细胞生物学历年真题试卷

一．Translation：（本大题共15分，每小题1.5分）1.Luxurygenes答案：奢侈基因2.Electrontransporter答案：电子传递体3.Gapjunction答案：间隙连接4.Telomerase答案：端粒酶5.Semi-autonomousorganelle答案：半自主性细胞器6.Targetcells答案：靶细胞7.F0-F1couplingfactor答案：F0-F1偶联因子8.Primarylysosome答案：初级溶酶体9.Microtubule答案：微管10.Integrin答案：整联蛋白二．Explanation：（本大题共55分，每小题5分）1.neuralstemcell(NSC)答案：存在于成体脑组织中的一种干细胞，它可生成神经元、星形胶质细胞、少突胶质细胞。亦可转分化成血细胞和骨骼肌细胞。2.XinactivationX答案：雌性成体细胞中两条X染色体中的一条处于正常失活状态。3.cellline细胞系答案：在培养中由原代培养物产生的可无限增殖的细胞群。一般为肿瘤细胞或转化细胞形成。4.polymorphicnucleus多形核答案：哺乳动物颗粒白细胞中形状不规则的核。5.voltage-gatedionchannel电压门控通道答案：兴奋细胞质膜上的一种离子通道，对跨膜电位差的变化极为敏感，因膜电位达到一定阈值而开放。6.contractileprotein收缩蛋白答案：细胞中参与收缩过程的蛋白质，如肌动蛋白和肌球蛋白。7.cellcoat答案：又称糖萼（glycocalyx），动物细胞质膜外的一层黏多糖物质，以共价键和膜蛋白或膜脂结合形成糖蛋白或糖脂，它对膜蛋白有保护作用，并在分子识别中起重要作用8.λ-phagevectorλ-噬菌体载体：答案：由λ噬菌体DNA发展而来的DNA克隆载体9.adaptorprotein衔接器蛋白答案：在细胞内信号传递途径中，凡是在不同蛋白质间起连接作用的蛋白质的通称。10.celladhesion细胞黏附答案：动物细胞通过细胞表面的黏附分子介导细胞之间或细胞与细胞外基质之间的黏附。11.lamin核纤层蛋白答案：核纤层结构的组成成分，属于中间纤维蛋白家族；核纤层蛋白随着细胞分裂发生周期性的磷酸化与去磷酸化变化，某些核纤层蛋白在体外能够自我组装成10nm的纤维。三．Answerquestions：（本大题共30分，每小题10分）1.Whywesaythattheorganellesofendoplamicmembraneisaunitedwhole？答:从功能上看,细胞内膜结合细胞器的分布是功能越重要越靠近中央;从层次看,上游的靠内,下游的靠外。如细胞核位于细胞的中央,它是细胞中最重要的细胞器,有两层膜结构。细胞核的外膜与内质网的膜是联系在一起的,细胞核的外膜是粗面内质网的一部分。粗面内质网的功能是参与蛋白质合成,其作用仅次于细胞核,所以内质网位于细胞核的外侧。高尔基体在内质网的外侧,接受来自内质网的蛋白质和脂肪,然后对它们进行修饰和分选,它所完成的是内质网的下游工作。溶酶体是含有水解酶的囊泡,它是由高尔基体分泌而来。内体是由内吞作用产生的具有分选作用的细胞器,它能向溶酶体传递从细胞外摄取的物质,这种细胞器一般位于细胞质的外侧。另外还有线粒体、过氧化物酶体等分布在细胞的不同部位。如果是植物细胞还有叶绿体和中央大液泡,它们是按功能定位。造成内膜系统的动态特性主要是由细胞中三种不同的生化活动引起的:①蛋白质和脂的合成活动:在动物细胞中主要涉及分泌性蛋白的合成和脂的合成和加工。脂的合成在光面内质网,而分泌蛋白的合成起始于粗面内质网,完成于高尔基体。②分泌活动:③内吞活动(endocytosispathway),是分泌的相反过程,细胞将细胞外的物质吞进内体和溶酶体。2.Whatiscelldifferentiation？Pleaseintroducethemechanism.