4. 什么是蛋白质N-连接糖基化和O-连接糖基化？发生在何种部位？
5. 过氧化物酶体是怎样进行氧浓度调节的?有什么意义?
五、看图描述(每题10分，共20分)
1. 根据对核蛋白运输机制的研究及相关蛋白的发现, 提出了核蛋白的输入模型(图 1), 请对这一模型作出文字说明(PCC1:Ran nucleotide-exchange factor1)。
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图1 含有NLS信号的核蛋白从细胞质输入细胞核的推测模型
2. 图2 是关于MPF的活性调节，请作出文字说明：
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图2. 酵母MPF的活性调节
六、综合题(20分):
生物膜是怎样合成的?可能的机理是什么?
七、附加题（只能选做15分题） 1. 分析思考（5分）
基因的转录加工和蛋白质的合成是遗传信息流的两个关键环节，对此细胞核与细胞质有明确的分工：细胞核负责基因的转录加工，而细胞质则负责完成蛋白质的合成。核糖体是合成蛋白质的工厂， 由大小两个亚基组成，它们都是在细胞核着中装配的。从细胞的生命活动看，在长期的进化过程中选择了经济合理的路线，但是在核糖体的装配中却选择了一种违背经济规律的做法：组成核糖体大小亚基的80余种蛋白质在胞质溶胶中合成之后被运送到细胞核中；在核仁中装配成的核糖体大、小亚基又要被运送到胞质溶胶中，它们是核输出中体积最大的物质。由于细胞中核糖体的数量巨大，组成核糖体的rRNA的种类和数量都远比组成核糖体的蛋白
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质少，如果细胞核将合成好的rRNA运送到胞质溶胶中，在那里进行核糖体的装配和蛋白质的合成岂不更经济合理？假如是这种情况的话，有哪些不利？谈谈您的看法。
2.（5分） Consider the v-SNAREs that direct transport vesicles from the trans Golgi network to the plasma membrane. They, like all other v-SNAREs, are membrane proteins that are integrated into the membrane of the ER during their biosynthesis and are then transported by transport vesicles to their destination. Thus, transport vesicles budding from the ER contain at least two kinds of v-SNAREs--those that target the vesicles to the cis Golgi cisternae and those that are in transit to the trans Golgi network to be packaged in different transport vesicles destined for the plasma membrane. (A) Why might this be a problem? (B) Suggest possible ways in which the cell might solve it.
3 （10分）。 Specialization of membranes is a characteristic of mammalian cells. What are the mechanisms by which the apical and basolateral surfaces of certain cells become differentiated?
4.(5分) Many mutant yeasts have been isolated that are defective in the control of their cell cycle. They proliferate normally at low temperatures (300C)but show abnormal patterns of cell growth and division when grown at a higher temperature (370C). Two mutant strains (called \“wee\different sites in the same gene have very different responses to elevated temperature. Gee strain cells grow until they become enormous but no longer divide. Wee strain cells have very short cell cycles and divide when they are very much smaller than usual. Suggest a possible model to explain these observations, and suggest what the normal protein encoded by this gene might do.
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