第5课物质跨膜运输(翟中和第四版).ppt

三、胞吐作用(exocytosis) 胞吐作用是通过分泌泡或其他膜泡与质膜融合而将膜泡内的物质运出细胞的过程 本章小结 小分子、离子的跨膜转运方式 载体蛋白和通道蛋白 简单扩散 被动运输 主动运输 大分子、颗粒物质的胞吞和胞吐 受体介导的内吞 Thank you! 图片来源：/FACULTY/TFischer/bio%201%20files/membrane%20transport.jpg /scitable/content/membrane-transport-into-and-out-of-the* FIGURE 11-29a Proposed structure of GLUT1. (a) Transmembrane helices are represented here as oblique (angled) rows of three or four amino acid residues, each row depicting one turn of the α helix. Nine of the 12 helices contain three or more polar or charged residues (blue or red), often separated by several hydrophobic residues (yellow). This representation of topology is not intended to represent three-dimensional structure. FIGURE 11-31 Model of glucose transport into erythrocytes by GLUT1. The transporter exists in two conformations: T1, with the glucose-binding site exposed on the outer surface of the plasma membrane, and T2, with the binding site exposed on the inner surface. Glucose transport occurs in four steps. 1 Glucose in blood plasma binds to a stereospecific site on T1; this lowers the activation energy for 2 a conformational change from glucoseout ? T1 to glucosein ? T2, effecting the transmembrane passage of the glucose. 3 Glucose is released from T2 into the cytoplasm, and 4 the transporter returns to the T1 conformation, ready to transport another glucose molecule. * Fig. Peter Agre’s experiment with cells containing or lacking aquaporin. The aquaporin is necessary for making the cell absorb water and swell. * * 乌本苷抑制钠钾泵作用机制：乌本苷(ouabain),地高辛(digoxin)等强心剂能抑制心肌细胞Na+-K+泵的活性;从而降低钠钙交换器效率,使内流钙离子增多,加强心肌收缩,因而具有强心作用. * 在 细胞内侧α 亚基与Na+ 相结合促进ATP 水解，α 亚基 上的一个天冬氨酸残基磷酸化引起α 亚基构象发生变 化，将Na+ 泵出细胞，同时细胞外的K+ 与α 亚基的另 一位点结合，使其去磷酸化，α 亚基构象再度发生变化 将K+ 泵入细胞，完成整个循环。从整个转运过程可以 看出，α 亚基的磷酸化发生在Na+ 结合后，而去磷酸化 则发生在K+ 结合后。Na+ 依赖性的磷酸化和K+ 依赖性 的去磷酸化引起Na+-K+ 泵构象发生有序变化，每秒钟可 发生1 000 次左右。此外，每个循环消耗一个ATP 分子， 可以逆着电化学梯度泵出3 个Na+ 和泵入2 个K+ * * /content/168/8/918/F2.expansion * 细胞膜表面LDL受体基因突变，导致LDL受体缺失或异常，体内低密度脂蛋白代谢障碍，血浆总胆固醇和低密度脂蛋白-胆固醇