùn)輸 Large or charged

23、molecules will either bind to a carrier protein 載體蛋白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主動(dòng)運(yùn)輸 This requires energy to work as it forces substances to go against the concentration gradient逆濃度梯度, 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