细胞生物学资料：细胞课前训练题

1、2006细胞课Q&AQBy daisy2006.9.51. Your next-door neighbor has donated $20 in support of cancer research and in horrified to learn that her money is being spent on studying brewers yeast. How could you put her mind at ease?(1)、参考答案：为什么你的邻居会有这种担心？(2)、参考答案：为什么要假设？2. an adult human is composed of about 1013

2、 cells, all of which are derived by cell division from a single fertilized egg.A. Assuming that all cells continue to divide (like bacteria in rich media). How many generations of cell divisions would be required to produce 1013 cells?B. Human cells in culture divide about once per day. Assuming all

3、 cells continue to divide at this rate during development, how long would it take to generate an adult organism?C. Why is it, do you think, that adult human take longer to develop than calculations might suggest?2006.9.121. Friedrich Miescher (1844-1895), Gregor Mendel (1822-1884), Louis Pasteur (18

4、22-1895), and Rudolf Virchow (1821-1902) were European scientists (from Switzerland, Austria, France, and Germany, respectively) whose most important discoveries were made in the 20-year period from 1855 to 1875. assume that the four men met at a scientific conference in 1875 to discuss their respec

5、tive contributions to biology.(a) What might the four scientists have found they had in common?(b) What do you think Pasteur might have found most intriguing or relevant about Virchows work? Explain your answer.(c) What do you think Virchow might have found most intriguing or relevant about Mendels

6、work? Explain your answer.(d) In whose work do you think Miescher might have been the most interested? Explain your answer.答：(a) The four scientists might have found that they had common interests in the origin of cells (from preexisting cells, not by “spontaneous generation) and the nature of the g

7、enetic information that organisms pass on to their progeny. (Bear in mind, however, that we are answering the question from the perspective of almost 125 years of further discoveries and insights. In 1875, the four scientists might with equal likelihood have concluded that they had few, if any, inte

8、rests in common.)(b) Given Pasteurs demonstration that living, preexisting yeast cells are needed to carry out the fermentation of sugar into alcohol, he would almost certainly have been interested in Virchows conclusion that all cells come from preexisting cells. (In fact, he would most likely have

9、 found Virchows addition to the cell theory of Schleiden and Schwann particularly encouraging in light of the earlier belief, debunked by Pasteurs work, that yeast cells arose by “spontaneous generation in the presence of such substrates as fermentable grape juice.)(c) In light of Virchows conclusio

10、n that cells (and therefore organisms as well, presumably) arise only from preexisting cells, he would likely have been very interested in Mendels evidence that traits such as those he observed in pea plants were heritable and could be passed from one generation to the next by transmission of “hered

11、itary factors, because the genetic continuity between generations implied by Mendels findings would have fit well with the physical continuity of generations inherent in Virchows contribution to cell theory.(d) If Miescher were sufficiently foresighted, he might have been most interested in the work

12、 of Mendel because Mieschers discovery of what we now call DNA was eventually to provide the chemical basis for the heritability of traits described by Mendel.2006.9.191. You are studying the binding of proteins to the cytoplasmic face of cultured neuroblastoma (神经母细胞瘤) cells and have found a method

13、 that gives a good yield of inside-out vesicles from the plasma membrane. Unfortunately, your preparations are contaminated with variable amounts of right-side-out vesicles. Nothing you have tried avoids this variable contamination.A friend suggests that you pass your vesicles over an affinity colum

14、n made of lectin coupled to solid beads. What is the point of your friends suggestion?回答关键词：膜糖仅存在于外膜，凝集素与糖亲和，亲和层析的方法。2. Proteins that span a membrane as an helix have a characteristic structure in the region of the bilayer. Which of the three 20-amino acid sequences listed below is the most likely c

15、andidate for such a transmembrane segment? Explain the reasons for your choice.A. ITLIYFGVMAGVIGTILLISB. ITPIYFGPMAGVIGTPLLISC. ITEIYFGRMAGVIGTDLLISAnswer: A. 跨膜蛋白需疏水。2006.9.26When present in the culture medium, ouabain (乌本苷) inhibits the Na+/K+ ATPase in cultured cells. But when the drug is microin

16、jected into cells, it exerts no inhibitory effect. Although ouabain itself possesses no negative charge ouabain treatment causes the subunits of the Na+/K+ ATPase to become more negatively charged but doesnt alter the charge properties of the subunits.a. On which side of the plasma membrane are the

