生物膜结构和功能.ppt

生物膜的结构与功能 ;生物膜（biomembrane）包括质膜和细胞内膜，是极性脂与蛋白质组成的片状超分子复合物，具有独特的结构与功能，是细胞结构的重要组成部分。;;本章内容;1 生物膜功能概述;区隔化或房室化（compartmentalization）;事实上，除了生物膜的区隔化之外，细胞中还有其他的机制使生理途径在空间上隔离开来。;物质的跨膜运输（transport） ;能量转换（energy conversion）;c.“能势膜” 示例;细胞识别（cell recognition）;Fig. 2. Cell surface lectin–carbohydrate interactions. Lectins serve as means of attachment of different kinds of cell as well as viruses to other cells via the surface carbohydrates of the latter. In some cases, cell-surface lectins bind particular glycoproteins (e.g., asialoglycoproteins), whereas in other cases the carbohydrates of cell surface glycoproteins or glycolipids serve as sites of attachment for biologically active molecules that themselves are lectins (e.g. carbohydrate-specific bacterial and plant toxins, or galectins). Based on an original diagram from BioCarbAB (Lund, Sweden).;2 生物膜的化学组成与性质;2.1 膜脂;2.1.1 磷脂（phospholipids, PL）;鞘氨醇磷脂（sphingophospholipids）：;磷脂酰胆碱 鞘磷脂;磷脂中的脂肪酰链： ;顺式构型的不饱和脂肪酸导致分子覆盖面积增大;European Journal of Pharmacology Volume 691, Issues 1–3, 15 September 2012, Pages 1–8;Snake presynaptic neurotoxins with phospholipase A2?activity block nerve terminals in an unknown way. Here, we propose that they enter the lumen of synaptic vesicles following endocytosis and hydrolyse phospholipids of the inner leaflet of the membrane. The transmembrane pH gradient drives the translocation of fatty acids to the cytosolic monolayer, leaving lysophospholipids on the lumenal layer. Such vesicles are highly fusogenic and release neurotransmitter upon fusion with the presynaptic membrane, but cannot be retrieved because of the high local concentration of fatty acids and lysophospholipids, which prevents vesicle neck closure. Trends Biochem Sci. 2000 Jun;25(6):266-70.;磷脂的电荷特性：极性头由带负电荷的磷酸基与带电或不带电的极性基团组成，决定整个磷脂的电荷特性。;生理状态下，磷脂在膜内外分布的不均衡使膜内侧带有额外的负电荷。;C激酶作用途径 可见磷脂酰肌醇的磷???化产物在其中扮演的重要角色;2.1.2 糖脂（glycolipids）;甘油糖脂 糖鞘脂;(A) MGDG (monogalactosyl diacylglycerol, 单半乳糖二酰基甘油). (B) DGDG (dig