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1、Arrangements of lipids in aqueous media,Hydrophobic surfaces such as fatty acyl chains aggregate in aqueous solutions. Caused by aversion of water molecules to hydrophobic surfaces which force the water into ordered structures. Alternative structures with the hydrophobic surfaces as compact as possi
2、ble, are favored.,脂质体,单膜小泡,多膜小泡,双层体,Liposome （脂质体） Liposome are highly stable structures that can be subjected to manipulations such as gel filtration chromatography and dialysis. With such methods, it is possible to prepare liposome having different inside and outside solution compositions. Liposom
3、e can be used as drug and enzyme delivery systems in therapeutic applications. For example, liposome can be used to introduces contrast agents into the body for diagnostic imaging procedures, including computerized tomographic (CT) and magnetic resonance imaging (MRI). Liposome can fuse with cells,
4、mixing their contents with the intracellular medium. If methods can be developed to target liposomes to selected cell populations, it may be possible to deliver drugs, therapeutic enzymes, and contrast agents to particular kinds of cells (such as cancer cells) （药物靶）,2. Protein: 蛋白质是组成微生物细胞膜的另一重要成分，可
5、占细胞膜干重的50-65。 按存在的位置分为：,镶嵌蛋白,外周蛋白,细菌视紫红质,细菌视紫红蛋白（bacteriorhodopsin ) 这种蛋白是嗜盐菌紫膜中所特有的，约占膜重的75%，分子量为26 000Da。每分子蛋白上有一分子视黄醛与多肽链的一个赖氨酸结合在一起，成为具有紫红色的蛋白质。每分子细菌视紫红蛋白有7段-螺旋结构组成，每段-螺旋结构长约4nm，横跨细胞膜，而使细胞膜上呈现出六角形格的规则排列,the 3D structure of bacteriorhodopsin (cross section of the structural model. Selected residu
6、es important for proton transfer steps are marked. The probable path of protons is indicated by arrows.,the sequence of bacteriorhodopsin written to show the seven transmembrane helices and the extracellular and intracellular loops. The extracellular surface is at the bottom.,E,I,In all these cases,
7、 the portion within the lipid bilayer consists primarily of hydrophobic amino acids. These are usually arranged in an alpha helix so that the polar -C=O and -NH groups at the peptide bonds can interact with each other rather than with their hydrophobic surroundings. Those portions of the polypeptide
8、 that project out from the bilayer tend to have a high percentage of hydrophilic amino acids. Furthermore, those that project into the aqueous surroundings of the cell are usually glycoproteins, with many hydrophilic sugar residues attached to the part of the polypeptide exposed at the surface of th
9、e cell. Some transmembrane proteins that span the bilayer several times form a hydrophilic channel through which certain ions and molecules can enter (or leave) the cell.,Trs130 can be extracted from the P100 fraction by salt, but not by detergent.,Trs130 is a membrane-associated protein,肉豆蔻酰C14,异戊二
10、烯基,棕榈酸,肉豆蔻酸,脂肪族氨基酸,糖基磷脂酰肌醇,Carrier proteins are peripheral proteins which do not extend all the way through the membrane. They move specific molecules through the membrane one at a time.,Channel proteins extend through the bilipid layer. They form a pore through the membrane that can move molecules
11、in several ways.,按照功能分：A. 运输蛋白（Transport Proteins）,identify the cell/compartment to others,B. Marker proteins,Marker proteins extend across the cell membrane and serve to identify the cell. The immune system uses these proteins to tell friendly cells from foreign invaders. They are as unique as fing
12、erprints.,C. Receptor Proteins,allow the cell to receive instructions,These proteins are used in intercellular communication. In this animation you can see a hormone binding to the receptor. This causes the receptor protein release a signal to perform some action,D. Enzymes 膜中酶蛋白的种类十分丰富，聚集了关于细胞壁、荚膜和
13、细胞膜合成的酶类，某些水解酶类如脂酶、蛋白酶和肽酶等，呼吸酶类和电子传递链中的各种电子传递体，和ATP酶,ATP酶,二、细胞膜的结构流体镶嵌模型（fluid mosaic model）,膜变窄,Membrane fluidity: Frye-Edidin experiment,Frye-Edidin experiment,Frye-Edidin experiment,Membrane Bilayer Mobility Proteins could move rapidly in biological membranes (Frye-Edidin experiments) Many membra
14、ne proteins can move laterally across a membrane at a rate of a few microns per minute. On the other hand, some integral membrane proteins are much more restricted in their lateral movement, with diffusion rates of about 10nm/sec or even slower.,Lipids also undergo rapid lateral motion in membrane .
