a. have very similar structures and bind to 20.缬氨霉素是一种可形成通道的离子载体 能够使(a)的运输速度提 the same receptor. b bind to receptors with different 高100,000倍。 C Ca2+.dH+ and-binding sites but similar 四、简答题(每题4分,选做5题,共20分) c. bind to different receptors and activate 1. Describe the similarities and differences in the cycling of G, different second messengers and Ras between the active and inactive d bind to the same receptors, one being forms Answer 1: Binding of hormone to its intracellular and the other receptor causes a con-formational change extracellular in the receptor The receptor then binds 答b to gm protein cau change in the Gsa protein and release of the 17. Which mutant form of ras is likely to cause bound GDP. GTP then binds to Gsa which causes release of the GTP-Gsa complex from malignancy? the B and r subunits. The GTP-Gsa complex ras that cannot hydrolyze gTP then activates adenylyl cyclase. Activatio b. ras that cannot bind to gtp intrinisic GTPase activity in G c. ras that cannot bind to Grb2 or Sos hydrolyzes gtp to GDP and returns G to its inactive torm. d. ras that cannot bind to raf 答:a 2.如何理解"被动运输是减少细胞与周围环境 The sequence of events that occurs after 的差别而主动运输则是努 insulin binds to its receptor 力创造差别维持生命的活力”? 答:主要是从创造差异对细胞生命活动的意义 a. binding of IRS-> phosphorylation of 方面来理解这一说法。主动运输涉及物质输入 proteins with SH2 domains -> effect 和输出细胞和细胞器并且能够逆浓度梯度或 binding of proteins with SH2 domains-> 电化学梯度。这种运输对于维持细胞和细胞器 phosphorylation of IRs->effect 的正常功能来说起三个重要作用①保证了细 c. autophosphory lation 胞或细胞器从周围环境中或表面摄取必需的 IRs->binding of proteins 营养物质即使这些营养物质在周围环境中或 with sh2 domains - effect 表面的浓度很低②能够将细胞内的各种物质 autophosphorylation and binding of IRs 如分泌物、代谢废物以及一些离子排到细胞外, phosphorylation of proteins 即使这些物质在细胞外的浓度比细胞内的浓 with sH2 domains ->effect 19.下列连接方式中属于与中间纤维相连的锚度高得多能够维持些无机离子在细胞内 定连接的是(c)。 恒定和最适的浓度特别是K+Ca2+和H+的浓 a.粘合带;b.粘合斑 度。概括地说,主动运输主要是维持细胞内环 C.桥粒 d.紧密连接。 境的稳定以及在各种不同生理条件下细胞内5 a. have very similar structures and bind to the same receptor. b. bind to receptors with different ligand-binding sites but similar functions. c. bind to different receptors and activate different second messengers. d. bind to the same receptors, one being intracellular and the other, extracellular. 答:b 17. Which mutant form of ras is likely to cause malignancy? a. ras that cannot hydrolyze GTP b. ras that cannot bind to GTP c. ras that cannot bind to Grb2 or Sos d. ras that cannot bind to Raf 答:a 18. The sequence of events that occurs after insulin binds to its receptor tyrosine kinase is: a. binding of IRS -> phosphorylation of proteins with SH2 domains -> effect b. binding of proteins with SH2 domains -> phosphorylation of IRS -> effect c. autophosphorylation and phosphorylation of IRS -> binding of proteins with SH2 domains -> effect d. autophosphorylation and binding of IRS -> phosphorylation of proteins with SH2 domains -> effect 19. 下列连接方式中属于与中间纤维相连的锚 定连接的是( c )。 a．粘合带； b．粘合斑； c．桥粒； d．紧密连接。 20. 缬氨霉素是一种可形成通道的离子载体, 能够使( a )的运输速度提 高 100,000 倍。 a.K+ ; b.Na+ ; c.Ca2+ ; d.H+ 四、简答题(每题 4 分， 选做 5 题，共 20 分) 1 ． Describe the similarities and differences in the cycling of Gs and Ras between the active and inactive forms. Answer 1:. Binding of hormone to its receptor causes a con-formational change in the receptor. The receptor then binds to Gm protein causing a conformational change in the Gs protein and release of the bound GDP. GTP then binds to Gs which causes release of the GTP-Gs complex from the  and  subunits. The GTP-Gs complex then activates adenylyl cyclase. Activation is short-lived because the intrinisic GTPase activity in Gs hydrolyzes GTP to GDP and returns G~ to its inactive form. 2. 如何理解“被动运输是减少细胞与周围环境 的差别,而主动运输则是努 力创造差别,维持生命的活力”? 答: 主要是从创造差异对细胞生命活动的意义 方面来理解这一说法。主动运输涉及物质输入 和输出细胞和细胞器,并且能够逆浓度梯度或 电化学梯度。这种运输对于维持细胞和细胞器 的正常功能来说起三个重要作用:① 保证了细 胞或细胞器从周围环境中或表面摄取必需的 营养物质,即使这些营养物质在周围环境中或 表面的浓度很低;② 能够将细胞内的各种物质, 如分泌物、代谢废物以及一些离子排到细胞外, 即使这些物质在细胞外的浓度比细胞内的浓 度高得多; ③能够维持一些无机离子在细胞内 恒定和最适的浓度,特别是 K+、Ca2+和 H+的浓 度。概括地说，主动运输主要是维持细胞内环 境的稳定,以及在各种不同生理条件下细胞内