1、細(xì)胞生物學(xué)第四章細(xì)胞質(zhì)膜與細(xì)胞表面MEMBRANE STRUCTURE AND FUNCTION Biological membranes surround a cell and separate cellular compartments. A membrane is a mosaic of lipids, proteins, and carbohydrates. One of the key functions of a membrane is selective permeability: the ability to allow some substances through but

2、not others. This ability of a biological membrane to control the passage of substances is fundamental to life.Puncture a cell with a fine needle, and cytoplasm will not ooze out. Instead, the cell surface will appear to flow over the puncture and seal it. The membrane behaves as if it were fluid. Th

3、is fluidity results from the properties of phospholipids, the most abundant components in cell membranes. When placed in fluid, phospholipids cluster together to form what is called a lipid bilayer. The lipid bilayer is the structural basis of all cell membranes. A cell is separated from its environ

4、ment by a selectively permeable plasma membrane. The plasma membrane is commonly described as a fluid mosaic. It is like a mosaic in having diverse protein molecules embedded in a matrix of phospholipids. Its component proteins and phospholipid molecules can move about, so it is quite fluid and flex

5、ible. The phospholipids in a membrane form a two-layer framework called a phospholipid bilayer. The steroid cholesterol helps stabilize the phospholipids. Carbohydrate molecules are attached to some of the molecules that make up the membrane. (教材教材P337）.unzippedProteinrw32b2a.exe類脂分子自我組裝成脂質(zhì)體類脂分子自我組裝

6、成脂質(zhì)體 The graphic on the following page shows the structure of one of the most common phospholipids in animal cell membranes. surface-to-volume ratio A mathematical relationship in which volume increases with the cube of the diameter, but surface area increases only with the square. 第一節(jié) 細(xì)胞質(zhì)膜plasma me

7、mbrane 一 細(xì)胞膜的結(jié)構(gòu)模型教材（P64）1 三夾板 2 單位 3 流動(dòng)鑲嵌4 目前對質(zhì)膜的認(rèn)識（原版P255）plasma membrane Of cells, the outermost membrane, the boundary between the cytoplasm and the fluid bathing the cell. Its lipid bilayer is the basic structural part of the membrane; diverse proteins embedded in the bilayer or attached to its

8、surfaces carry out most functions, such as transport and reception of extracellular signals. The proteins embedded in a lipid bilayer or attached to one of its surfaces carry out most membrane functions. Many are enzyme components of metabolic machinery. Others are transport proteins, receptor prote

9、ins, recognition proteins, or adhesion proteins. The graphic below describes the function of these various membrane proteins. Phosphatidycholine, a phospholipid found in animal cell membranes.The molecule has a hydrophilic (water-loving) head and hydrophobic (water-dreading) fatty acid tails. Move y

10、our cursor over the molecule to identify these regions. 2膜脂（一）成分（1）磷脂 （ phospholipid） 卵磷脂 （Phosphatidycholine）（2）糖脂 （ glycolipids） A 紅細(xì)胞表面的ABO血型糖脂（教材P65）B 神經(jīng)節(jié)苷脂（gangliosides） 變化最多、最復(fù)雜的一類 glycolipids 是神經(jīng)細(xì)胞的特征成分。兒童遺傳性致死疾病- Tay-Sachs 病細(xì)胞中缺乏氨基己糖苷酶氨基己糖苷酶（己糖胺酶A） 不能把神經(jīng)節(jié)苷脂（gangliosides） Gm2轉(zhuǎn)化為神經(jīng)節(jié)苷脂（ganglios

11、ides） Gm3，結(jié)果Gm2在腦細(xì)胞中積累，導(dǎo)致中樞神經(jīng)系統(tǒng)退化，直至死亡。（3）膽固醇（二）膜脂的運(yùn)動(dòng)方式（原版P259）（三）脂質(zhì)體Liposomes （原版258）phospholipid micelle spherical liposome artificial lipid bilayer, called a black membrane三 膜蛋白血影（原267）（一）類型（二）結(jié)合方式（原270 271）（三）去垢劑（原P266）四 膜的流動(dòng)性（一）膜脂的流動(dòng)性（二）膜蛋白的流動(dòng)性（原P276-281）The experiment demonstrating the mixing

