(精品)微生物学课件26

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,*,微生物吸收营养物质的方式,1、单纯扩散(,simple diffusion or passive diffusion),被输送的物质，靠细胞内外浓度为动力，以透析或扩散的形式从高浓度区向低浓度区的扩散。,Simple diffusion means that the molecules can pass directly through the membrane. Diffusion is always down a concentration gradient. This limits the maximum possible concentration of the molecule inside the cell (or outside the cell if it is a waste product). The effectiveness of diffusion is also limited by the diffusion rate of the molecule. Therefore, though diffusion is an effective enough transport mechanism for some substances (such as H2O), the cell must utilize other mechanisms for many of its transport needs.,1、单纯扩散(,simple diffusion or passive diffusion),特点：,扩散,是非特异性的,营养物质吸收方式,：如营养物质通过细胞膜中的含水小孔，由高浓度的胞外环境向低浓度的胞内扩散；,在扩散过程中营养物质的结构不发生变化,：即既不与膜上的分子发生反应，本身的分子结构也不发生变化；,物质运输的速率较慢：,速率,与胞内外营养物质的浓度差有关，即随细胞膜内外该物质浓度差的降低而减小，直到胞内外物质浓度相同；,不需要载体参与,；,扩散是一个不需要代谢能的运输方式：,因此，物质不能进行逆浓度运输。,可运送的养料有限：,限于水、溶于水的气体，及,分子量小，脂溶性、极性小的营养物质。,smosis,flows towards high salt concentrations,单纯扩散模式图,细胞膜外,细胞膜内,细胞膜,三,营养物通过与细胞膜上载体蛋白（也称作透过酶,permease,）,的可逆性结合来加快其传递速度,促进扩散,(,facilitated diffusion/transport),Facilitated diffusion utilizes membrane protein channels to allow charged molecules (which otherwise could not diffuse across the cell membrane) to freely diffuse in a,nd,out of the cell. These channels comes into greatest use with small ions like K+, Na+, and,Cl,-. The speed of facilitated transport is limited by the number of protein channels available, whereas the speed of diffusion is dependent only on the concentration gradient.,促进扩散,(,facilitated diffusion),特点：在促进扩散过程中,营养物质本身在分子结构上也不会发生变化,不消耗代谢能量，故不能进行逆浓度运输,运输的速率由胞内外该物质的浓度差决定,需要细胞膜上的载体蛋白（透过酶）参与物质 运输,被运输的物质与载体蛋白有高度的特异性,养料浓度过高时, 与载体蛋白出现饱和效应,促进扩散的运输方式多见于真核微生物中，例如通常在厌氧生活的酵母菌中，某些物质的吸收和代谢产物的分泌是通过这种方式完成的。,Embeded,protein:,Proteins,that act as,carriers,are too large to move across the membrane. They are,transmembrane,proteins. They cycle between,two conformations,in which a solute binding site is accessible on one side of the membrane or the other.,促进扩散模式图,细胞膜,细胞膜外,细胞膜内,恢复原构象,移位,再循环,结合,结合,构象改变,or active,ansport,主动运输(,Active transport),在代谢能的推动下，通过膜上特殊载体,蛋白逆养料浓度梯度吸收营养物质的过程,主动运输(,Active transport),特点：物质在主动运输的过程中,需要消耗代谢能,可以进行逆浓度运输的运输方式,需要载体蛋白参与,对被运输的物质有高度的立体专一性,被运输的物质在转移的过程中不发生任何化学变化,不同的微生物在主动运输过程中所需的能量的来源不同，好氧微生物中直接来自呼吸能，厌氧微生物主要来自化学能，光合微生物中则主要来自光能 。,主动运输是微生物吸收营养物质的主要方式。,Comparison of passive and active transport.,Legend:,If uncharged solutes are small enough, they can move down their concentration gradients directly across the lipid,bilayer,itself by simple diffusion. Examples of such solutes are ethanol, carbon dioxide, and oxygen. Most solutes, however, can cross the membrane only if there is a membrane transport protein (a carrier protein or a channel protein) to transfer them. As indicated, passive transport, in the same direction as a concentration gradient, occurs spontaneously, whereas transport against a concentration gradient (active transport) requires an input of energy. Only carrier proteins can carry out active transport, but both carrier proteins and channel proteins can carry out passive transport,.,主动运输模式图,细胞膜,细胞膜外,细胞膜内,恢复原构象,移位,再循环,结合,构象改变,ADP+Pi,ATP,Na,+,-K,+,-ATP,酶系统,Na,+,-K,+,-,ATPase,是,存在于原生质膜上的一种重要离子通道蛋白,功能:,利用,ATP,能量将,Na,+,由细胞内“泵”出胞外,并将,K,+,“泵”入胞内。,该酶由大小两个亚基组成（,MW: 12,万, 5.5万）,作用步骤:,1. ATP,酶(,E),在细胞内侧与3个,Na,+,结合,同时消耗能量;,2.,磷酸化,ATP,酶(,E,+,),构象变化将,Na,+,排除胞外,并与2个,K,+,结合;,3.,K,+,激发,E,+,脱磷酸化恢复为,E,同时将,K,+,运入细胞.,基因转位是一种特殊的主动运输，与普通的主动运输相比，营养物质在运输的过程中发生了化学变化（糖在运输的过程中发生了磷酸化）。其余特点与主动运输相同。,基因转位主要存在于厌氧和兼性厌氧型细菌中，也主要是用于单（或双）糖与糖的衍生物，以及核苷与脂肪散的运输,基团转位(,Group translocation),在酶的作用下,HPr,被激活,在酶的作用下,P-,HPr,将磷酸转移给糖,运送机制,:是依靠磷酸转移酶系统,即磷酸烯醇式丙酮酸-己糖磷酸转移酶系统.,运送步骤:,1.热稳载体蛋白(,HPr,),的激活,细胞内高能化合物磷酸烯醇式丙酮酸（,PEP）,的磷酸基团把,HPr,激活。,酶1,PEP+,HPr,丙酮酸+,P-,HPr,HPr,是一种低分子量的可溶性蛋白，结合在细胞膜上，具有高能磷酸载体的作用。,2、糖被磷酸化后运入膜内,膜外环境中的糖先与外膜表面的酶2结合，再被转运到内膜表面。这时，糖被,P-,HPr,上的磷酸激活，并通过酶2的作用将,糖-磷酸,释放到细胞内。,酶2,P-,HPr,+,糖 糖-,P +,HPr,酶2是一种结合于细胞膜上的蛋白，它对底物具有特异性选择作用，因此细胞膜上可诱导出一系列与底物分子相应的酶2。