中山大学生科院：《细胞生物学》2000级期末试卷_04（带答案）.doc_大学文库

selectively aggregate being included 氧张力增强而成正比地提高(图7-44)。因此在 transport vesicles. 低浓度氧的条件下,线粒体利用氧的能力比过 Answer 氧化物酶体强但在高浓度氧的情况下,过氧化 f Gtp is present but cannot be hydrolyzed,物酶体的氧化反应占主导地位这种特性使过 microtubules will continue 氧化物酶体具有使细胞免受高浓度氧的毒性 to grow until all free tubulin subunits have作用 Answer 五、计算与推理(第1题必做,2、3选一题 The cen trason serves as 每题5分,共10分) vivo and There are six nucleosomes per helical turn of all of the microtubules rad iat ing from the the solenoid structure, and one helical turn of corresponds to slightly less than the same polari 30nm the length of a chromatin thick 4.答:加在于粗面内质网上合成的蛋白质上 fiber. Assuming, for simplicity of calculation, one 的糖基可由两种途径连接:通过天冬氨酸残基 helical turn per30mm, then there are6 的N原子或通过丝氨酸和苏氨酸残基的O原 nucleosomes per30- nm stretch of thick fiber. A 子。N连结糖蛋白合成的第一步在粗面内质网900 thick fiber thus has 30 solenoid 上进行,糖链是从磷酸多萜醇转移至新生肽链turs nm divided by 30 nm/turn) and 上。这种糖基化在高尔基体中继续被修饰。O- contains180 nucleosomes(6 nucleosomes/turn 连结的糖基化是在高尔基体中进行的。 X 30 turms). The DNA content of each human ucleosome plus the linker DNA connecting it to 5答:过氧化物酶体中的氧化酶都是利用分子 djacent nucleosomes is about 200 bp. This thick 氧作为氧化剂,催化下面的化学反应 fiber thus contains 36,000 bp of DNA: (200 RH2+02 ---------R+H,O3 bp/nucleosome) X(180 nucleosomes/900-nm 这一反应对细胞内氧的水平有很大的影 thick fiber 响。例如在肝细胞中有20%的氧是由过氧化物酶体消耗的其余的在线粒体中消耗。在过氧化2. Answer 物酶体中氧化产生的能量以产热的方式消耗 oss of cycl in leads to inactivation of the 掉,而在线粒体中氧化产生的能量贮存在ATP itotic Cdk. As the result, its target prote 中。线粒体与过氧化物酶体对氧的敏感性是不 become dephosphorylated by phosphatases,and 一样的线粒体氧化所需的最佳氧浓度为2%6左 the cells exit mitosis- they disassemble the 右增加氧浓度并不提高线粒体的氧化能力。 mitotic spindle, reassemble the nuclear 过氧化物酶体与线粒体不同,它的氧化率是随 evelope, decondense their chromosomes, and so

2 selectively aggregate being included in transport vesicles. 2. Answer If GTP is present but cannot be hydrolyzed, microtubules will continue to grow until all free tubulin subunits have been used up. 3. Answer: The centrosome serves as a microtubule-organizing center in vivo, and all of the microtubules radiating from the centrosome apparently have the same polarity. 4. 答：加在于粗面内质网上合成的蛋白质上的糖基可由两种途径连接：通过天冬氨酸残基的 N 原子或通过丝氨酸和苏氨酸残基的 O 原子。N-连结糖蛋白合成的第一步在粗面内质网上进行，糖链是从磷酸多萜醇转移至新生肽链上。这种糖基化在高尔基体中继续被修饰。O- 连结的糖基化是在高尔基体中进行的。 5.答: 过氧化物酶体中的氧化酶都是利用分子氧作为氧化剂, 催化下面的化学反应: RH2 + O2 ---------→ R + H2O2 这一反应对细胞内氧的水平有很大的影响。例如在肝细胞中,有 20%的氧是由过氧化物酶体消耗的,其余的在线粒体中消耗。在过氧化物酶体中氧化产生的能量以产热的方式消耗掉, 而在线粒体中氧化产生的能量贮存在 ATP 中。线粒体与过氧化物酶体对氧的敏感性是不一样的,线粒体氧化所需的最佳氧浓度为 2%左右,增加氧浓度,并不提高线粒体的氧化能力。过氧化物酶体与线粒体不同, 它的氧化率是随氧张力增强而成正比地提高(图 7-44)。因此,在低浓度氧的条件下,线粒体利用氧的能力比过氧化物酶体强,但在高浓度氧的情况下,过氧化物酶体的氧化反应占主导地位,这种特性使过氧化物酶体具有使细胞免受高浓度氧的毒性作用。五、计算与推理(第 1 题必做，2、3 选一题，每题 5 分，共 10 分) 1. Answer： There are six nucleosomes per helical turn of the solenoid structure, and one helical turn of the solenoid corresponds to slightly less than 30nm along the length of a chromatin thick fiber.Assuming, for simplicity of calculation, one helical turn per 30 nm, then there are 6 nucleosomes per 30-nm stretch of thick fiber. A 900-nm-long, thick fiber thus has 30 solenoid turns (900 nm divided by 30 nm/turn) and contains 180 nucleosomes (6 nucleosomes/turn ×30 turns).The DNA content of each human nucleosome plus the linker DNA connecting it to adjacent nucleosomes is about 200 bp. This thick fiber thus contains 36,000 bp of DNA: (200 bp/nucleosome) × (180 nucleosomes/900-nm thick fiber). 2. Answer： Loss of cyclin leads to inactivation of the mitotic Cdk. As the result, its target proteins become dephosphorylated by phosphatases, and the cells exit mitosis--they disassemble the mitotic spindle, reassemble the nuclear envelope, decondense their chromosomes, and so

