醫(yī)學(xué)細(xì)胞生物學(xué)：Cell Membrane

1、Cell Membrane Model of the cell membrane Membrane structure Specialized structure on cell surfurce cell membrane disease Shiping Ding Associated professor Cell biology Telephone： +86-571-88208023 (office) E-mail： Model of cell membrane 1.A brief history of studies on the structure of the plasmic mem

2、brane A. Conception: Plasma membrane(cell membrane), Intracellular membrane, Biomembrane. B. The history of study Overton(1890s): Lipid nature of PM; J.D.Robertson(1959): The TEM showing:the trilaminar appearance of PM; Unit membrane model; S.J.Singer and G.Nicolson(1972): fluid-mosaic model; K.Simo

3、ns et al(1997): lipid rafts model; Functional rafts in Cell membranes. Nature 387:569-572 2. Singer and Nicolsons Model of membrane structure: The fluid-mosaic model is the “central dogma” of membrane biology. A. The core lipid bilayer exists in a fluid state, capable of dynamic movement. B. Membran

4、e proteins form a mosaic of particles penetrating the lipid to varying degrees. The Fluid Mosaic Model, proposed in 1972 by Singer and Nicolson, had two key features, both implied in its name. Its like a fluid Its like a mosaic Its the Fluid Mosaic Model! fluid mosaic model Cellular membranes have 4

5、 components: phospholipid bilayer transmembrane proteins interior protein network cell surface markers The chemical composition of membranes membrane% protein% lipid% carbohydrate myelin18793 human erythrocyte plasma membrane 49438 mitochondrial inner membrane 79240 amoeba plasma membrane54424 The c

6、omparison of the cell membrane components Membrane Lipids Membrane Lipids: The Fluid Part of the Model Phospholipids: Phosphoglyceride and sphingolipids Glycolipids Sterols ( is only found in animals) vMembrane lipids are amphipathic. vThere are three major classes of lipids. Phospholipid structure

7、consists of -glycerol a 3-carbon polyalcohol acting as a backbone for the phospholipid -2 fatty acids attached to the glycerol -phosphate group attached to the glycerol Phospholipids Figure. Four major phospholipids in mammalian plasma membranes. Note that different head groups are represented by di

8、fferent symbols in this figure and the next. All of the lipid molecules shown are derived from glycerol except for sphingomyelin, which is derived from serine. phosphoglyceride cardiolipin Phosphatidyl inositol sphingolipid glycolipids are membrane components composed of lipids that are covalently b

9、onded to monosaccharides or polysaccharides. glycolipid Figure. Glycolipid molecules. Galactocerebroside (A) is called a neutral glycolipid because the sugar that forms its head group is uncharged. A ganglioside (B) always contains one or more negatively charged sialic acid residues (also called N-a

10、cetylneuraminic acid, or NANA), whose structure is shown in (C). Whereas in bacteria and plants almost all glycolipids are derived from glycerol, as are most phospholipids, in animal cells they are almost always produced from sphingosine, an amino alcohol derived from serine, as is the case for the

11、phospholipid sphingomyelin. Gal = galactose; Glc = glucose, GalNAc = N-acetylgalactos-amine; these three sugars are uncharged. The amount of cholesterol may vary with the type of membrane. Plasma membranes have nearly one cholesterol per phospholipid molecule. Other membranes (like those around bact

12、eria) have no cholesterol. They immobilize the first few hydrocarbon groups of the phospholipid molecules. This makes the lipid bilayer less deformable and decreases its permeability to small water-soluble molecules. Without cholesterol (such as in a bacterium) a cell would need a cell wall. Cholest

13、erol prevents crystallization of hydrocarbons and phase shifts in the membrane. Cholesterol Figure. The structure of cholesterol. Cholesterol is represented by a formula in (A), by a schematic drawing in (B), and as a space-filling model in (C). membranecholesterol phosphotidyl - choline sphingo- my

14、elin phosphotidyl - serine glycolipid s rat liver plasma membrane 3018149- rat liver RER 65533- rat liver nuclear membrane 105533- rat liver myelin 22116712 E coli cytoplasmi c membrane 00- 不同細(xì)胞膜磷脂的組成 micelles; bilayers A liposome is an artificially-prepared vesicle composed of a lipid bilayer. The

