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会计学Figure1.Schematicdiagramofatypicalprocaryoticcell.Minimally,aprocaryoteiscomposedofacellwallandplasmamembranethatsurroundsitscytoplasmcontainingachromosome,ribosomes,enzymes,severalclassesofRNA,andsmallmolecules(precursors).肽聚糖网格状结构NAG与NAM残基以ß-1,4糖苷键交替连接，形成聚糖的骨架（主链）；一组相同的短肽侧链接于NAM上；相连主链上的短肽侧链通过一条肽桥、或直接相连，从而形成网状分子结构。Figure8.SchematicdiagramofthepeptidoglycansheetofStaphylococcusaureus.G=N-acetyl-glucosamine;M=N-acetyl-muramicacid;L-ala=L-alanine;D-ala=D-alanine;D-glu=D-glutamicacid;L-lys=L-lysine.ThisisonetypeofmureinfoundinGram-positivebacteria.ComparedtotheE.colipeptidoglycan(Figure7)thereisL-lysinplaceofDAP(diaminopimelicacid)inthetetrapeptide.ThefreeaminogroupofL-lysissubstitutedwithaglycinepentapeptide(gly-gly-gly-gly-gly-)whichthenbecomesaninterpeptidebridgeformingalinkwithacarboxygroupfromD-alainanadjacenttetrapeptidesidechain.Gram-positivepeptidoglycansdifferfromspeciestospecies,mainlyinregardstotheaminoacidsinthethirdpositionofthetetrapeptidesidechainandintheaminoacidcompositionoftheinterpeptidebridge.肽聚糖的特点:革兰氏阳性细菌与阴性细菌肽桥的类型
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