1、微生物吸收營(yíng)養(yǎng)物質(zhì)的方式,1、單純擴(kuò)散(simple diffusion or passive diffusion),被輸送的物質(zhì)，靠細(xì)胞內(nèi)外濃度為動(dòng)力，以透析或擴(kuò)散的形式從高濃度區(qū)向低濃度區(qū)的擴(kuò)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 ins

2、ide 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

3、 of its transport needs.,1、單純擴(kuò)散(simple diffusion or passive diffusion),特點(diǎn)： 擴(kuò)散是非特異性的營(yíng)養(yǎng)物質(zhì)吸收方式：如營(yíng)養(yǎng)物質(zhì)通過(guò)細(xì)胞膜中的含水小孔，由高濃度的胞外環(huán)境向低濃度的胞內(nèi)擴(kuò)散； 在擴(kuò)散過(guò)程中營(yíng)養(yǎng)物質(zhì)的結(jié)構(gòu)不發(fā)生變化：即既不與膜上的分子發(fā)生反應(yīng)，本身的分子結(jié)構(gòu)也不發(fā)生變化； 物質(zhì)運(yùn)輸?shù)乃俾瘦^慢：速率與胞內(nèi)外營(yíng)養(yǎng)物質(zhì)的濃度差有關(guān)，即隨細(xì)胞膜內(nèi)外該物質(zhì)濃度差的降低而減小，直到胞內(nèi)外物質(zhì)濃度相同； 不需要載體參與； 擴(kuò)散是一個(gè)不需要代謝能的運(yùn)輸方式：因此，物質(zhì)不能進(jìn)行逆濃度運(yùn)輸。 可運(yùn)送的養(yǎng)料有限：限于水、溶于水的氣體，及

4、分子量小，脂溶性、極性小的營(yíng)養(yǎng)物質(zhì)。,smosis,flows towards high salt concentrations,單純擴(kuò)散模式圖,細(xì)胞膜外,細(xì)胞膜內(nèi),細(xì)胞膜,三營(yíng)養(yǎng)物通過(guò)與細(xì)胞膜上載體蛋白（也稱作透過(guò)酶permease）的可逆性結(jié)合來(lái)加快其傳遞速度,促進(jìn)擴(kuò)散 (facilitated diffusion/transport),Facilitated diffusion utilizes membrane protein channels to allow charged molecules (which otherwise could not diffuse across th

5、e 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 g

6、radient.,促進(jìn)擴(kuò)散(facilitated diffusion),特點(diǎn)：在促進(jìn)擴(kuò)散過(guò)程中 營(yíng)養(yǎng)物質(zhì)本身在分子結(jié)構(gòu)上也不會(huì)發(fā)生變化 不消耗代謝能量，故不能進(jìn)行逆濃度運(yùn)輸 運(yùn)輸?shù)乃俾视砂麅?nèi)外該物質(zhì)的濃度差決定 需要細(xì)胞膜上的載體蛋白（透過(guò)酶）參與物質(zhì) 運(yùn)輸 被運(yùn)輸?shù)奈镔|(zhì)與載體蛋白有高度的特異性 養(yǎng)料濃度過(guò)高時(shí), 與載體蛋白出現(xiàn)飽和效應(yīng) 促進(jìn)擴(kuò)散的運(yùn)輸方式多見(jiàn)于真核微生物中，例如通常在厭氧生活的酵母菌中，某些物質(zhì)的吸收和代謝產(chǎn)物的分泌是通過(guò)這種方式完成的。,Embeded protein:,Proteins that act as carriers are too large to move

7、 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.,or active ansport,主動(dòng)運(yùn)輸(Active transport),在代謝能的推動(dòng)下，通過(guò)膜上特殊載體 蛋白逆養(yǎng)料濃度梯度吸收營(yíng)養(yǎng)物質(zhì)的過(guò)程,主動(dòng)運(yùn)輸(Active transport),特點(diǎn)：物質(zhì)在主動(dòng)運(yùn)輸?shù)倪^(guò)程中 需要消耗代