15、liposome can be used as a vehicle for administration of nutrients and pharmaceutical drugs. Liposomes can be prepared by disrupting biological membranes (such as by sonication). Liposomes are composed of natural phospholipids, and may also contain mixed lipid chains with surfactant properties. A lip

16、osome design may employ surface ligands for attaching to unhealthy tissue. liposome liposome 脂質(zhì)體的應(yīng)用：脂質(zhì)體的應(yīng)用： 激光共聚焦顯微鏡下觀察激光共聚焦顯微鏡下觀察P(MDS- co-CES)/ Herceptin和納米顆粒的和納米顆粒的 胞內(nèi)分布（時(shí)間點(diǎn)如圖所示）：胞內(nèi)分布（時(shí)間點(diǎn)如圖所示）： （A）在）在HER2高表達(dá)的高表達(dá)的BT474 細(xì)胞中分布細(xì)胞中分布 （B）在）在HER2陰性的陰性的HEK293細(xì)胞中分布細(xì)胞中分布 藍(lán)色：胞核經(jīng)藍(lán)色：胞核經(jīng)DAPI染色染色 紅色：紅色：Alexa Fl

17、uor 647-Herceptin 綠色：載有綠色：載有FITC的的 P(MDS-co-CES) Biomaterials, 30(5): 919-927, 2009, Any Questions? membrane protein Studies Show Proteins In Membrane Membrane Proteins Many Functions Each type of protein in a membrane has a special function Adhesion proteins hold to surface, cells Recognition prote

18、ins recognize “self” Receptor proteins receive messages Enzymes greatly speed-up reactions Transport proteins (active and passive) active require energy to transport passive no energy required for transport Membrane proteins can be associated with the lipid bilayer in different ways Why are proteins

19、 the perfect molecule to build structures in the cell membrane? Classes of amino acids What do these amino acids have in common? nonpolar Triton-X100 Figure. Th e us e of m i l d detergents for solubilizing, purifying, and reconstituting functional membrane protein systems. In this example functiona

20、l Na +-K+ ATPase molecules are purified and incorporated into phospholipid vesicles. The Na+-K+ ATPase is an ion pump that is present in the plasma membrane of most animal cells; it uses the energy of ATP hydrolysis to pump Na+ out of the cell and K+ in, as discussed in Chapter 11. Membrane sample 膜

21、骨架模式圖膜骨架模式圖 Figure. Spectrin molecules from human red blood cells. The protein is shown schematically in (A) and in electron micrographs in (B). Each spectrin heterodimer consists of two antiparallel, loosely intertwined, flexible polypeptide chains called a and b these are attached noncovalently to

22、 each other at multiple points, including both ends. The phosphorylated head end, where two dimers associate to form a tetramer, is on the left. Both the a and b chains are composed largely of repeating domains 106 amino acids long. In (B) the spectrin molecules have been shadowed with platinum. (D.

23、W. Speicher and V.T. Marchesi, Nature 311:177-180; B, D.M. Shotton et al., J. Mol. Biol. 131:303-329) Figure. The spectrin-based cytoskeleton on the cytoplasmic side of the human red blood cell membrane. The structure is shown schematically in (A) and in an electron micrograph in (B). The arrangemen

24、t shown in (A) has been deduced mainly from studies on the interactions of purified proteins in vitro. Spectrin dimers associate head-to-head to form tetramers that are linked together into a netlike meshwork by junctional complexes composed of short actin filaments (containing 13 actin monomers), t

25、ropomyosin, which probably determines the length of the actin filaments, band 4.1, and adducin. The cytoskeleton is linked to the membrane by the indirect binding of spectrin tetramers to some band 3 proteins via ankyrin molecules, as well as by the binding of band 4.1 proteins to both band 3 and gl

26、ycophorin (not shown). The electron micrograph in (B) shows the cytoskeleton on the cytoplasmic side of a red blood cell membrane after fixation and negative staining. (B, courtesy of T. Byers and D. Branton, PNSA. 82:6153-6157) Any Questions? Cell membrane disease 1.1 Hereditary spherocytosis 1.2 c

27、ystic fibrosis Hereditary spherocytosis Hereditary spherocytosis Hereditary spherocytosis Hereditary spherocytosis cystic fibrosis Protein Misfolding Diseases (also known as Protein Conformational Diseases) Disorders arising from the failure of a specific peptide or protein to adopt, or remain in, i