15、 A typical phospholipid can diffuse laterally in a membrane at a rate of several um/sec. At that rate, a phospholipid could travel from one end of a bacterial cell to the other in less than a second or traverse a typical animal cell in a few minutes. On the other hand, transverse movement of lipid o
16、r protein from one face of bilayer to the other is much slower ( and much less likely),Lipid movements in membranes,Bond rotation (1012 - 1013/sec),Translational motion (microns/sec),Rotational diffusion (108 - 109/sec),Bilateral motion or flip-flop (days/event),翻转酶,翻转酶,Ca2+ induce phase separation
17、in membranes formed from phosphatidylserine (PS) 磷脂酰丝氨酸 and phosphatidylethanolamine (PE)磷脂酰乙醇胺 or from PS, PE, and phosphatidylcholine (PC) 磷脂酰胆碱 . Ca2+ added to these membranes forms complexes with the negatively charged serine carboxyl, causing the PS to cluster and separate from the other lipids
18、. Such metal-induced lipid phase separation has been shown to regulate the activity of membrane-bound enzymes.,Membranes Are Asymmetric Structures,1. Lateral Asymmetry （横向不对称）,Membrane lipid asymmetry,PC,PE,PS,SM,2. Transverse Asymmetry （横向不对称）,(神经)鞘磷脂,三、细胞质（cytoplasm） 细胞质无色透明，呈溶胶状态，形成结构复杂的三维网状系统，由细
19、胞膜伸展至核区。细胞质的主要成分为水、蛋白质、核酸、脂类，还有少量糖和无机盐。由于富含核酸，因而嗜碱性强。幼龄菌细胞质含RNA多，电子密度较高。老龄菌细胞质的RNA含量少，电子密度较低。细胞质中，存在有单位膜包被的间体和空泡，或仅有单层蛋白质包被的贮存颗粒，如聚-羟基丁酸颗粒、糖原颗粒、羧酶体（carboxsome）和蛋白质结晶等，有的根本没有膜包被。,细胞质的主要功能是： 为各种细胞器维持其正常结构及其存在、各种酶系统及其催化生化反应提供所需要的空间、理化环境和一切底物，并容纳各生化反应的产物。一旦由于细胞膜破裂，细胞质即泄漏或流失，细胞必将死亡。,四、核糖体（ribosome）,第二节 微
20、生物细胞的外部结构 一、表面附属物（surface appendages） （一）、鞭毛、菌毛和性毛 1、细菌的鞭毛（bacterial flagella）,螺旋菌,Detecting Bacterial Motility Since motility is a primary criterion for the diagnosis and identification of bacteria, several techniques have been developed to demonstrate bacterial motility, directly or indirectly. 1.
