分子细胞生物学：10cell membrane

1、细胞膜（质膜）细胞膜（质膜）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（细胞膜）plasma membrane (质膜)Biological membrane(生物膜): plasma membrane（质膜） internal membrane（细胞内膜 ） 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，Found: the more fat-soluble, the easier to be absorbed.The membrane is composed of lipids ？1925，red blood cell extract，Found: 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 -著名的与膜表面糖蛋白有关的疾病著名的与膜表面糖蛋白有关的疾病（羊scrapie,牛mad cow disease,人ku

14、ru, Creutzfeldt-Jacob disease）致病原因：致病原因：PrP变成PrP*PrP： 质膜表面糖蛋白，神经细胞含量特别丰富，功能不明， 正常情况下偶可改变构象成为PrP* 。PrP*：正常PrP二维和三维结构改变，折叠错误。 两个特点： 1，形成交联原纤维，抵抗蛋白酶水解，易于聚集。 2，能使与其接触的PrP也变成PrP*，从而具有感染性。引起疯牛病的引起疯牛病的异常异常PrP*蛋白蛋白正常正常PrP蛋白蛋白异常异常PrP*有有传染性，传染性，使其它正常使其它正常PrP变成异常变成异常PrP*正常情况下正常情况下偶然发生偶然发生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 ( (一条寡糖链一条寡糖链, ,常有分支常有分支, ,糖含量低糖含量低) ) glycoproteins- multiple branched oligosaccharides + protein ( (多条寡糖链多条寡糖链, ,常有分支常有分支, ,糖含量低糖含量低) ) proteoglycan-multiple non-branched long polysaccharides + protein ( (多条聚糖链

18、多条聚糖链, ,无分支无分支, ,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综合思考题1. 你的一个朋友遭了蛇咬，差一点死于广泛溶血。幸好他当时抓住了毒蛇，他知道你是学生物医学的，要你帮助分析毒蛇的毒汁为什么会造成溶血(红细胞膜破裂)。你发现毒汁含有3种成分：蛋白酶、神经酰胺酶和磷脂酶。用这3种成分分别处理纯化的红细胞，发现只有磷脂酶造成溶血，进一步分析溶血产物，发现有大量游离的磷酰基胆碱（带磷酸基团的胆碱）和二酰基甘油（带两条脂肪酸链的甘油）。请回答（1）这种磷脂酶的作用对象是什么磷脂分子？在分子的那个部位

21、发生切割作用？（2）为什么是磷脂酶而不是蛋白酶和神经酰胺酶造成溶血？（注：蛋白酶可打开蛋白质的肽键，神经酰胺酶可去除神经节苷脂上的唾液酸，磷脂酶可切割磷脂中的键。） 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