12、of plasma membrane proteins on mouse-human hybrid cells. The mouse and human proteins are initially confined to their own halves of the newly formed heterocaryon異核體 plasma membrane, but intermix with time.Antibody-induced patching (clustering) of antigens on the surface of a lymphocyte. Whereas mono

13、valent antibodies remain diffusely distributed on the lymphocyte surface, bivalent antibodies cross-link the antigens and cluster them into patches.Electron micrographs showing diffuse distribution of ferritin(鐵蛋白)-coupled monovalent antibodies (A) and clustering of ferritin-coupled bivalent antibod

14、ies (B) on the surface of a lymphocyte. Each ferritin molecule appears as a black dot. (Courtesy of Durward Lawson.)Antibody-induced patches are rapidly swept to the tail of the lymphocyte, where they form a “cap”. Often the antibodies (and the proteins to which they bind) are then ingested into end

15、ocytotic vesicles and the lymphocyte adopts a shape that is characteristic of locomotion.Immunofluorescence micrographs showing diffuse, patchy, and capped distributions of fluorescent antibodies on lymphocytes. Monovalent antibodies show diffuse staining (A), while bivalent antibodies initially clu

16、ster into patches (B) and then cap (C). (Courtesy of Stefanello dePetris.)五 膜的不對稱性 分析方法 freeze-fracture electron microscopy After the fracturing process shown here, the exposed fracture faces are shadowed with platinum and carbon, the organic material is digested away, and the resulting platinum rep

17、lica is examined in the electron microscope.（原272 273）（一） 膜脂的不對稱性（教材70-71）（二）膜蛋白的不對稱性細(xì)胞表面的特化結(jié)構(gòu)一 膜骨架（一）紅細(xì)胞的生物學(xué)特征（二）紅細(xì)胞質(zhì)膜蛋白和膜骨架紅細(xì)胞膜蛋主要包括 1 血影蛋白spectrin2 錨蛋白ankyrin. 3 帶三蛋白 band III proteins 4 肌動(dòng)蛋白actin 4血型糖蛋白 glycophorin （原270 271 274） （原269） The two spectrin polypeptide chains are aligned in parallel

18、 and are variably coiled around each other to form flexible dimers (see Figure 6-23). The spectrin dimers join head to head to form tetramers that are linked together into a network by short actin filaments and other proteins on the cytoplasmic surface of the membrane. Spectrin molecules also intera

19、ct indirectly with band III proteins via another protein called ankyrin. ABO血型抗原物質(zhì)在那mobijiao二 鞭毛和纖毛（一）鞭毛和纖毛的結(jié)構(gòu)（教材254）（二） 不運(yùn)動(dòng)纖毛綜合癥第二節(jié) 細(xì)胞連接我們要得到分離的細(xì)胞，往往要對動(dòng)物、植物體中的組織進(jìn)行處理，這說明構(gòu)成組織的細(xì)胞之間有機(jī)械的連接。哺乳動(dòng)物胚胎在血液循環(huán)系統(tǒng)發(fā)育之前，細(xì)胞之間有營養(yǎng)和水分的聯(lián)系。細(xì)胞間營養(yǎng)分配暢通，說明細(xì)胞間也有生理活動(dòng)的聯(lián)系。我們統(tǒng)稱這些聯(lián)系類型為細(xì)胞連接。細(xì)胞連接是多細(xì)胞有機(jī)體中相鄰細(xì)胞相互聯(lián)系、協(xié)同作用必不可少的組織形式。它是對細(xì)胞功