28、ts native structure Diseases in which an impairment in the folding efficiency of a given protein results in a reduction of native folded protein. ribosome nascent chain of CFTR ribosome folded, functional CFTR on the cell membrane end of translation, folding on the ER membrane, translocation to the

29、cell membrane nascent chain of CFTR ribosome nascent chain of CFTR ribosome nascent chain of CFTR misfolded CFTR ribosome nascent chain of CFTR misfolded CFTR no folded CFTR on the cell membrane cystic fibrosis Characteristics of cell membrane Membranes are fluidity vFluidity of membrane lipid. It g

30、ive membranes the ability to fuse, form networks, and separate charge; vMotility of membrane protein. Phospholipids can rapidly diffuse along the plane of the membrane Nearest neighbor replacement rate is 10- 8/sec Flip-flop is a rare process leaflet exchange rate is 6 - 20 h 10-8 sec 6- 20 hours fo

31、r flip-flop Flippases A relatively new discovery! Lipids can be moved from one monolayer to the other by flippase proteins Some flippases operate passively and do not require an energy source Other flippases appear to operate actively and require the energy of hydrolysis of ATP Active flippases can

32、generate membrane asymmetries Van der Waals interactions between fatty acyl chains are the main determinants of acyl chain mobility Below the phase transition temperature fatty acyl chains are in a gel-like (crystalline) state Above the phase transition temperature, fatty acyl chains are in rapid mo

33、tion Membrane Phase Transitions The transition temperature is characteristic of the lipids in the membrane. Double bonds reduce the number of potential van der Walls interactions between fatty acyl chains Cholesterol is an amphipathic steroid that is abundant in plasma membranes Cholesterol can pack

34、 with phospholipids in a 1:1 ratio The “Fluidity” of a Lipid Bilayer Is Determined by Its Composition Short chain fatty acyl groups tend to increase lateral mobility Unsaturated fatty acids tend to increase fluidity Cholesterol and other sterols tend to impede fatty acid mobility (act as a fluidity

35、buffer) Protein fluidity F i g u r e . E x p e r i m e n t demonstrating the mixing 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 plasma membrane, but they intermix with time. The two

36、antibodies used to visualize the proteins can be distinguished in a fluorescence microscope because fluorescein is green whereas rhodamine is red. (Based on observations of L.D. Frye and M. Edidin, J. Cell Sci. 7:319-335) Figure. Antibody-induced patching and capping of a cell-surface protein on a w

37、hite blood cell. The bivalent antibodies cross-link the protein molecules to which they bind. This causes them to cluster into large patches, which are actively swept to the tail end of the cell to form a cap. The centrosome, which governs the head-tail polarity of the cell, is shown in orange. The

38、lateral diffusion of membrane lipids can demonstrated experimentally by a technique called Fluorescence Recovery After Photobleaching (FRAP)（光脫色熒光恢復(fù)技術(shù)光脫色熒光恢復(fù)技術(shù) ）. Figure. Diagram of an epithelial cell showing how a plasma membrane protein is restricted to a particular domain of the membrane. Protein

39、 A (in the apical membrane) and protein B (in the basal and lateral membranes) can diffuse laterally in their own domains but are prevented from entering the other domain, at least partly by the specialized cell junction called a tight junction. Lipid molecules in the outer (noncytoplasmic) monolaye

40、r of the plasma membrane are likewise unable to diffuse between the two domains; lipids in the inner (cytoplasmic) monolayer, however, are able to do so. Figure. Three domains in the plasma membrane of guinea pig sperm defined with monoclonal antibodies. A guinea pig sperm is shown schematically in

41、(A), while each o f t h e t h r e e p a i r s o f micrographs shown in (B), (C), and (D) shows cell-surface immunofluorescence staining with a different monoclonal antibody (on the right) next to a phase-contrast micrograph (on the left) of the same cell. The antibody shown in (B) labels only the anterior head, that in (C) only the posterior head, whereas that in (D) labels only the tail. (Courtesy of Selena Carroll and Diana Myles.) Figure. Four ways in which the lateral mobility of specific plasma membrane proteins can be restricted.