,基团移位,模式图,细胞膜外,细胞膜内,S,S,S,S,细胞膜,Enz2,Enz2,Enz2,Enz2,S,S,HPr,P,P,HPr,Enz1+,PEP,丙酮酸,四种运输营养物质方式的比较,比较项目,单纯扩散,促进扩散,主动运输,基团转位,特异载体蛋白,运输速度,物质运输方向,胞内外浓度,运输分子,能量消耗,运输后物质的结构,无,慢,由浓至稀,相等,无特异性,不需要,不变,有,快,由浓至稀,相等,特异性,不需要,不变,有,快,由稀至浓,胞内浓度高,特异性,需要,不变,有,快,由稀至浓,胞内浓度高,特异性,需要,改变,Special Cases,1.,Endocytosis,2.,Exocytosis,There are four types of carrier-mediated transport systems in,procaryotes,. The carrier is a protein (or group of proteins) that function in the passage of a small molecule from one side of a membrane to another. A transport system may be a single,transmembranous,protein that forms a channel that admits passage of a specific solute. Or a transport system may be a coordinated system of proteins that binds and sequentially passes a small molecule through membrane. Transport systems have the property of specificity for the solute transported. Some transport systems transport a single solute with the same specificity and kinetics as an enzyme. Some transport systems will transport (structurally) related molecules, although at reduced efficiency compared to their primary substrate. Most transport systems transport specific sugars, amino acids, anions or,cations,that are of nutritional value to the bacterium.,Figure 12. Transport processes in bacterial cells. Solutes enter or exit from bacterial cells by means of one of three processes:,uniport,symport,(also called,cotransport,) and,antiport,(also called exchange diffusion). Transport systems (Figure 13 below) operate by one or another of these processes.,Facilitated diffusion systems (FD) are the least common type of transport system in bacteria. Actually, the glycerol,uniporter,in E.,coli,is the only well known facilitated diffusion system. FD involves the passage of a specific solute through a carrier that forms a channel in the membrane. The solute can move in either direction through the membrane to the point of of equilibrium on both sides of the membrane. Although the system is carrier-mediated and specific, no energy is expended in the transport process. For this reason the glycerol molecule cannot be accumulated against the concentration gradient.,Facilitated diffusion systems (FD),Ion driven transport systems,(IDT) and,Binding-protein dependent transport systems,(BPDT) are,active transport systems,that are used for transport of most solutes by bacterial cells. IDT is used for accumulation of many ions and amino acids; BPDT is frequently used for sugars and amino acids. IDT is a,symport,or,antiport,process that uses a hydrogen ion (H+) i.e., proton motive force (,pmf,), or some other,cation, i.e.,chemiosmotic,potential, to drive the transport process. IDT systems such as the lactose,permease,of,E.,coli,utilize the consumption of a hydrogen ion during the transport of lactose. Thus the energy expended during active transport of lactose is in the form of,pmf,. The lactose,permease,is a single,transmembranous,polypeptide that spans the membrane seven times forming a channel that specifically admits lactose.,Binding-protein dependent transport systems, such as the,histadine,transport system in,E.,coli, are composed of four proteins. Two proteins form a membrane channel that allows passage of the,histadine,. A third protein resides in the,periplasmic,space where it is able to bind the amino acid and pass it to a forth protein which admits the amino acid into the membrane channel. Driving the solute through the channel involves the expenditure of energy, which is provided by the hydrolysis of ATP.,Group translocation systems,(GT), more commonly known as the,phosphotransferase,system,(,PTS,) in,E.,coli, are used primarily for the transport of sugars. Like binding protein-dependent transport systems, they are composed of several distinct components. However, GT systems specific for one sugar may share some of their components with other group transport systems. In,E.,coli, glucose may be transported by a group translocation process that involves the,phosphotransferase,system. The actual carrier in the membrane is a protein channel fairly specific for glucose. Glucose specifically enters the channel from the outside, but in order to exit into the cytoplasm, it must first be,phosphorylated,by the,phosphotransferase,system. The PTS derives energy from the metabolic intermediate,phosphoenol pyruvate,(PEP). PEP is hydrolyzed to,pyruvate,and glucose is,phosphorylated,to form glucose-phosphate during the process. Thus, by the expenditure of a single molecule of high energy phosphate, glucose is transported and changed to glucose-phosphate.,Group translocation systems,(GT),Table 7. Distinguishing characteristics of bacterial transport systems.,PD = passive diffusion,FD = facilitated diffusion,IDT = ion-driven transport,BPDT = binding protein dependent transport,GT = group translocation,Property,PD,FD,IDT,BPDT,GT,carrier mediated,-,+,+,+,+,conc. against gradient,-,-,+,+,NA,specificity,-,+,+,+,+,energy expended,-,-,pmf,ATP,PEP,solute modified during transport,-,-,-,-,+,Table 7. Distinguishing characteristics of bacterial transport systems,