20、能的一種補(bǔ)充。l 按其功能可以將細(xì)胞連接分成兩大類，一類是機(jī)械連接，另一類是通訊連接（ ）。 細(xì)胞連接的分類1 機(jī)械連接-故名思意，這種連接主要起到把細(xì)胞和細(xì)胞機(jī)械連系在一起的作用。（1） 緊密連接（ ）緊密連接是脈體上皮細(xì)胞特有的連接方式。它存在于細(xì)胞頂部下方質(zhì)膜上的一個(gè)特化區(qū)域。（圖）目前認(rèn)為緊密連接的構(gòu)造是這樣的，相鄰質(zhì)膜上的許多跨膜蛋白互相之間在對應(yīng)的位置上互相連接。這樣就構(gòu)成 了一條封閉索（ ）。緊密連接正是由數(shù)條交錯(cuò)成網(wǎng)的封閉索組成（圖） 緊密連接普遍存在于脊椎動(dòng)物體內(nèi)各種腔道的上皮細(xì)胞中，除了具有機(jī)械的支持功能外還有一個(gè)重要的功能，它封閉了細(xì)胞之間還有一個(gè)重要的功能，它封閉了細(xì)胞

21、之間的空隙，將細(xì)胞連接成具有的空隙，將細(xì)胞連接成具有 韌性的一層，韌性的一層，使這一細(xì)胞層內(nèi)側(cè)的大多數(shù)物質(zhì)不能自由使這一細(xì)胞層內(nèi)側(cè)的大多數(shù)物質(zhì)不能自由通透。通透。如， ，腸腔內(nèi)容物不能沿腸上皮細(xì)胞側(cè)壁溢入體液中。腸上皮細(xì)胞對多糖 基酸重營 物質(zhì)的吸收的靠分布在細(xì)胞頂部質(zhì)膜上的主動(dòng)運(yùn)輸載體完成的，而交多糖營養(yǎng)物質(zhì)從細(xì)胞內(nèi)運(yùn)輸?shù)郊?xì)胞外液是靠位于細(xì)胞基部和側(cè)面質(zhì)膜 上被動(dòng)運(yùn)輸載體完成的。顯然，這一系列運(yùn)輸過程的正常有序運(yùn)行有賴于不同功能的載體蛋白在質(zhì)膜上的不同分布，正是緊密連接封閉了細(xì)胞間隙維持了這兩種載體蛋白的正常分布，從面保證了小腸上皮細(xì)胞的極性的吸收功能。Schematic drawing o

22、f a tight junction between epithelial cells of the small intestine. The adjacent plasma membranes are held together by continuous strands of junctional proteins that make contact across the intercellular chemical synapse At a gap junction, small molecules pass directly from the cytoplasm of one cell

23、 to the cytoplasm of the other. At a chemical synapse, the presynaptic nerve cell secretes a chemical signal (neurotransmitter) that diffuses across the synaptic cleft and signals the postsynaptic cell at its surface. (2) 錨定連接錨定連接（ ） 細(xì)胞能夠結(jié)成一個(gè)有一定機(jī)械支撐能力，一個(gè)有利于發(fā)揮具功能的有序的細(xì)胞群體主要是靠 錨定連接。錨定連接是一個(gè)細(xì)胞 中的骨架系統(tǒng)成分與另

24、一個(gè)細(xì)胞 中的骨架成分相連接 （橋粒、粘合帶）；以及一個(gè)細(xì)胞 的骨架系統(tǒng)和細(xì)胞外基質(zhì)相連接（半橋粒、粘合斑）構(gòu)成的。錨定連接又可分為與中間纖維相關(guān)的連接（橋粒、半橋粒）和與肌動(dòng)蛋白相關(guān)的連接（粘合帶、粘合斑）。 粘合帶 連接細(xì)胞與細(xì)胞 粘合斑 連接細(xì)胞與細(xì)胞 橋粒 連接細(xì)胞與細(xì)胞 半橋粒 連接細(xì)胞與細(xì)胞外基質(zhì)橋粒（）和半橋粒（）有一種天皰瘡患者，他的體液滲漏至上皮導(dǎo)致嚴(yán)重的表皮大皰，這是由于患者的身體產(chǎn)生了某種橋粒連接蛋白的抗體，這些抗體作用于皮膚上皮細(xì)胞的橋粒使其失去功能的緣故。可見橋粒對維持上皮結(jié)構(gòu)的正常是非常重要的。橋粒在細(xì)胞之間的連接作用如同鉚釘，它的結(jié)構(gòu)也呈鉚構(gòu)樣半橋粒在形態(tài)上類似于