17、ouabain and ATP-binding sites of the enzyme located?b. During the transport process, the Na+/K+ ATPase becomes transilently phosphorylated. What do these observations suggest about a likely mechanism for ouabain inhibition of this ion pump?c. Which of the two subunits, or, is most likely to be phosp

18、horylated?A、外侧。B、抑制去磷酸化。C、。2006.10.101. Cadherins are known to mediate homophilic interactions between cells, what is a homophilic interaction and how can this be demonstrated experimentally for E- and P- cadherins?2. Proteoglycans are characterized by the abundance of negative. Charges on their sug

19、ar groups, how would the properties of these compounds differ if the negative charges were cut as abundant?2006.10.171. Gap junctions are dynamic structures that, like conventional ion channels, are gated: they can close, by a reversible conformational change in response to changes in the cell. The

20、permeability of gap junctions decreases within seconds, for example, when the intracellular Ca2+ is raised. Speculate why this form of regulation might be important for the health of a tissue.2. Cancerous liver cells can be restored to their normal growth by inserting the gene for E-cadherin. This i

21、ndicates that cadherin is involved ina. Formation of the extracellular matrix.b. Opening voltage-gated channels.c. Activation of cAMP.d. Cell migration.e. None of the above.Answer: D.2006.10.241. Why do you suppose cells have evolved intracellular Ca2+ stores even if extracellular Ca2+ is usually no

22、t limiting?2. Hypertension or high blood pressure, is often seen in elderly people. A typical prescription to reduce a patients blood pressure uncludes compounds called -blockers, which block-adrenergic(肾上腺素能) receptors through-out the body. These receptors binds epinephrine there by activating a ce

23、llular response. Why do you think -blockers are effective in reducing blood pressure?2006.10.311. Latent gene regulatory proteins are prevented from entering the nucleus until the cell receives an appropriate signal. List four ways by which cells keep gene regulatory proteins out of the nucleus, and

24、 give an example of a latent gene regulatory protein that is controlled by each mechanism.2. Dinitrophenol (二硝基苯酚，DNP) is a small molecule that renders membranes permeable to protons. In the 1940s, small amounts of this highly toxic compound were given to patients to induce weight loss. DNP was effe

25、ctive in producing weight loss, especially loss of fat reserves. Can you explain how it might cause such loss?2006.11.71. When the antibiotic valinomycin (is added to actively respiring mitochondria, several things happen: the yeiled of ATP decreases the rate of O2 consumption increases, heat is rel

26、eased, and the pH gradient across the inner mitochondria membrane increases. Does valinomycin act as an uncoupler or an inhibitor of oxidative phosphorylation? Explain the experimental observations in terms of the antibiotics ability to transfer K+ ions across the inner mitochondria membrane.解偶联剂。2.

27、 Primary hyperoxaluria type 1 (pH1) is a lethal autosomal recessive disease, caused by a deficiency of the liver-specific peroxisomal enzyme alanine; glyoxylute (乙醛酸) amino transferase (AGT). About one-third of pH1 patients possess significant levels of AGT protein and their AGT contains two critica

28、l single amino acid changes: one that interferes with peroxisomal targeting and a second that allows the N-terminus to form an amphipathic helix with a positively charged side. Where do you suppose this mutant AGT is found in cells from these patients? Explain your reasoning.2006.11.141. To aid your

29、 studies of protein import into mitochondria , you treat yeast cells with cycloheximide (放线菌酮), which blocks ribosome movement along mRNA. When you examine these cells in the electron microscope, you are surprised to find cytosolic ribosomes attached to the outside of the mitochondria. By contast, y

30、ou have never seen attached ribosomes in the absence of cycloheximide. To investigate this phenomenon further, you prepare mitochondria from cells that have been treated with cycloheximide and then extract the mRNA that is bound to the ribosomes associated with the mitochondria. You translate this m

31、RNA in vitro and compare the protein products with similarly translated mRNA from the cytosol. The results are clear-out: the mitochondria-associated ribosomes are translating mRNAs that encode mitochondria proteins.You are astounded! Here, clearly visible in the electron micrographs, seems to be pr

32、oof that protein import into mitochondria occurs during translation. How might you reconcile this result with the prevailing view that mitochondria proteins are imported after they have been synthesized and released from ribosomes?信号肽与膜受体结合，阻断剂阻止了新生肽的释放。2006.11.211. Short answer:Give the significanc

