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New Words,Lipids, Phospholipids , Glycolipids , Cholesterols,脂类, 磷脂 , 糖脂 , 胆固醇,lipid bilayer, molecule , amphipathic, asymmetry,fluidity,脂双层, 分子 , 双亲性 , 不对称性 , 流动性,Chapter 3: The Plasma Membrane,I. THE CHEMICAL COMPOSITION AND STRUCTURE OF MEMBRANE (化学组成及分子结构)II. MEMBRANE TRANSPORT OF SUBSTANCES (物质运输)III. THE CELL SURFACE (细胞表面),nuclear envelope,endoplasmic reticulum,mitochondrion,lysosome,plasmicmembrane,Golgi complex,An Overview of membrane functions,1. Define the boundaries of the cell and its organelles. 2. Serve as loci for specific functions. 3. provide for and regulate transport processes. 4. contain the receptors needed to detect external signals. 5. provide mechanisms for cell-to-cell contact, communication and adhesion,I. THE CHEMICAL COMPOSITION AND STRUCTURE OF MEMBRANE,Learning objectives:The Chemical Composition of Membranes化学组成2. The Character of Biological Membrane 生物膜特性3. Model of membrane structure-结构模型,脂类蛋白质糖类,磷脂糖脂胆固醇,整合蛋白外周蛋白,糖蛋白糖脂,细胞膜的成分,水、无机盐、金属离子,1. The chemical composition of membranes,1.1 Membrane Lipids:膜脂,Phospholipids:磷脂 Phosphoglyceride and sphingolipids Glycolipids糖脂 Cholesterols ( is only found in animals)胆固醇,There are three major classes of lipids:,Figure 3-1. The parts of a phospholipid molecule. Phosphatidyl choline, represented schematically (A), in formula (B), as a space-filling model (C), and as a symbol (D). The kink due to the cis-double bond is exaggerated in these drawings for emphasis.,Figure 3-2. 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-acetylneuraminic 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 phospholipid sphingomyelin. Gal = galactose; Glc = glucose, GalNAc = N-acetylgalactos-amine; these three sugars are uncharged.,Figure 3-3. 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).,Figure 3-4. Cholesterol in a lipid bilayer. Schematic drawing of a cholesterol molecule interacting with two phospholipid molecules in one leaflet of a lipid bilayer.,Figure 3-5. A lipid micelle and a lipid bilayer seen in cross-section. Lipid molecules form such structures spontaneously in water. The shape of the lipid molecule determines which of these structures is formed. Wedge-shaped lipid molecules (above) form micelles, whereas cylinder-shaped phospholipid molecules (below) form bilayers.,Membrane lipids are amphipathic,亲水端,疏水端,双亲性分子在水中的结构形式,水,存在的方式,内在膜蛋白/整合膜蛋白外在膜蛋白/外周蛋白脂锚定蛋白,二、膜蛋白,细胞膜的功能的主要体现者。,Figure 3-7. Six ways in which membrane proteins associate with the lipid bilayer.,Peripheral proteins外周蛋白,Integral proteins整合蛋白,1.2 Membrane Proteins:膜蛋白,Figure 3-8. Simplified diagram of the cell coat (glycocalyx). The cell coat is made up of the oligosaccharide side chains of glycolipids and integral membrane glycoproteins and the polysaccharide chains on integral membrane proteoglycans. In addition, adsorbed glycoproteins and adsorbed proteoglycans (not shown) contribute to the glycocalyx in many cells. Note that all of the carbohydrate is on the noncytoplasmic surface of the membrane.,cell coat,1.3 Membrane carbohydrates:膜糖,三、膜糖类,糖类与脂质和膜蛋白以共价键方式结合,在真核细胞表面形成一层很厚的包被,这层由糖分子侧链在细胞表面形成的结构叫细胞外被,又叫糖萼。,类型:糖蛋白=糖+膜蛋白糖脂=糖+脂质,功能:保护、润滑、识别、黏附,发炎,2. The Character of Biological membrane,2.1 Membrane asymmetry-不对称性,2.2 Membrane fluidity-流动性,The asymmetry of membrane lipids, proteins, carbohydrate,The fluidity of membrane lipids and proteins,EF,PF,小鼠肝细胞膜,一、膜的不对称性,10-6s,105s,10-9 s,Fluidity of membrane lipid. It give membranes the ability to fuse, form networks, and separate charge;,侧向扩散10-7s,翻转运动(少见)105s,旋转运动,磷脂分子运动的几种方式,弯曲运动10-9 s,二、膜的流动性,Motility of membrane protein.,The lateral diffusion of membrane lipids can demonstrated experimentally by a technique called Fluorescence Recovery After Photobleaching (FRAP).,Figure 3-9. Experiment 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 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),3. A brief history of studies on the structrure of the plasmic membrane,A. Conception: Plasma membrane(cell membrane), Intracellular membrane, Biomembrane.B. The history of studyOverton(1890s): Lipid nature of PM;, J.D.Robertson(1959): The TEM showing:the trilaminar appearance of PM; Unit membrane model;(单位膜模型) S.J.Singer and G.Nicolson(1972): fluid-mosaic model;(流动镶嵌模型) K.Simons et al(1997): lipid rafts model;(脂筏模型) Functional rafts in Cell membranes. Nature 387:569-572,流动镶嵌模型的特点,膜脂是由双层脂质分子构成脂质双层是流动的,脂质和蛋白质分子都可以流动蛋白质嵌入细胞膜的方式包括:,膜外在蛋白/脂锚定蛋白,膜内在蛋白,膜蛋白,Passive transport-被动运输Active transport-主动运输Membrane Vesicle Transport-囊泡运输Endocytosis-胞吞作用Exocytosis-胞吐作用Free diffusion-自由扩散Facilitated diffusion-易化扩散Ionic pump-离子泵Co-transport-协同运输,. MEMBRANE TRANSPORT OF SUBSTANCES,Travers Membrane Transport-穿膜运输 1.1 Passive transport-被动运输 1.2 Active transport-主动运输2. Membrane Vesicle Transport-膜泡运输 2.1 Endocytosis-胞吞作用 2.2 Exoocytosis-胞吐作用,Travers Membrane Transport-穿膜运输,1.1 Passive transport-被动运输Free diffusion-自由扩散Facilitated diffusion-易化扩散1.2 Active transport-主动运输 Ionic pump-离子泵 Co-transport-协同运输,Symport-同向运输Antiport-对向运输,1.1.1 Free diffusion自由扩散,It doesnt need the help of membrane proteinIt doesnt consume ATPSubstane moves from a region of high concentration to a region of low concertration,Feature:,弱极性小分子(乙醇),气体小分子,极性小分子(水、尿素、甘油),非极性大分子(葡萄糖),离子,极性大分子,人工脂膜简单扩散实验,1.1.2 Facilitated diffusion易化扩散,It needs the help of transport proteinIt doesnt consume ATPSubstanse moves from a region of high concentration to a region of low concertration,Feature:,转运蛋白类型:载体蛋白(单糖、氨基酸等) 易化扩散或主动运输通道蛋白(离子)易化扩散,Most of the channel proteins are ion channels, including three types, with ion channels that they can be opened and closed,Carrier proteins bind one or more solute molecules on one side of the membrane and then undergo a conformational change that transfer the solute to the other side of the membrane.,葡萄糖的转运载体蛋白,易化扩散,构成:实际上就是Na+

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