25、半個(gè)橋粒，它位于上皮細(xì)胞的底面。作用是使上皮細(xì)胞固著在基底膜，也稱基板（ ）上，在半橋粒中，細(xì)胞質(zhì)的中間纖維 不是 過而是附著在半橋粒的致密斑內(nèi)（圖） 粘合帶（ ）與粘合斑（ ） 在上皮細(xì)胞緊密連接的下方常有由相鄰細(xì)胞質(zhì)膜相互粘合形成的一條連接的帶，稱粘合帶。此處相鄰細(xì)胞質(zhì)膜的粘著作用要靠細(xì)胞粘合素（）它是一種衣附于離子的跨膜連接糖蛋白，從結(jié)構(gòu)上 ，與粘合帶相連的纖維不是中間纖維而是肌動(dòng)蛋白纖維。粘合斑則是細(xì)胞中肌動(dòng)蛋白絲與細(xì)胞外基質(zhì)相連形成的，是以點(diǎn)狀接觸（）的形式完成。所以稱粘合斑。三、通訊連接 （1） 間隙連接（2） 化學(xué)突觸（3） 胞間連絲細(xì)胞結(jié)合成組織就是要發(fā)揮細(xì)胞在各方面的群體效應(yīng)

26、，這在有賴于細(xì)胞組織內(nèi)部一個(gè)代謝和行為上互相協(xié)作、協(xié)調(diào)一致的機(jī)制。這一機(jī)制是靠細(xì)胞之間的通訊連接方式間隙連接來實(shí)現(xiàn)的。（1） 間隙連接、間隙連接的結(jié)構(gòu) 間隙連接的結(jié)構(gòu)和機(jī)械連接的構(gòu)造不相同，它雖然也有機(jī)械連接的作用但它的構(gòu)造主要是細(xì)胞間生理偶聯(lián)的需求。間隙連接是適應(yīng)和滿足由連接子（）的形式構(gòu)成。 每個(gè)連接子都是一個(gè)跨膜蛋白顆粒，由6個(gè)相同的亞單位環(huán)繞排列組成的中間結(jié)構(gòu)，直徑為67納米。組成連接子的亞單位稱連接蛋白（）呈棒狀結(jié)構(gòu)。六個(gè)棒狀結(jié)構(gòu)的連接蛋白排列成連接子時(shí)有一定的傾斜，傾斜的角度可受a離子的濃度影響。這種構(gòu)型的變化可能是連接子通道受調(diào)控啟閉的基礎(chǔ)。當(dāng)相鄰細(xì)胞質(zhì)膜上的二個(gè)連接子互相吻合時(shí)

27、，就在兩個(gè)細(xì)胞之間形成一條直徑為1.5的水通道。連接子在質(zhì)膜 上經(jīng)常成 出現(xiàn)其區(qū)域大小不一。有的區(qū)域會有幾對，有的甚至?xí)谐?上萬對連接子。 、間隙連接的功能 把因缺乏胸苷激酶的突變細(xì)胞（不能合成）與正常細(xì)胞一同時(shí)，發(fā)現(xiàn)凡是與正常細(xì)胞之間互通間隙連接的突變細(xì)胞都自己合成。放射性實(shí)驗(yàn)表明，是正常細(xì)胞合成的三磷酸胸苷通過間隙連接進(jìn)入了突變細(xì)胞，參與了的合成。協(xié)調(diào)細(xì)胞群體的生物學(xué)功能協(xié)調(diào)細(xì)胞群體的生物學(xué)功能.當(dāng)胰腺細(xì)胞受體接受激素后，第二信使和a離子濃度增高，促使胰腺細(xì)胞中的分泌泡向外釋放蛋白酶消化液.這些第二信使可以通過間隙連接進(jìn)入其相鄰的細(xì)胞。因此只要有部分細(xì)胞接受激素，作用就會有更多的脈泡細(xì)胞同時(shí)向外分泌消化液。間隙