21、 flagellar stains outline flagella and show their pattern of distribution. If a bacterium possesses flagella, it is presumed to be motile,Flagellar stains of three bacteria a. Bacillus cereus b. Vibrio cholerae c. Bacillus brevis (CDC). Since the bacterial flagellum is below the resolving power of t
22、he light microscope, although bacteria can be seen swimming in a microscope field, the organelles of movement cannot be detected. Staining techniques such as Leifsons method utilize dyes and other components that precipitate along the protein filament and hence increase its effective diameter. Flage
23、llar distribution is occasionally used to differentiate between morphologically related bacteria. For example, among the Gram-negative motile rod-shaped bacteria, the enterics have peritrichous flagella while the pseudomonads have polar flagella.,2. motility test medium demonstrates if cells can swi
24、m in a semisolid medium. A semisolid medium is inoculated with the bacteria in a straight-line stab with a needle. After incubation, if turbidity (cloudiness) due to bacterial growth can be observed away from the line of the stab, it is evidence that the bacteria were able to swim through the medium
25、.,(a) G-细菌 （b）G+细菌,鞭毛丝（FILAMENT ）: 成分为鞭毛蛋白（flagellin） 鞭毛亚单位的分子量介于30,000-60,000Da之间。 一个种的鞭毛丝一般由一种鞭毛蛋白亚单位组成，极少有两种鞭毛蛋白亚单位组成。不同菌种的鞭毛蛋白的氨基酸组成不同，但共同点是都不含半胱氨酸和色氨酸，脯氨酸、酪氨酸和组氨酸的含量也很低。 鞭毛蛋白具有抗原特异性，称为H抗原。,鞭毛钩（HOOK） 直径17nm，长约900nm，约占鞭毛干重的l 是由一种蛋白亚单位组成 蛋白亚单位的分子量因种而异，例如E. coli，Salmonella typhimurium的分子量为42 000Da
26、鞭毛钩蛋白亚单位的氨基酸中，苯丙氨酸和蛋氨酸的含量较高,基体（BASAL BODY） 蛋白由9-10种分子量在9,000Da-60,000Da之间的多肽链亚单位装配而成。,(a) G-细菌 b）G+细菌,（2）功能：鞭毛是细菌的运动器官 运动时以M环为转子带动中轴和鞭毛丝旋转；S环、P环和L环，起固定轴瓦的作用，允许中轴在其中央孔中旋转。推动M环转动的动力来自细胞质膜内外的质子浓度梯度，即膜内外的质子运动力，当质子自外（或内）流向内（或外）时，便推动M环旋转，每旋转一圈据推算需要256个质子。,Two proteins in the flagellar motor, called MotA a
27、nd MotB, form a proton channel through the cytoplasmic membrane and rotation of the flagellum is driven by a proton gradient. This driving proton motive force occurs as protons accumulating in the space between the cytoplasmic membrane and the cell wall as a result of the electron transport system t