答：1.细胞分裂的不对称性：在细胞分裂时一些重要的分子被不均等地分配到两个子细胞中2.细胞间的相互作用：（1）胚胎诱导(embryonicinduction):胚胎发育过程中,一部分细胞影响相邻细胞向一定方向分化的作用.进一步更复杂的模式由细胞间相互作用产生诱导的相互作用可以在原本等同的细胞中建立起有序的差异；（2）分化抑制:分化成熟的细胞可以产生抑素,抑制相邻细胞发生同样的分化；（3）细胞数量效应；（4）细胞外基质的影响；（5）激素的作用3.染色体与细胞分化：（1）染色体结构的变化；（2）基因删除:原生动物,昆虫,甲壳动物；（3）基因扩增:果蝇多线染色体；（4）基因重排:免疫球蛋白基因(106~108种抗体)；（5）DNA的甲基化与异染色质化:胞嘧啶的甲基化使基因失活.4,基因与细胞分化无论是母体mRNA的作用还是细胞间的相互作用,其结果是启动特定基因的表达.母体基因→间隙基因→成对基因→体节极性基因→同源异形基因(homeoticgene,Hox)5.奢侈基因与管家基因生物体细胞中含有决定生长分裂和分化的全部基因信息，按其与细胞分化的关系，可将这些基因分为两大类:奢侈基因和管家基因。奢侈基因(luxurygene)：编码细胞特异性蛋白，与各种分化细胞的特定性状直接相关，这类基因对细胞自身生存无直接影响。管家基因(housekeepinggene)：这类基因的表达产物为细胞生命活动持续需要和必不少，但与细胞分化的关系不大，在细胞分化中只起协助作用。从分子层次看，细胞分化主要是奢侈基因中某种(或某些)特定基因选择性表达的结果。某些基因的选择性表达合成了执行特定功能的蛋白质，从而产生特定的分化细胞类型。3.Pleasenarratetherelationshipofoncogeneandtumer-suppressorgene.癌基因是控制细胞生长和分裂的正常基因的一种突变形式，能引起正常细胞癌变。二抑癌基因实际上是正常细胞增殖过程中的负调控因子，它编码的蛋白往往在细胞周期的检验点上起阻止周期进程的作用。如果抑癌基因突变，丧失其对细胞增殖的负调控作用，则导致细胞周期失控而过度增殖。由抑癌基因编码的蛋白能够结合到原癌基因的启动子或增强子等位点，使转录复合物不能结合到这些位点，从而不能完成转录和翻译，失去了对细胞周期的促进作用。通过癌基因和抑癌基因的协同作用，共同调控细胞的正常的增殖过程。一．Translation：（本大题共15分，每小题1.5分）1.Gatedchannel答案：门通道2.Targetcells答案：靶细胞3.Determinants答案：决定子4.EScells答案：胚胎干细胞5.Channelprotein答案：通道蛋白6.actinfilaments答案：肌动蛋白丝7.Dedifferentiation答案：脱(去)分化8.Stemcells答案：干细胞9.Molecularchaperone答案：分子伴侣10.G-protein答案：G蛋白二．Explanation：（本大题共55分，每小题5分）1.thickfilament粗（肌）丝答案：横纹肌中的肌球蛋白II丝，直径约12－14nm。2.laserscanningconfocalmicroscope答案：利用细激光束通过物镜扫描标本成像,将不同光切面的影像经计算机图象处理，获得三维影像。3.ultrastructure超微结构答案：细胞从亚显微水平到分子水平的结构的统称，亦称亚显微结构（submicroscopicstructure）。4.liposome脂质体用悬浮在水中的磷脂分子人工制备成的脂双层小膜泡。5.transdifferentiation转分化答案：(1)已分化细胞经去分化后再分化成另一种细胞的现象，如色素细胞分化成晶状体。(2)一种组织的干细胞能够分化成他种组织细胞的现象。6.dockingprotein停泊蛋白答案：内质网膜上的信号识别颗粒受体。