大学考研 食品专业 双语课件_Lecture_3.pdf

Lecture 3-3 Microbial cell biology Cell Structure and Function School of Life Science and Biotechnology Shanghai Jiao Tong University 3.8 Cell Wall of Prokaryotes Peptidoglycan and Related Molecules 原核生物细胞壁原核生物细胞壁 肽聚糖与相关分子肽聚糖与相关分子 Protoplasts原生质体原生质体 a In dilute solution breakdown of the cell wall releases the protoplast, but it immediately lyses because the cytoplasmic membrane is very weak. 稀溶液中原生质体会立即破裂. Protoplasts原生质体原生质体 b In a solution containing an isotonic concentration of a solute such as sucrose, water does not enter the protoplast and it remains stable.等渗溶液中, 水不进入原生质体, 原生质体稳定. Shanghai Jiao Tong University Shanghai Jiao Tong University What is a cell wall for A wall is for against pressure-2 atm A wall is for maintaining cell shape A wall is for giving cells rigidity Shanghai Jiao Tong University Shanghai Jiao Tong University Gram stain革兰氏染色革兰氏染色 This staining has long been used for classifying and identifying bacteria For more detail Lecture 3-1 Steps in the Gram stain procedure.革兰氏染色过程 结晶紫染1分钟 碘液媒染3分钟 酒精脱色20秒 沙黄复染1-2分钟 FLASH Examples of Gram Staining Differences in cell wall structure are at the base of differences in the Gram-staining reaction. The G- cell wall is a multilayered structure and quite complex, whereas the G cell wall consists of primarily a single type of molecule and is often much thicker. Cell walls of Bacteria FLASH Shanghai Jiao Tong University Shanghai Jiao Tong University 4.8.1 Peptidoglycan 4.8.1 Peptidoglycan 肽聚糖肽聚糖 Cell wall of Bacteria have one rigid layer to strengthen the wall. The rigid layer of G and G- Bacteria is peptidoglycan layer.肽聚糖层肽聚糖层 In G- Bacteria, additional layers are present outside this rigid layer. Peptidoglycan unit is composed of two suger derivatives, N- acetylglucosamineand N-acetylmuramic acid, and a small group of amino acids consisting of L-alanine, D-alanine, D-glutamic acid, and either lysine or diaminopimelic acid DAP.肽聚糖由肽聚糖由N N- -乙酰葡萄糖胺和乙酰葡萄糖胺和- -乙酰胞壁酸加上一组氨乙酰胞壁酸加上一组氨 基酸组成基酸组成DAPDAP二氨基庚二酸二氨基庚二酸 How the peptide and glycan units are connected to the peptidoglycan sheet. a No interbridge in gram-negative Bacteria. b Glycine interbridge in gram-positive Bacteria.G菌的肽聚糖单位之间有甘氨酸五肽桥, 而G-菌无五肽桥. c Overall structure of peptidoglycan. G, N-acetylglucosamine; M, N-acetylmuramic acid 4.8.2 The structure of Gram positive bacterial cell walls One thick peptidoglycan layer 25 sheets Teichoic acids （磷壁酸）（磷壁酸） Polymers containing glycerolphosphate or ribitol phosphate residues 含在磷酸甘油及磷酸核糖醇的多聚物含在磷酸甘油及磷酸核糖醇的多聚物 Lipoteichoic acids teichoic acids that covalently bound to membrane lipids脂磷壁酸脂磷壁酸 与膜脂类共价连接的磷壁酸与膜脂类共价连接的磷壁酸 The cell walls of gram-positive cells contain mostly peptidoglycan. The cell walls of gram-positivecells are smoother than that of gram-negativecells. Shanghai Jiao Tong University Shanghai Jiao Tong University 4.9 The Outer Membrane of Gram Negative Bacteria Two membranes Outer membrane外膜外膜 Cytoplasmic membrane细细 胞质膜胞质膜 One thin peptidoglycan layer一层肽聚糖层一层肽聚糖层 Periplasm space周质空周质空 间间 One out of cell bounded space Porin Although the outer membrane is often called the second lipid bilayer, the chemistry and architecture of this layer differs in many ways from that of the cytoplasmic membrane The gramThe gram- -negative cell wall.negative cell wall. Shanghai Jiao Tong University Shanghai Jiao Tong University Structure of the lipopolysaccharide LPS of G- bacteria.脂多糖 O-specific polysaccharide varies among species.O-特异多糖 Core polysaccharide 核心多糖 Lipid A 类脂A The surface texture of a G-cell is heavily folded when compared with a Gcell. Shanghai Jiao Tong University Shanghai Jiao Tong University Relationship of Cell Wall Structure to the Gram Stain PhenomenonIn Gram stain, an insoluble crystal violet- iodine complexis ed inside the cell, and the complex is extracted by alcoholfrom G- but not from G Bacteria. Reason G Bacteria, which have very thick peptidoglycan layer, become dehydrated by the alcohol. This causes the pores in the walls to close, preventing the insoluble crystal violet-iodine complex from escaping. G菌的厚肽聚糖层菌的厚肽聚糖层 被乙醇脱水被乙醇脱水, 造成壁上小孔收缩造成壁上小孔收缩,从而使不溶性的结晶从而使不溶性的结晶 紫紫-碘复合物不能洗出碘复合物不能洗出. Then, what happened to G- Bacteria Shanghai Jiao Tong University Shanghai Jiao Tong University In G- Bacteria, alcohol readily penetrates the lipid-rich outer layer, and the thin peptidoglycan layer also does not prevent solvent passage, thus, the crystal violet-iodine complex is easily removed. G-菌中菌中, 乙醇很容易穿透富脂的乙醇很容易穿透富脂的 外膜外膜, 薄的肽聚糖壁也无法阻止溶剂的通过薄的肽聚糖壁也无法阻止溶剂的通过. Shanghai Jiao Tong University Shanghai Jiao Tong University How can cell wall become the target for killing a cell Peptidoglycan Structure Lysozyme -1,4 glycosidic bond is sensitive to lysozyme肽聚糖的肽聚糖的 -1,4糖苷链对溶菌酶敏感糖苷链对溶菌酶敏感 Peptidoglycan synthesis Penicillin The first commercialized and still most important antibiotic青霉素青霉素 Transport of peptidoglycan precursorswas send to the growing point of the cell wall across the cytoplasmic membrane 细菌萜醇 The transpeptidationreaction that leads to the final cross- linking of two peptidoglycan chains转肽作用转肽作用 Shanghai Jiao Tong University Shanghai Jiao Tong University Penicillin and lysozyme Penicillin inhibitor of transpeptidation 抑制转肽作用抑制转肽作用 Create imbalance between the action of autolysin and transpeptidation 造成自溶与转肽作用的不平衡造成自溶与转肽作用的不平衡 Can only kill actively growing cells Lysozyme Break exisiting glycosidic bonds Lead to cell burst Create protoplast or spheroplast Shanghai Jiao Tong University Shanghai Jiao Tong University