33、e (not the definition) of the following terms or phases. Say what they do or why they are important. e.g. endoplasmic reticulum: delineates an intracellular compartment that functions in the sorting of newly synthesized protein and provides a surface for the synthesis of many proteins.(1) retrograde

34、 movement of Golgi vesicles(2) phosphorylated mannose residues or TGN glycoproteins.Answer:a、高尔基体的小泡回流运动：将包装错误的蛋白遣回；不良环境中的应激反应。b、TGN糖基化蛋白甘露糖残基的磷酸化：蛋白质分选的识别标记。2. Compare and contrast the following:(1) Synthesis of N-linked vs.O-linked oligosaccharides(2) autophagy vs. phagocytosisa、N-连接糖基化在内质网合成，高尔基体

35、加工，且连接的是Asn的酰氨基， O-连接糖基化在高尔基体合成，连接的是Ser/Thr残基。b、吞噬作用是消除外来入侵的病毒；自噬作用是清除细胞内衰老等残剩的细胞和细胞器。2006.11.28Influenza viruses are surrounded by a membrane that contains a fusion protein, which is activated by acidic pH. Upon activation, the protein causes the viral membrane to fuse with cell membranes. An old f

36、olk remedy against flu recommends that one should spend a night in a horses stable. Odd as it may sound, theres a rational explanation for this advice. Air in stables contains ammonia (NH3) generated by bacteria from the horses urine. Sketch a diagram showing the pathway (in detail) by which flu vir

37、us enters cells and speculate how NH3 may protect cells from virus infection.(Hint: NH3 can neutralize acidic solution by the reaction NH3 + H+ NH4+.)Answer:NH3可以很容易的通过细胞膜，发生反应NH3 + H+ NH4+，生成的NH4+却不容易再运出细胞膜，从而使内吞体环境的pH呈碱性，防止融合蛋白的激活。2006.12.5Your adviser is explaining his results in your weekly lab

38、meeting. By fusing his protein of interest to GFP, he has shown that it is located entirely in the nucleus. But he wonders if it is a true nucleus protein or a shutting protein that just spends most of its time in the nucleus. He is unsure how to resolve this issue. He knows that leptomycin B will n

39、ot be helpful in this instance and asks for input. Having just read an article about how a similar protein was answered, you suggest that he makes a heterocaryon by fusing cells that are expressing his tagged protein with an excess of cells that are not expressing it. You tell him that in the presen

40、ce of a protein synthesis inhibitor to block new synthesis of the tagged protein, he can resolve the issue by examining fused cells with two nucleuses. He gives you a puzzled look and asks how that helps. You tell him what he has so often told you “Think about it.”问：操作的关键是什么？答：融合后加蛋白质合成抑制剂。2006.12.1

41、21. (T/F) Deacetylation of histone tails allows nucleosomes to pack together into tighter arrays which usually reduce gene expression. Explain your answer.T组蛋白尾部去乙酰化暴露出带正电荷的碱性氨基酸残基，带正电荷的组蛋白与带负电的DNA结合更加紧密，从而使组蛋白在与转录因子的竞争中获胜，于是基因表达降低。2. A single nucleosome is 11nm long and contains 146bp of DNA (0.34n

42、m/bp). What packing ratio (DNA length to nucleosome length) has been achieved by wrapping DNA around the histone octamer? Assuming that therere an additional 54bp of extended DNA in the linker between nucleosomes. How condensed is “beads-on-a-srting” DNA relative to fully extended DNA? What fraction

43、 of 100,000-fold condensation that occurs at mitosis does this first level of packing represent?a、包装率（146bp0.34nm/bp）/11nm4.5（倍）b、浓缩倍数（14654）bp0.34nm/bp/（11nm54bp0.34nm/bp）2.3（倍）c、浓缩比2.3/100000.0232006.12.191. Vertebrate cells use several different CDKs to manage various transitions in the cell cycl

44、e, yet budding yeast is able to get by with a single CDK. How do budding yeast cells manage that neat trick?芽殖酵母有多种不同的周期蛋白，CDK与这些不同的蛋白结合发挥不同的功能。2. How could you explain each of the following experimental observations?Mutations that inactivate the main protein phosphatase used to catalyze protein dep