7.thylakoid类囊体答案：叶绿体基质中由单位膜封闭形成的扁平囊。8.nuclearporecomplex核孔复合体答案：核被膜上沟通核质和细胞质的复杂隧道结构，由多种核孔蛋白构成。隧道的内、外口和中央有由核糖核蛋白组成的颗粒。核孔对进出核的物质有控制作用。9.cytoplast,cytosome胞质体答案：利用物理或化学方法，将细胞核去除后所得到的细胞部分，可以用来研究细胞核与细胞质的关系10．axonaltransport细胞器或分子沿神经细胞轴突定向的运输，可以是顺向的（从细胞体向外）或逆向的（向着细胞体11.sexdetermination性别决定答案：由于性染色体上的性别决定基因地活动，胚胎发生了雄性和雌性的性别差异。在哺乳动物中，基因型若为XY，则为雄性性，XX为雌性。三．简答题：（本大题共30分，每小题10分）1.Pleasenarratethecharacteristicsoftheagingcell.答案：1，水份减少，代谢速率减慢2，呼吸速率降低3，酶溶性下降4，色素，钙以及一些惰性物积累，不溶性废物增加5胶原弹性降低，张力增强。分子链间的2.Pleaseintroducethemaincheckpointsduringthecellcycle.答：细胞周期检验点是细胞周期调控的一种机制,主要是确保周期每一时相事件的有序、全部完成并与外界环境因素相联系。它保证前一个事件完成之后，才启动下一个事件。主要检验点包括：G1/S检验点：在酵母中称start点，在哺乳动物中称R点(restrictionpoint)，控制细胞由静止状态的G1进入DNA合成期，相关的事件包括：DNA是否损伤？细胞外环境是否适宜？细胞体积是否足够大？S期检验点：DNA复制是否完成？G2/M检验点：是决定细胞一分为二的控制点，相关的事件包括：DNA是否损伤？细胞体积是否足够大？纺锤体组装检验点：任何一个着丝点没有正确连接到纺锤体上，引起细胞周期中断。3.Whatisthebasiccharacteristicsofcancercells?1.细胞生长与分裂失去控制：癌细胞的生长与分裂失去控制，成为不死的永生细胞核质比例增大，分裂速度加快，结果破坏了正常组织的结构与功能。2.具有侵润性和扩散性：癌细胞粘着性下降，具有侵润性和扩散性，易于浸润周围的健康组织，或通过血液循环或通过淋巴途径转移并在其它部位粘着和增殖。3.细胞间相互作用改变：正常细胞通过细胞表面特异性蛋白的相互作用识别，进而形成特定的组织与器官。癌细胞冲破了细胞识别作用的束缚，异常表达某些膜受体蛋白，以便与别处细胞粘着生长。4.蛋白表达谱系或蛋白活性改变：出现一些错位表达的蛋白，具有较高的端粒酶活性，异常表达与恶性增殖、扩散等过程相关的蛋白。5.mRNA转录谱系的改变：基因表达和调控方向的改变。体外培养的恶性转化细胞的特征：人工诱导培养的恶性转化细胞同样具有无限增殖的能力，贴壁性下降，失去运动和分裂的接触抑制一．中英互译：（本大题共30分，每小条1分）1.Gatedchannel答案：门通道2.Discontinuoussecretion答案：不连续分泌3.Targetcells答案：靶细胞4.Triggerprotein答案：触发蛋白5.generaltranscriptionfactors答案：通用转录因子6.Determinants答案：决定子7.Celldifferentiation答案：细胞分化8.N-linkedoligosaccharides答案：N-连接寡糖9.Germplasm答案：生殖质10.Peroxisome答案：过氧化物酶体11.EScells答案：胚胎干细胞12.Myeloidbody答案：髓样小体13.Coatedvesicle答案：有被小泡14.Channelprotein答案：通道蛋白15.actinfilaments答案：肌动蛋白丝16.calmodulin答案：钙调蛋白（钙调素