28、ravel through the channel back into the bacteriums cytoplasm.,The bacterial flagellum can rotate both counterclockwise and clockwise. This is controlled by a protein switch in the molecular motor of the basal body. Clockwise rotation results in a tumbling motion and changes the direction of bacteria
29、l movement. On the other hand, counterclockwise rotation leads to long, straight or curved runs without a change in direction. During a run, that lasts about one second, the bacterium moves 10- 20 times its length before it stops. In the case of a tumble, the movement lasts only about one-tenth of a
30、 second and no real forward progress is made.,当鞭毛逆时针转动时，细菌作直线运动，顺时针转动时，细菌就翻腾转向。这与鞭毛蛋白亚单位以左手螺旋的方向而成为鞭毛丝有关。鞭毛逆时针转动也是向左转动，致使细菌后部的鞭毛扭成一束，进行逆时针外转动，而推动细菌前进。当鞭毛作顺时针（向右）转动时，鞭毛便散开，而引起翻腾转向。,细菌的趋化性,a. 无刺激物时，E.coli 翻腾时改变运动方向,a.,Motility serves to keep bacteria in an optimum environment via taxis. Taxis is a mot
31、ile response to an environmental stimulus. Bacteria can respond to chemicals (chemotaxis), light (phototaxis), osmotic pressure (osmotaxis), oxygen (erotaxis), and temperature (thermotaxis).,Chemotaxis is a response to a chemical gradient of attractant or a repellent molecules in the bacteriums envi
32、ronment. In an environment that lacks such a gradient, the bacterium moves randomly. It travels in a straight line, or runs, for a few seconds, then stops, tumbles, and runs in a different direction. However, when the bacterium is exposed to a chemical gradient of, for example, an attractant, it tum
33、bles less frequently (has longer runs) as it moves up the gradient, but tumbles at the normal rate if it travels down the gradient. In this way, the net movement is towards a more optimum environment.,微生物趋化性的机理 基粒作为发动机可驱动鞭毛杆作顺时针和逆时针方向转动。M环包含FliG, MotA 和MotB 蛋白。用于驱动M环转动的能量来源于MotA 和MotB形成的通道所产生的质子动力。M
34、otB也起着将M环固定在细胞壁中肽聚糖层的作用。 FliG 蛋白在接受来自甲基受体趋化蛋白MCPs（methyl accepting chemotaxis proteins）的信号后作顺时针或逆时针方向转动。,2、细菌的菌毛（fimbriae）,菌毛是广泛存在于革兰氏阴性细菌和某些革兰氏阳性细菌菌体表面的一层由短且直的毡状物细丝，原叫繖毛（fimbriae），现多称菌毛（pili）。 菌毛由菌毛蛋白组成，菌毛蛋白的氨基酸组成与鞭毛蛋白的不同。 根据菌毛的形态和功能，可分为数个类型：体菌毛、极菌毛和束菌毛等。,超微结构表明菌毛都是由不同数量的螺旋线空心圆柱体。 体菌毛、极菌毛和束菌毛的菌毛蛋白单
35、位数量、螺旋线和中空圆柱体的内外径各不相同。 革兰氏阴性菌的菌毛着生于细胞膜，伸出周质间隙和细胞壁。革兰氏阳性菌的菌毛附着于细胞的位置尚不清楚。菌毛具有较强的再生能力。,菌毛的功能并非运动，而是用于附着基物，也与致病性有关。 致病性细菌以菌毛粘附到组织细胞、粘膜细胞和精子细胞的表面上，这是致病菌侵染宿主的第一步。l型菌毛还能引起血细胞凝集作用。但某些细菌如不动杆菌（Acinetobacter）的极菌毛可使细胞作颤动式运动。黄色粘球菌的菌毛可引起滑动式运动。,Bacteria Altering the Adhesive Tips of Their Pili,3、细菌的性菌毛（sex pili）
