分子細胞生物學：10cell membrane

1、細胞膜（質(zhì)膜）細胞膜（質(zhì)膜）Cell membraneunder light microscope：The boundary membrane(separating & communicating)？Think：The features the boundary membrane requiresDramatic differences in chemical composition inside and outside the cell.Substance transportInformation exchangeseparation and communicationThe fun

2、ctions of cell membrane?An electron micrograph of a plasma membrane of a human red blood cell- two dark sheets sandwich one bright sheet, 7 nm in width cell membrane（細胞膜）plasma membrane (質(zhì)膜)Biological membrane(生物膜): plasma membrane（質(zhì)膜） internal membrane（細胞內(nèi)膜 ） common structure and similar functions

3、plasma membrane 3 componentsUnique physicochemical natures and sophisticated interaction1. Membrane lipids2. Membrane proteins 3. Membrane glycoconjugatesNerve myelin： lipid 75Mito membrane： protein 75general： lipid 50 protein 4050、 sugar 110Myelin of the sciatic nerve Inner membrane of the mitochon

4、drionHistory of discovery1890 ，Overton：root absorption，F(xiàn)ound: the more fat-soluble, the easier to be absorbed.The membrane is composed of lipids ？1925，red blood cell extract，F(xiàn)ound: the coverage area of lipid molecules is twice as the area of red cell membrane. Lipid bilayer on the membrane？19201930，

5、Found: not only lipids!1935，H.Davson & J.Danielli proposed the model for membrane structure，1950 proposed a revision.the membrane structure is a bilayer with proteins bound to the two sides.fluid mosaic model -proposed by Singer & Nicolson in 19701. The lipids are arranged in two closely app

6、osed sheets, forming a lipid bilayer2. The proteins mosaic in or associated to the lipid bilayer3. The two sides of the membrane is asymmetric4. Both the membrane lipid and membrane proteins are of fluidityFluid mosaic modelAn updated version：glyco-conjugates3. fluidity1. Type and molecular structur

7、e2. arrangement4. asymmetry(2) cholesterol (2) cholesterol (3) glycolipids(3) glycolipids(1) phospholipids(1) phospholipidsAll are amphipathic- both hydrophilic (water-loving) and hydrophobic (water-fearing)1. Type and molecular structureFigure 11-5 Essential Cell Biology ( Garland Science 2010)Figu

8、re 11-7 Essential Cell Biology ( Garland Science 2010)Phosphatidycholine(phospholipid)Polar head（hydrophilic）nonpolar tails（hydrophobic）Figure 11-10 Essential Cell Biology ( Garland Science 2010)Fat molecules are hydrophobic, whereas phospholipids are amphipathic2. Arrangement of lipid moleculesLipi

9、d bilayer on the membrane(1) Lateral diffusion(2) rotation(3) flexion(4) flip-flop3. 3. fluidity(1) Phospholipids differ in two halves of bilayer(2) Glycolipids are in the external monolayer of the plasma membrane4. 4. asymmetry of lipid bilayerPhospholipids with amino acid headsGlycolipids and phos

10、pholipids with cholin heads2. The structures of membrane proteins1. The ways membrane proteins associate with the lipid bilayer3. The structures versus the functions4. The mobility of membrane proteins1 2 3 4 5 6 7 The ways membrane proteins associate with the lipid bilayerAsymmetry of membrane prot

11、eins on the bilayerl Sugars are added at the external surfaces of the bilayerl The cysteines are in the different forms at two sides -free thiols in the cytoplasmic side (-SH) - disulfide bonds in the non-cytoplasmic side (S-S)2. barrel sheet rolls into a barrel1. helixAlso amphipathic Hydrophobic a

12、.ahydrophobic segments hydrophobic areasHydrophilic a.ahydrophilic segments hydrophilic areas2. The structures of membrane proteinsFigure 11-28 Essential Cell Biology ( Garland Science 2010)1. helixFigure 11-25 Essential Cell Biology ( Garland Science 2010)2. barrelFigure 11-23 Essential Cell Biolog

13、y ( Garland Science 2010)A segment of helix crossing a bilayerA transmembrane hydrophilic pore can be formed by multiple helixFigure 11-25 Essential Cell Biology ( Garland Science 2010)3. The structures versus the functions Prion diseases -著名的與膜表面糖蛋白有關的疾病著名的與膜表面糖蛋白有關的疾病（羊scrapie,牛mad cow disease,人ku

