微生物學-04-原核與真核細胞的功能剖析.ppt

Prokaryotic Cells原核細胞 Learning Objective 4-1 Compare and contrast the overall cell structure of prokaryotes and eukaryotes. Comparing Prokaryotic and Eukaryotic Cells： Prokaryote comes from the Greek words for prenucleus. Eukaryote comes from the Greek words for true nucleus. Prokaryote Eukaryote One circular chromosome, not in a membrane No histones No organelles Peptidoglycan cell walls Binary fission The size, shape, and arrangement of bacterial cell Average size：0.2~2.0 μm ? 2~8 μm Basic shapes： Unusual shapes Star-shaped Stella Square Haloarcula Most bacteria are monomorphic A few are pleomorphic Arrangements Pairs： diplococci， diplobacilli Clusters：staphylococci Chains： streptococci， streptobacilli Arrangements Structure of Bacteria Structural External to the Cell WallGlycocalyx（醣膠層） Outside cell wall Usually sticky A capsule is neatly organized A slime layer is unorganized loose Extracellular polysaccharide allows cell to attach Capsules prevent phagocytosis Flagella鞭毛 Outside cell wall Made of chains of flagellin. Attached to a protein hook. Anchored to the wall and membrane by the basal body. Flagella Arrangement鞭毛的排列方式 Motile Cells Rotate flagella to run or tumble Move toward or away from stimuli (taxis) Flagella proteins are H antigens (e.g., E. coli O157:H7) Axial Filaments（軸絲） Endoflagella In spirochetes Anchored at one end of a cell Rotation causes cell to move Fimbriae allow attachment Pili are used to transfer DNA from one cell to another Cell Wall（細胞壁） Prevents osmotic lysis Made of peptidoglycan (in bacteria) 細胞壁的結構 細胞壁的主要成分： Peptidoglycan Peptidoglycan之 基本構造： (a) Glycan backbone： 由N-acetylglucosamine (NAG) 與N-acetylmuramic acid (NAM) 約10~65個醣分子交替連接所組成的骨架(排, rows)。 (b) pentapeptide： 由四個胺基酸組成的short peptide與上述rows(排)骨架 之N-acetylmuramic acid 相連。 (c) Cross-bridge 由Transpeptidase 將上述之兩個鄰近側鏈間相連。 Composition：Peptidoglycan Polymer of disaccharide