36、一般认为性菌毛也是菌毛的一类，只是由于其较普通菌毛长而粗直一些而有别于普通菌毛，而且具有使“雌”、“雄”细菌接合的功能。性毛的直径较菌毛的直径粗，较鞭毛的细，约为9-10nm，长而直，数目少，1-3根。,大肠杆菌的性毛分两型： 一型称为F pili，长可达20m。编码形成F pili的基因位于F质粒上 另一型较短，称I pili，不超过2m，直径为7nm。编码形成I plli的基因位于Col I和R质粒上。 F菌毛是由菌毛蛋白单体组成的4条同轴螺旋线，装配成外径8nm，内径2nm和螺距为12.8nm的空心圆柱体。F菌毛在内膜中装配，穿过外膜伸展到细胞表面。构成性菌毛的蛋白称为性菌毛蛋白（pil
37、in）。大肠杆菌性毛蛋白亚单位的分子量为11 800Da，含124个氨基酸，但缺组氨酸、脯氨酸和半胱氨酸。但每分子性菌毛蛋白含有2分子磷酸和1分子葡萄糖。,4、真核微生物的鞭毛和纤毛 某些低等水生真菌和藻类的游动孢子以及许多原生动物的细胞表面有鞭毛，单极生或双极生。有些原生动物，如草履虫细胞表面着生很多纤毛（cilia）。鞭毛和纤毛都是运动器官，二者内部结构相似，只不过鞭毛长（150m），纤毛短（5-10m），二者直径相似，约为0.15-0.3m，光学显微镜下，勉强可见。,（1）结构 鞭毛和纤毛主要由鞭杆（shaft）和基体（basal body）两部分所组成。鞭杆和基体之间有一过渡区。鞭杆伸
38、出细胞之外，基体埋于细胞膜中。鞭杆外有一层单位膜包围，此膜与细胞质膜相连。,鞭杆,基体,过渡区,鞭杆的横切面如图，中央有一对微管，由中央鞘包着；外围环绕有9对二联体（doublets）。微管的这种排列，被称为92型结构 基体又称生毛体或动体，呈短杆状，在电镜下观察，直径约120-170nm，长为200-500nm，横切面观察，可见外围有9个三联体，中央没有微管和鞘，为90型。,（2）功能 真核细胞的鞭毛或纤毛的功能是运动，但与细菌鞭毛的运动方式完全不同，它们是以波浪形摆动（鞭打）以推动细胞前进，而不是像细菌鞭毛那样转动。,（二）、荚膜（capsule）和粘液层（slime layer）,在形态
39、上它们可以分为二类： 大荚膜（macrocapsules），在光学显微镜下可见，至少0.2m厚，有明确的外界面。 微荚膜（microcapsules），厚度小于0.2m，因此在光学显微镜下看不见，但用免疫学的方法可以测出它们的存在。是否真有微荚膜是有争论的，有人认为组成微荚膜的物质是细胞壁的一种成分； 粘液层，它积累在微生物细胞的表面而没有特定的形态结构。产生荚膜的微生物也时常产生粘液层，其组成成分不同于荚膜。在培养液中常会有组成粘液层的物质。,1、化学组成 水是荚膜和粘液层的主要组分，多糖是最常见的荚膜和粘液层的有机成分。 Capsules are generally composed of
40、 polysaccharide; rarely they contain amino sugars or peptides （1）同型多糖（homopolysaccharides） Leuconostoc所产生的葡聚糖（glucans）。葡聚糖主要以（16）键连接，具有分枝的葡萄糖多聚体，除（16）键外，也有些（13）和（14）键。它可作为血浆代用品。,（2）杂型多糖（heteropolysaccharides） Pseudomonas aeruginosa的胞外多糖是由D-葡萄糖，D-半乳糖，D-甘露糖，L-鼠李糖和D-葡萄糖醛酸构成的酸性多糖。 由于细菌胞外多糖具有抗原性，因此医学临床诊断
41、上常用血清学方法对病原菌进行鉴定作快速诊断。,（2）杂型多糖（heteropolysaccharides） Pseudomonas aeruginosa的胞外多糖是由D-葡萄糖，D-半乳糖，D-甘露糖，L-鼠李糖和D-葡萄糖醛酸构成的酸性多糖。 由于细菌胞外多糖具有抗原性，因此医学临床诊断上常用血清学方法对病原菌进行鉴定作快速诊断。,2、功能 碳源和能源贮藏物质 并能保护细胞免受干燥的影响 由于能抗宿主吞噬细胞的吞噬和噬菌体的侵染，增强了某些病原菌的致病能力。例如能引起肺炎的肺炎双球菌型，如果失去了荚膜，则成为非致病菌。 mediate adherence of cells to surfac
42、es. biofilm,Some bacteria produce slime materials to adhere and float themselves as colonial masses in their environments. Other bacteria produce slime materials to attach themselves to a surface or substrate. Bacteria may attach to surface, produce slime, divide and produce microcolonies within the
