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1、六细菌细胞结构 Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望Figure 1.Schematic diagram of a typical procaryotic cell.Minimally,a procaryote is composed of a cell wall and plasma membrane that surrounds its cytoplasm containing a chromosome,ribosomes,enzymes,sever
2、al classes of RNA,and small molecules(precursors).（一）细胞壁cell wall:细胞壁的观察方法：细胞壁的观察方法：质壁分离染色质壁分离染色 电镜观察电镜观察G与与G细菌细菌cw的模式结构的模式结构共有组分共有组分 肽聚糖肽聚糖特有组分特有组分 G 磷壁酸磷壁酸 G 脂多糖脂多糖细胞壁是位于菌体的外层，内细胞壁是位于菌体的外层，内侧紧贴细胞膜的一层无色透明，侧紧贴细胞膜的一层无色透明，坚韧而有弹性的结构。细胞壁坚韧而有弹性的结构。细胞壁约占细胞干重的约占细胞干重的10%10%25%25%。Figure 3-Electron micrograp
3、h of a G+cell wall.Figure 4-Electron micrograph of a G-cell wall.细胞壁cell wall:Gram PositiveGram Negative概念：肽聚糖是由概念：肽聚糖是由 N乙酰胞壁酸乙酰胞壁酸（NAM）和和N乙酰葡糖胺乙酰葡糖胺（NAG）以及短肽链（主要是四肽）以及短肽链（主要是四肽）组成的亚单位聚合而成的组成的亚单位聚合而成的大分子聚合物。大分子聚合物。（1）细胞壁的基本骨架肽聚糖（共有成分）肽肽聚糖网格状聚糖网格状结结构构Figure 5-A comparison of L and D amino acids.Note
4、 that while the structure is identical,it is impossible to superimpose them.NAG 与与 NAM 残基以残基以-1,4糖苷糖苷键交替交替连接，形成接，形成聚糖的骨架（主聚糖的骨架（主链）；）；一一组相同的短相同的短肽侧链接于接于NAM上；上；相相连主主链上的短上的短肽侧链通通过一条一条肽桥、或直接相或直接相连，从而形成网状分子，从而形成网状分子结构。构。肽聚糖聚糖单体体网状网状结构构G+菌肽聚糖单体G菌肽聚糖单体Figure 8.Schematic diagram of the peptidoglycan sheet
5、of Staphylococcus aureus.G=N-acetyl-glucosamine;M=N-acetyl-muramic acid;L-ala=L-alanine;D-ala=D-alanine;D-glu=D-glutamic acid;L-lys=L-lysine.This is one type of murein found in Gram-positive bacteria.Compared to the E.coli peptidoglycan(Figure 7)there is L-lys in place of DAP(diaminopimelic acid)in
6、the tetrapeptide.The free amino group of L-lys is substituted with a glycine pentapeptide(gly-gly-gly-gly-gly-)which then becomes an interpeptide bridge forming a link with a carboxy group from D-ala in an adjacent tetrapeptide side chain.Gram-positive peptidoglycans differ from species to species,mainly in regards to the amino acids in the third position of the tetrapeptide side chain and in the amino acid composition of the interpeptide bridge.肽聚糖的特点:1)为原核生物所特有原核生物所特有(古古细菌例外菌例外)2)D-型氨基酸和型氨基酸和DAP在真核在真核细胞中未胞中未发现 3)个个别菌中菌中DAP（二氨基庚二酸）可（二氨基庚二酸）可为Lys代替代替