on. Cycl in is degraded by ubiq- uitin-dependent microtubules, although only dynein occurs on the destruction in proteosomes, and the activation of microtubules of cilia and flagella. Kinesin is a e mitotic Cak most likely causes the plus-end directed micro tubular motor, and dynein ubiquitination of the cyclin, but with a substantial among its other roles, is a minus-end directed delay. As discussed in Chapter 5, ubiquitination microtubu lar motor. In spite of their similarities tags proteins for degradation in proteasomes in function, they are not homologous proteins, assume quite different Answer: The actual explanation is that the three-dimensional shapes. They are not members single amino acid change causes the protein to ora proteinfamily 后期A与后期B ented by aperone proteins in the er from ex iting this danelle. t therefore accumulates in the ER七、综合问答题任选一题,20分) 1.答:翻译后转运与共翻译转运 men and is eventually degraded. Alternative 跨膜运输 terpretations might have been: (1)the mutation affects the stability of the protein in the 小泡运输核孔运输 bloodstream so that it is degraded much faster in the blood than the normal protein, or(2)the 2. mutation inactivates the ER signal sequence and 同:有关卡,有周期蛋白与周期蛋白激酶异:CDC2CDC28哺乳动物不同的激酶与多 prevents the protein from entering the ER. ( 3) nother explanation could have been that the种周期蛋白。 retention hich would have 八、附加题(每题5分,共15分) 1. Answer: The extracts appear to R. One could d isting structures that are functionally equivalent to centrosomes (as evidenced by between using the presence of pericentrin) antibodies against the protein nucleate microtubule growth. to follow its transport in the cells(see Panel 5-3, 2. Answer: The functions of sRP were pp.158-159) demonstrated in a series of experiments cell-free protein-synthesizing system and mRNA 六、比较题(每题5分,共10分) encoding pre-prolactin, a typical 1. Answe secretory protein. When the mRNA was incubated in the cell-free translational Both dynein and kinesin are large motor system in the absence of SRP and microsomes proteins that convert the chemical energy of ATp the complete prot tein with its signa sequence was produced. The addition of SRP into movement. Both are found affiliated with to the incubation mixtures caused protein

3 on. Cyclin is degraded by ubiq-uitin-dependent destruction in proteosomes, and the activation of the mitotic Cdk most likely causes the ubiquitination of the cyclin, but with a substantial delay. As discussed in Chapter 5, ubiquitination tags proteins for degradation in proteasomes. 3. Answer：The actual explanation is that the single amino acid change causes the protein to misfold slightly so that, although it is still active as a pro-tease inhibitor, it is prevented by chaperone proteins in the ER from exiting this organelle. It therefore accumulates in the ER lumen and is eventually degraded. Alternative interpretations might have been: (1) the mutation affects the stability of the protein in the bloodstream so that it is degraded much faster in the blood than the normal protein, or (2) the mutation inactivates the ER signal sequence and prevents the protein from entering the ER. (3) Another explanation could have been that the mutation altered the sequence to create an ER retention signal, which would have retained the mutant protein in the ER. One could distinguish between these possibilities by using fluorescent-tagged antibodies against the protein to follow its transport in the cells (see Panel 5-3, pp. 158-159). 六、比较题（每题 5 分，共 10 分） 1. Answer: Both dynein and kinesin are large motor proteins that convert the chemical energy of ATP into movement. Both are found affiliated with microtubules, although only dynein occurs on the microtubules of cilia and flagella. Kinesin is a plus-end directed microtubular motor, and dynein, among its other roles, is a minus-end directed microtubular motor. In spite of their similarities in function, they are not homologous proteins, and they assume quite different three-dimensional shapes. They are not members ora proteinfamily. 2. 后期 A 与后期 B 七、综合问答题(任选一题，20 分) 1. 答：翻译后转运与共翻译转运跨膜运输小泡运输核孔运输 2. 答：同：有关卡，有周期蛋白与周期蛋白激酶；异：CDC2,CDC28,哺乳动物不同的激酶与多种周期蛋白。八、附加题（每题 5 分，共 15 分） 1. Answer: The extracts appear to contain structures that are functionally equivalent to centrosomes (as evidenced by the presence of pericentrin), which nucleate microtubule growth. 2. Answer:The functions of SRP were demonstrated in a series of experiments utilizing a cell-free protein-synthesizing system and mRNA encoding pre-prolactin, a typical secretory protein. When the mRNA was incubated in the cell-free translational system in the absence of SRP and microsomes, the complete protein with its signal sequence was produced. The addition of SRP to the incubation mixtures caused protein