45、hosphorylations cause a long delay in the reconstruction of the nuclear envelope that normally takes place at the end of mitosis.蛋白磷酸酶的突变导致其失活，于是不能催化蛋白质去磷酸化，蛋白去磷酸化速率减慢，所以核膜重建延迟很多。3. (T/F) Although the length of all phases of the cycle are variable to some extent, by far the greatest variation occurs

46、 in the duration of G1. Explain your answer.T。G1期为营养生长期，由营养环境决定，多种细胞分裂所需的营养因子在此期合成； 信号调控（血清培养基：生长因子），周围细胞是否允许它生长。2006.12.261. If a cell just entering mitosis is treated with nocodazole which destabilizes microtubules, the nuclear envelope breaks down and chromosomes condense, but no spindle forms an

47、d mitosis arrests. In contrast, if such a cell is treated with cytochalosin D, which destabilizes actin filaments, mitosis proceeds normally but a bi-nucleate cell is generated and proceeds into G1. Explain the basis for the different outcomes of these treatments with cytoskeleton inhibitors. What d

48、o these results tell you about cell-cycle checkpoints in M phase?Answer:诺可唑影响微管装配，纺锤体不能形成；细胞松弛素D影响微丝收缩环形成，使胞质分裂不能进行。这些结果说明M期关卡是在核分裂时期的（因为从M到G1期，说明胞质分裂期无关卡）。2006.12.301. Assume liver and kidney tissues from the same mouse each contains about 10,000 species of cytosolic mRNA. But only 25% of these are

49、 common to the two tissues.(a) suggest an experimental approach that might be used to establish that some of the mRNA molecules are common to both tissues, but others are not.(b) one possible explanation for the data is that differential transcription occurs in liver and kidney nuclei. What is anoth

50、er possible explanation? Describe an experiment that would enable you to distinguish between these possibilities.(c) If all mRNA molecules had been shown to be common to both liver and kidney and yet the two tissues were known to be synthesizing different proteins, what level of control would you ha

51、ve to assume was operating?Ansewr: (a) 分离总RNA，反转录建立2个cDNA文库，电泳挑出探针杂交。(b) 1、可变剪接；2、运输出细胞核时产生的差错；3、RNA编辑。(c) 翻译水平。2007细胞课Q&AQQ1:An adult human is composed of about 1013 cells, all of which are derived by cell division from a single fertilized egg.A. Assuming that all cells continue to divide (like bac

52、teria in rich media). How many generations of cell divisions would be required to produce 1013 cells?B. Human cells in culture divide about once per day. Assuming all cells continue to divide at this rate during development, how long would it take to generate an adult organism?C. Why is it, do you t

53、hink, that adult human take longer to develop than calculations might suggest?Q2:Friedrich Miescher (1844-1895), Gregor Mendel (1822-1884), Louis Pasteur (1822-1895), and Rudolf Virchow (1821-1902) were European scientists (from Switzerland, Austria, France, and Germany, respectively) whose most imp

54、ortant discoveries were made in the 20-year period from 1855 to 1875. assume that the four men met at a scientific conference in 1875 to discuss their respective contributions to biology.(a) What might the four scientists have found they had in common?(b) What do you think Pasteur might have found m

55、ost intriguing or relevant about Virchows work? Explain your answer.(c) What do you think Virchow might have found most intriguing or relevant about Mendels work? Explain your answer.(d) In whose work do you think Miescher might have been the most interested? Explain your answer.Q3:Proteins that spa

56、n a membrane as an helix have a characteristic structure in the region of the bilayer. Which of the three 20-amino acid sequences listed below is the most likely candidate for such a transmembrane segment? Explain the reasons for your choice.A. ITLIYFGVMAGVIGTILLISB. ITPIYFGPMAGVIGTPLLISC. ITEIYFGRM

57、AGVIGTDLLISQ4:You are studying the binding of proteins to the cytoplasmic face of cultured neuroblastoma (神经母细胞瘤) cells and have found a method that gives a good yield of inside-out vesicles from the plasma membrane. Unfortunately, your preparations are contaminated with variable amounts of right-si

58、de-out vesicles. Nothing you have tried avoids this variable contamination.A friend suggests that you pass your vesicles over an affinity column made of lectin coupled to solid beads. What is the point of your friends suggestion?Q5:Gorter and Grendel Revisited. Gorter and Grendels classic conclusion that the plasma membrane of the human erythrocyte consists of a lipid bilayer was based on the following observations:(i) the lipids that they extracted with acetone from 4.74 109 erythrocy