14、ru, Creutzfeldt-Jacob disease）致病原因：致病原因：PrP變成PrP*PrP： 質(zhì)膜表面糖蛋白，神經(jīng)細胞含量特別豐富，功能不明， 正常情況下偶可改變構象成為PrP* 。PrP*：正常PrP二維和三維結(jié)構改變，折疊錯誤。 兩個特點： 1，形成交聯(lián)原纖維，抵抗蛋白酶水解，易于聚集。 2，能使與其接觸的PrP也變成PrP*，從而具有感染性。引起瘋牛病的引起瘋牛病的異常異常PrP*蛋白蛋白正常正常PrP蛋白蛋白異常異常PrP*有有傳染性，傳染性，使其它正常使其它正常PrP變成異常變成異常PrP*正常情況下正常情況下偶然發(fā)生偶然發(fā)生The Nobel Prize in Phy

15、siology or Medicine 1997 The Nobel Prize in Physiology or Medicine 1997for his discovery of Prions - a new biological principle of infection Stanley B. Prusiner USA University of California School of Medicine San Francisco, CA, USA b. 1942(1) Membrane proteins are mobile and diffusible, but do not f

16、lip-flop hybrid cell hybrid cell (2) The mobility is restricted intestine epithelial cells intestine epithelial cells 到4. The mobility of membrane proteinsFigure 11-32 Essential Cell Biology ( Garland Science 2010)Figure 11-34 Essential Cell Biology ( Garland Science 2010)1. The ways glyco-conjugate

17、s associate to bilayer2. The functions glycolipids- a branched oligosaccharides + lipid ( (一條寡糖鏈一條寡糖鏈, ,常有分支常有分支, ,糖含量低糖含量低) ) glycoproteins- multiple branched oligosaccharides + protein ( (多條寡糖鏈多條寡糖鏈, ,常有分支常有分支, ,糖含量低糖含量低) ) proteoglycan-multiple non-branched long polysaccharides + protein ( (多條聚糖鏈

18、多條聚糖鏈, ,無分支無分支, ,糖含量高糖含量高) )Figure 11-35 Essential Cell Biology ( Garland Science 2010)Functionsl cell coat - protectionl membrane glycoproteins - recognition ABO blood type ABO blood typeABO blood typesDifference liesBlood type antigens and their receptors are transmembrane glycoproteins a selectiv

19、e barrier & a communicating mediatorThe functions of the plasma membrane? 1. transport（plasma membrane & internal membraanes） 2. cell recognition and adhesion 3. cell signaling 4. cell junctions and tissue constructionsbarrierimpermeable poresselectively permeable separating- extracellular s

20、ignals communicating- signaling, recognition, cell junctions transportinformation綜合思考題1. 你的一個朋友遭了蛇咬，差一點死于廣泛溶血。幸好他當時抓住了毒蛇，他知道你是學生物醫(yī)學的，要你幫助分析毒蛇的毒汁為什么會造成溶血(紅細胞膜破裂)。你發(fā)現(xiàn)毒汁含有3種成分：蛋白酶、神經(jīng)酰胺酶和磷脂酶。用這3種成分分別處理純化的紅細胞，發(fā)現(xiàn)只有磷脂酶造成溶血，進一步分析溶血產(chǎn)物，發(fā)現(xiàn)有大量游離的磷酰基膽堿（帶磷酸基團的膽堿）和二?；视停◣蓷l脂肪酸鏈的甘油）。請回答（1）這種磷脂酶的作用對象是什么磷脂分子？在分子的那個部位

21、發(fā)生切割作用？（2）為什么是磷脂酶而不是蛋白酶和神經(jīng)酰胺酶造成溶血？（注：蛋白酶可打開蛋白質(zhì)的肽鍵，神經(jīng)酰胺酶可去除神經(jīng)節(jié)苷脂上的唾液酸，磷脂酶可切割磷脂中的鍵。） 1. transport（plasma membrane & internal membraanes） 2. cell recognition and adhesion 3. cell signaling 4. cell junctions and tissue constructionsMembrane transport proteins：For small molecule transportFigure 1-25 Essential Cell Biology ( Garland Science 201