8、謝能 可以進(jìn)行逆濃度運(yùn)輸?shù)倪\(yùn)輸方式 需要載體蛋白參與 對(duì)被運(yùn)輸?shù)奈镔|(zhì)有高度的立體專一性 被運(yùn)輸?shù)奈镔|(zhì)在轉(zhuǎn)移的過(guò)程中不發(fā)生任何化學(xué)變化 不同的微生物在主動(dòng)運(yùn)輸過(guò)程中所需的能量的來(lái)源不同，好氧微生物中直接來(lái)自呼吸能，厭氧微生物主要來(lái)自化學(xué)能，光合微生物中則主要來(lái)自光能 。 主動(dòng)運(yùn)輸是微生物吸收營(yíng)養(yǎng)物質(zhì)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 direc

9、tly 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 tran

10、sport, 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 passiv

11、e transport.,主動(dòng)運(yùn)輸模式圖,細(xì)胞膜,細(xì)胞膜外,細(xì)胞膜內(nèi),恢復(fù)原構(gòu)象,移位,再循環(huán),結(jié)合,構(gòu)象改變,Na+-K+-ATP酶系統(tǒng),Na+-K+-ATPase是存在于原生質(zhì)膜上的一種重要離子通道蛋白 功能: 利用ATP能量將Na+由細(xì)胞內(nèi)“泵”出胞外,并將K+“泵”入胞內(nèi)。 該酶由大小兩個(gè)亞基組成（MW: 12萬(wàn), 5.5萬(wàn)）,作用步驟: 1. ATP酶(E)在細(xì)胞內(nèi)側(cè)與3個(gè)Na+結(jié)合,同時(shí)消耗能量; 2. 磷酸化ATP酶(E+)構(gòu)象變化將Na+排除胞外,并與2個(gè)K+ 結(jié)合; 3. K+激發(fā)E+脫磷酸化恢復(fù)為E, 同時(shí)將K+運(yùn)入細(xì)胞.,基因轉(zhuǎn)位是一種特殊的主動(dòng)運(yùn)輸，與普通的主動(dòng)運(yùn)輸相比

12、，營(yíng)養(yǎng)物質(zhì)在運(yùn)輸?shù)倪^(guò)程中發(fā)生了化學(xué)變化（糖在運(yùn)輸?shù)倪^(guò)程中發(fā)生了磷酸化）。其余特點(diǎn)與主動(dòng)運(yùn)輸相同。 基因轉(zhuǎn)位主要存在于厭氧和兼性厭氧型細(xì)菌中，也主要是用于單（或雙）糖與糖的衍生物，以及核苷與脂肪散的運(yùn)輸,基團(tuán)轉(zhuǎn)位(Group translocation),在酶的作用下HPr被激活,在酶的作用下P-HPr將磷酸轉(zhuǎn)移給糖,運(yùn)送機(jī)制:是依靠磷酸轉(zhuǎn)移酶系統(tǒng),即磷酸烯醇式丙酮酸-己糖磷酸轉(zhuǎn)移酶系統(tǒng). 運(yùn)送步驟: 1.熱穩(wěn)載體蛋白(HPr)的激活 細(xì)胞內(nèi)高能化合物磷酸烯醇式丙酮酸（PEP）的磷酸基團(tuán)把HPr激活。 酶1 PEP+HPr 丙酮酸+P-HPr HPr是一種低分子量的可溶性蛋白，結(jié)合在細(xì)胞膜上，具

13、有高能磷酸載體的作用。,2、糖被磷酸化后運(yùn)入膜內(nèi) 膜外環(huán)境中的糖先與外膜表面的酶2結(jié)合，再被轉(zhuǎn)運(yùn)到內(nèi)膜表面。這時(shí)，糖被P-HPr上的磷酸激活，并通過(guò)酶2的作用將糖-磷酸釋放到細(xì)胞內(nèi)。 酶2 P-HPr+糖 糖-P +HPr 酶2是一種結(jié)合于細(xì)胞膜上的蛋白，它對(duì)底物具有特異性選擇作用，因此細(xì)胞膜上可誘導(dǎo)出一系列與底物分子相應(yīng)的酶2。,四種運(yùn)輸營(yíng)養(yǎng)物質(zhì)方式的比較,Special Cases 1. Endocytosis 2. Exocytosis,There are four types of carrier-mediated transport systems in procaryotes. T

14、he 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

15、 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 t

16、ransport (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 e

17、nter 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 ty

18、pe 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 th

19、e 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

20、 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

21、 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 t

22、he 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 transpo

23、rt 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 channe

24、l. 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-depe

25、ndent 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 ch