c. 生化特征发生变化; d. 以上都是正确的。
15. 真核生物的基因表达调控发生在四个水平上。通过对DNA的甲基化来关闭基因的调控则是属于( )。 a. 染色质活性水平的调控；b. 转录水平调控； c. 转录后加工水平的调控；d. 翻译水平的调控。
四、简答题(选做4题，每题5分，20分)
1. How does regulated secretion differ from constitutive secretion?
2. Dynamic instability causes microtubules either to grow or to shrink rapidly. Consider an individual micro-tubule that is in its shrinking phase. What would happen if the solution contained an analogue of GTP that cannot be hydrolyzed?
3. State the conclusion that can be drawn from the following finding:
When an animal cell is treated with colchicine, its microtubules depolymerize and virtually disappear. If the colchicine is then washed away, the MTs appear again, beginning at the centrosome and elongating outward at about the rate (1 gm/min) at which tubulin polymerizes in vitro.
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、计算与推理(第1题必做，2、3选一题，每题5分，共10分)
1. In an electron micrograph of a human chromosome spread, you observe a thick fiber with a length of about 900 nm and an apparent diameter of 30 nm, which is expected for the solenoid structure of condensed chromatin.
What is the length in base pairs of the double-helical DNA present in this fiber? Assume, for simplicity, that there is one helical turn of the solenoid per 30 nm along the fiber.
2. One of the functions of the mitotic Cdk (the MPF protein kinase) is to cause a precipitous drop in cyclin concentration halfway through M phase. Describe the consequences of this sudden decrease and suggest possible mechanisms by which it might occur.
3. A protein that inhibits certain proteolytic enzymes (proteases) is normally secreted into the bloodstream by liver cells. This inhibitor protein, antitrypsin, is absent from the bloodstream
of patients who carry a mutation that results in a single amino acid change in the protein. Antitrypsin deficiency lung tissue, because of the uncontrolled activity of proteases. Surprisingly, when the mutant antitrypsin is synthesized in the laboratory, it is as active as the normal antitrypsin at inhibiting proteases. Why then does the mutation cause the disease? Think of more than one possibility and suggest ways in which you could distinguish between them.
六、比较题（每题5分，共10分） 1. Compare and contrast the following: cytoplasmic dynein vs. kinesin
2. 后期A与后期B
七、综合问答题(任选一题，20分)
1. 细胞内蛋白质有那些分选途径？各自的机理如何？
2. 比较裂殖酵母、芽殖酵母和哺乳动物细胞周期调控的异同。
八、附加题（每题5分，共15分）
1. State the conclusion that can be drawn from the following finding: Extracts from nondividing frog eggs in the G2 phase of the cell cycle were found to contain structures that could induce the polymerization of tubulin into microtubules in vitro. When examined by immunostaining, these structures were shown to contain pericentrin（中心粒旁侧蛋白）.
2. The signal recognition particle (SKP)) is involved in regulating the elongation of nascent secretory proteins and targeting them to the endoplasmic reticulum. Describe an experiment in which these functions of SRP have been demonstrated.
3. Dephosphorylation is an important event that affects cellular structures during mitosis. Describe two of these events. 试题四参考答案
一、填空题(每空0.5分，共10分)
寡聚糖，内质网，高尔基体，出芽，蛋白包被小泡，笼形蛋白包被小泡，调节型，包被蛋白复合体，组成型，辅基蛋白B-100，受体介导的内吞作用 START
3. 螺线管压缩成超螺线管， 40倍。 4. 基因调节作用
5 ①铁硫蛋白；②辅酶Q；③黄素蛋白；④细胞色素。
二、判断题(正确的标T，错误的标F,或写出必要的答案，共15分) 1.Answer: (a)S ; (b)M ; (c)M; (d)G1 ; (e)M; (f)Gl; (g)Gl, G2, S;``(h)M, G2, S; (i)Gl, S, G2, M;(j)Gl, G2, M 2. 答：T, 正确。
3. 答：错误,粉末状的染色体 4. 答：T,正确。
5.答： F,错误，核纤层蛋白B与内核膜相连。 6 答：F,错误，被阻止在M期。
7. 答：不正确，因为二者的膜蛋白不同。 8. 答：正确。
9. 答：错误, 8个小亚基是核基因编码; 10. 答：错误, 给胞质分裂传递信号
11.答: 错误, 同源染色体间的分子重组是随机发生的。
三、选择题(请将正确答案的代号填入括号，每题1分，共15分) 1. Answer: b 2. Answer: d 3. Answer: b 4.Answer: c 5. Answer: b 6. Answer :D 7. Answer: a 8. Answer: a 9. Answer1.D 10. Answer2.D 11. Answer: C 12. ( d ) 13. ( d )。 14. ( D ) 15. ( A )
四、简答题(选做4题，每题5分，20分)
1. Answer. Regulated secretion occurs only in response to a signal. The proteins to be secreted are stored in special secretory vesicles. Sorting into the regulated secretory pathway is controlled by selective protein aggregation. Constitutive secretion appears to occur by default with secretory proteins, which do not 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. 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 elongation to cease after 70-100 amino acids had been incorporated. When microsomes containing the SRP receptor also were added to the incubations, the block in protein synthesis was relieved and the complete protein minus the signal sequence was extruded into the lumen of the microsomes.
3. Answer:Dephosphorylation events during mitosis include protein phosphatases removing the regulatory phosphates from lamins A, B, and C, permitting reassembly of the nuclear laminae of the two daughter cell nuclei. When MPF activity falls during anaphase, a constitutive phosphatase dephosphory-lares inhibitory sites on myosin light chain, allowing cytokinesis to proceed. 试题五
一、填空题(每空0.5分，共5分)