【正文】 nd resist flushing ? functioning as invasins (allowing some bacteria to perate host cells ) ? aiding certain bacteria in resisting phagocytic destruction. （ 4）蛋白質(zhì) 在 G細胞壁外層有許多蛋白 PORINS（ 孔蛋白） These are proteins, usually trimeric, that form passive diffusion channels through the outer membrane. Allow molecules of ~600700 Da to pass, but not any macromolecules. Exact position determined by environmental conditions, including osmotic pressure and barometric pressure（氣壓） . Adhesin: The periplasm（外周胞質(zhì)） The periplasm is the gelatinous material between the outer membrane, the peptidoglycan, and the cytoplasmic membrane（質(zhì)膜） . It contains enzymes for nutrient breakdown as well as binding proteins to facilitate the transfer of nutrients across the cytoplasmic membrane. Things found in Periplasmic Space（周質(zhì)空間） : 50100 proteins Binding Proteins: for amino acids, sugars, vitamins, ions Degradative enzymes: phosphatases, proteases, endonucleases Detoxifying enzymes: blactamase（ b內(nèi)酰氨酶 ） (penicillinase) Biosynthesis: peptidoglycan biosynthesis Energy production: cytochromes（細胞色素） Environmental sensing: chemical sensors G細胞壁的外膜是一個滲透屏障 Because of its semipermeable nature, the outer membrane helps retain certain enzymes and prevents some toxic substances, ., penicillin G and lysozyme（ 溶菌酶） from entering. The AcidFast（抗酸細菌） Cell Wall bacteria with an acidfast cell wall resist decolorization with an acidalcohol mixture during the acidfast stain procedure, retain the initial dye carbol fuchsin and appear red. Common acidfast bacteria of medical importance include Mycobacterium tuberculosis（結核分枝桿菌） , Mycobacterium leprae （麻風分枝桿菌） . position: Only relatively small amounts of peptidoglycan are found in the acidfast cell wall. The acidfast cell wall of Mycobacterium contains a large amount of glycolipids such as mycolic acid（分枝菌酸） . A waxy lipid called mycolic acid makes up approximately 60% of the wall and makes the cell wall relatively impermeable. Structure of an AcidFast Cell Wall 分枝菌酸（ mycolic acids） 分枝菌酸是具有分枝的長鏈 β羥基脂肪酸。 磷脂以 磷脂酸乙醇胺 為主，占細胞壁總磷脂的81%，其次是 磷脂酸甘油 占 17%，此外還有少量（約 2%）的 心脂 即二磷脂酰甘油。 endotoxin) from the outer membrane of their cell wall. The LPS binds to a LPSbinding protein circulating in the blood and this plex, in turn, binds to a receptor molecule (CD14 found on the surface of body defense cells called macrophages. This triggers the macrophages to release various defense regulatory chemicals called cytokines, including IL1, IL6, IL8, TNFalpha, and PAF. The cytokines then bind to cytokine receptors on target cells and initiate inflammation and activate both the plement pathways and the coagulation pathway. Physiologic Action of Lipopolysaccharide (LPS) from the GramNegative Cell Wall （ 2）脂蛋白（ lipoproteins） （ 3）磷脂 脂蛋白和磷脂組成了 G細胞壁外層的內(nèi)側 。 類脂 A的結構在不同細菌中有所不同 ， 脂 A有毒性 ， 是一種 內(nèi)毒素 （ endotoxin） 。羥基肉豆蔻酸 。 脂 A是以脂化的葡萄糖胺二糖為單位 ， 通過 焦磷酸鍵 構成的一種獨特糖脂化合物 。 糖的組成或連接方式的不同 —— 抗原性也就不同 核心多糖 組成核心多糖的糖類在不同菌中 變異不大 ，主要是由己糖、庚糖、辛糖酸以及磷酸和乙醇胺組成。 ? aiding certain bacteria in resisting phagocytic destruction. Surface proteins called adhesins in the bacterial cell wall bind to receptor molecules on the surface of a susceptible host cell enabling the bacterium to make intimate contact with the host cell, adhere,colonize, and resist flushing. 革蘭氏陰性細菌 (G)的細胞壁 Structure of a GramNegative Cell Wall 1. a thin, inner wall posed of peptidoglycan (23 nm thick) position: 23 layers of peptidoglycan . Chemically, only 10 to 20% of the gramnegative cell wall is peptidoglycan. function: The peptidoglycan prevents osmotic lysis. 2. an outer membrane position: The outer membrane is a lipid bilayer about 7 nm thick posed of phospholipids, lipoproteins, lipopolysaccharides (LPS), and proteins. outer membrane （ 1）脂多糖（ lipopolysaccharides，簡寫LPS）是 G菌細胞壁特有的成分，位于革蘭氏陰性菌細胞壁的最外側 。 （ 3） surface proteins depending on the strain and species, carry out a variety of activities, including: ? functioning as enzymes。 壁醛酸是由糖醛酸和氨基己糖交替連接而形成的 酸性雜多糖 ，分子結構