1、MCB 细胞信号转导 练习题 1 一问答题 1. （True/False） There is no fundamental distinction between signaling molecules that bind to cell-surface receptors and those that bind to intracellular receptors. Explain your answer. False. Signaling molecules that bind to cell-surface receptors do not have to cross the plasm
2、a membrane; thus, they can be large or small, hydrophilic or hydrophobic. By contrast, signaling molecules that bind to intracellular receptors must be sufficiently small and hydrophobic to diffuse across the plasma membrane. 2. G-protein-linked receptors activate G proteins by reducing the strength
3、 of GDP binding, allowing GDP to dissociate and GTP, which is present at much higher concentrations, to bind. How do you suppose the activity of a G protein would be affected by a mutation that caused its affinity for GDP to be reduced without significantly changing its affinity for GTP? The mutant
4、G protein would be constantly active. Each time the subunit hydrolyzed GTP to GDP, the GDP would spontaneously dissociate, allowing GTP to bind and reactive the subunit. Normally, GDP is tightly bound by the subunit, which keeps the G protein in its inactive state until release of GDP is stimulated by interaction with an appropriate G-protein-linked receptor.
