微生物学史微生物学史 (6).ppt

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1、Bacterial Plasma MembranesAfter learning this section,you should be able to:Describe the fluid mosaic model of membrane structure and identify the types of lipids typically found in bacterial membranes Cell envelopeFunctions of Plasma Membranes1.A primary role of all plasma membranes is that they ar

2、e selectively permeable barriers:they allow particular ions and molecules to pass either into or out of the cell,while preventing the movement of others.Thus the plasma membrane prevents the loss of essential components through leakage while allowing the movement of other molecules.2.Bacterial plasm

3、a membranes play other critical roles.They are the location of several crucial metabolic processes:respiration,photosynthesis,and the synthesis of lipids and cell wall constituents.3.In addition to the plasma membrane,some bacteria have extensive intracytoplasmic membrane systems.These internal memb

4、ranes and the plasma membrane share a basic design.However,they can differ significantly in terms of the lipids and proteins they contain.To understand these chemical differences and the many functions of the plasma membrane and other membranes,it is necessary to become familiar with membrane struct

5、ure.fluid mosaic modelThe model is based on studies of eukaryotic and bacterial membranes,and was established using a variety of experimental approaches,including transmission electron microscopy(TEM)and atomic force microscopyCell membranes are very thin structures,about 5 to 10 nm thick,that look

6、like two dark lines on either side of a light interior when imaged by TEM.Cell membrane by TEMFigure 3.8 The Structure of a Phospholipid.Phosphatidylethanolamine,a phospholipid often found in bacterial membranes.hydrophilic endhydrophobic endIntegral membrane proteins,like membrane lipids,are amphip

7、athic;their hydrophobic regions are buried in the lipid while the hydrophilic portions project from the membrane surfaceProteinsBacterial Lipids Bacterial membranes are similar to eukaryotic membranes in that they are lipid bilayers and many of their amphipathic lipids are phospholipids.The plasma m

8、embrane is very dynamic:the lipid composition varies with environmental temperature in such a way that the membrane remains fluid during growth.For example,bacteria growing at lower temperatures have more unsaturated fatty acids in their membrane phospholipids;that is,there are one or more double co

9、valent bonds in the long hydrocarbon chain.At higher temperatures,their phospholipids have more saturated fatty acids-those in which the carbon atoms are connected only with single covalent bonds.A questionHow the cell membranes help microbes adapt to their inhitats to face different temperatures?A

10、wordlist1.fluid mosaic model 流动镶嵌模型流动镶嵌模型2.Cell contents 细胞内容物细胞内容物3.selectively permeable barriers 选择性渗透屏障选择性渗透屏障4.Molecule 分子分子5.metabolic processes 代谢过程代谢过程6.lipid bilayers脂双层脂双层7.Protein 蛋白质蛋白质8.transmission electron microscopy(TEM)透射电镜透射电镜9.atomic force microscopy 原子力显微镜原子力显微镜10.interior 内部，里面内

11、部，里面11.characteristic 特征，特征性的特征，特征性的12.Appearance 现象，外观现象，外观13.freeze-etching冷冻蚀刻技术冷冻蚀刻技术14.microscopist 显微镜学家显微镜学家15.Phospholipids磷脂磷脂A WORD LIST16.Amphipathic 两亲的，两性分子的两亲的，两性分子的17.Asymmetric 不对称的不对称的18.polar and nonpolar ends 极性和非极性端极性和非极性端19.Hydrophilic 亲水的亲水的20.hydrophobic 疏水的疏水的21.Peripheral membrane proteins 外膜蛋白外膜蛋白22.integral membrane proteins整合蛋白整合蛋白23.electron transport chains电子传递链电子传递链24.saturated fatty acids饱和脂肪酸饱和脂肪酸25.unsaturated fatty acids不饱和脂肪酸不饱和脂肪酸