43、 slime layer, and construct a biofilm, which becomes an enriched and protected environment for themselves and other bacteria. A classic example of biofilm construction in nature is the formation of dental plaque (牙菌斑 ) mediated by the oral bacterium, Streptococcus mutans 链球菌.,（三）、点阵颗粒（lattice granul
44、e） 许多细菌和一些蓝细菌（Cyanobacteria）都有覆盖整个或部分细胞壁表面的规则排列的大分子颗粒晶体层，大多数仅有一层晶体层，也可有两层重叠但排列不同的晶体层，此称为点阵颗粒。 例如，海洋亚硝化胞囊菌（Nitrosocystis oceanus）的两个晶体层，分别为六角形和直线形排列。腐蛤螺菌（Spirillum putridiconchylium）的细胞表面，球形颗粒以线状排列成外层，较大颗粒以四角形排列成内层，并以规则式样相互联合，结合到细胞壁脂多糖层凹坑的外表面。,空肠弯曲菌(Campylobacter jejuni)表面的点阵颗粒（）负染 (a) 145 000, (b) 1
45、75 000,（四）、外膜泡（outer membrane vesicle） 在扫描电镜下和负染标本中，均可见到革兰氏阴性细菌细胞表面或周围，经常存在着大小悬殊、形状多样的突起物或脱落物。球状、管状及其两者相结合的复合体。,A. 副百日咳博德特菌 (Bordetella para pertussis),B. 铜绿假单胞菌 （Pseudomonas aeruginosa）,(a) 大小外膜泡复合体（*） (b) 增生的多层外膜泡（*）,T株霍乱弧菌(Vibrio cholerae T-variant)的外膜泡,对于外膜泡的形成机理，Wensink（1981）认为由于外膜合成速度超过了肽聚糖层的合
46、成速度，外膜便与下面的肽聚糖层局部分离，并向胞外凸出，逐渐膨胀成球状，或不断伸长成管状，或形成两者的联合体。成熟的外膜泡，在基部收缩合拢后便自细胞上脱落，成为游离的外膜泡 . 外膜泡的主要化学成分是脂多糖（LPS）。 外膜泡似有防御性作用，细胞通过释放外膜泡可摆脱吸附的噬菌体。含有细菌素（bacteriocin）的外膜泡，能直接抵御噬菌体和其它原核微生物的侵袭。,（五）、螺管结构（coil structure） 个别细菌细胞有一种粗大中空而不易弯曲的菌毛样附属物，这种细丝具有间距12nm、并与垂直线倾斜7度的横向条纹，形成一条螺旋形细丝，螺旋细丝外覆一个管状鞘膜，被称为螺管结构 。,黄疸出血型
47、钩端螺旋体(Leptospera icterohaemorrhagiae)的螺管结构 (a) 负染，88,000一段螺线（）从鞘管断开处（）脱出，失去螺线的这段鞘管变成狭窄（），(b) a图的高倍放大，负染 292,000,螺管结构起源于细胞壁，鞘膜由外膜延伸而来，但与细胞膜之间无结构上的联系，这不同于菌毛和鞭毛。螺管结构易自细胞上脱落和失去鞘膜。有鞘膜的螺管结构直径6065nm，长13m，基部呈喇叭形。无鞘膜的，呈螺旋线圈状，直径3840nm。螺旋线圈易被拉开和压扁。 螺管结构目前仅发现于钩端螺旋体属中，其功能尚不清楚,S-layer： Many gram-negative and gram
48、-positive bacteria, as well as many Archaea possess a regularly structured layer called an S-layer attached to the outermost portion of their cell wall. It is composed of protein or glycoprotein and in electron micrographs, has a pattern resembling floor tiles.,Characteristic properties of S-layer p
49、roteins S-layers are composed of a single protein or glycoprotein species (Mw 40-200 kDa) and exhibit either oblique, square or hexagonal lattice symmetry with unit cell dimensions in the range of 3 to 30 nm. S-layers are generally 5 to 10 nm thick and show pores of identical size (diameter, 2 - 8 nm) and morphology. S-layer proteins show a remarkably difference in surface corrugation (皱) and chemistry between inner and outer face. The topography of the inner face