）17.Informasomes答案：信息体18.Spliceosome答案：剪接体19.Dedifferentiation答案：脱(去)分化20.Proto-oncogenes答案：原癌基因21.Dictyosome答案：分散高尔基体22.Stemcells答案：干细胞23.Molecularchaperone答案：分子伴侣24.G-protein答案：G蛋白25.Carrierprotein答案：载体蛋白(透性酶)26.Membranedifferentiation答案：膜分化27.Oncogene答案：癌基因28.Ribozyme答案：RNA催化剂(核酶)29.Alternativesplicing答案：交替剪接30.Lysosomalmembraneglycoprotein答案：溶酶体膜糖蛋白二．名词解释：（本大题共30分，每小条2分）1.thickfilament粗（肌）丝答案：横纹肌中的肌球蛋白II丝，直径约12－14nm。2.osteoclast破骨细胞答案：在生长中的骨的骨髓中形成的一种巨大的多核细胞，具有破骨功能。osteocyte骨细胞3.ultrastructure超微结构答案：细胞从亚显微水平到分子水平的结构的统称，亦称亚显微结构（submicroscopicstructure）。4.fusin引信蛋白答案：在各种CD4细胞中广泛表达的一种7次穿膜的G蛋白，与趋化因子受体相连，当HIV病毒感染T细胞时起辅因子的作用。5.glialcells胶质细胞答案：神经系统中的支持细胞，包括脊椎动物中枢神经系统中的少突胶质细胞和星形胶质细胞以及周围神经系统中的雪旺细胞。6.dockingprotein停泊蛋白答案：内质网膜上的信号识别颗粒受体。7.lamellipodium片足答案：细胞表面的外被质膜的薄片状突起，内部有肌动蛋白丝网络的支撑，与细胞运动有关。8.myofibril肌原纤维答案：由粗肌丝和细肌丝规则排列构成的肌纤维亚单位。9.cytoplast,cytosome胞质体答案：利用物理或化学方法，将细胞核去除后所得到的细胞部分，可以用来研究细胞核与细胞质的关系。10.axonaltransport轴突运输答案：细胞器或分子沿神经细胞轴突定向的运输，可以是顺向的（从细胞体向外）或逆向的（向着细胞体）。11.contractileprotein收缩蛋白答案：细胞中参与收缩过程的蛋白质，如肌动蛋白和肌球蛋白。12.Vitalstaining,intravitalstaining活体染色答案：使用毒性小的染料对活体细胞或组织的染色。13.Barrbody巴（尔）氏小体答案：雌性哺乳动物体细胞在有丝分裂间期的细胞核中染色很深、由一条失活的X染色体凝缩而成的染色质小体，又称性染色质小体(sex-chromatinbody)；1949年为M.Barr所发现。14.monoclonalantibody单克隆抗体答案：从某一杂交瘤克隆中分泌的抗体。因为每一个克隆都来自于一个B细胞，因此制备的抗体具有高度专一性。15.leucoplast白色体答案：一种无色的质体。三．简答题：（本大题共40分，每小条8分）1.细胞分化是被选定的不同特异基因表达的结果，请举例说明分化时特异基因的表达调控方式2.简述衰老细胞的特征。答案：1，水份减少，代谢速率减慢2，呼吸速率降低3，酶溶性下降4，色素，钙以及一些惰性物积累，不溶性废物增加5胶原弹性降低，张力增强。分子链间的3.高尔基体在形态结构上至少由互相联系的三个部分组成，请简述各部分的功能。答案：1，高尔基体顺面膜囊中间多孔而且连续分支状的网结构，接受来自内质网新合成的物质并将其分类后大部分转入高尔基体中间膜囊，小部分蛋白质与脂质再返回内质网；2， 高尔基体中间膜囊多为糖基化修饰、糖脂的形成以及与高尔基体有关的多糖的合成的场所；3， 高尔基体反面膜囊参与蛋白质的分类与包装最后由高尔基体输出。功能：合成糖类；将内质网合成的多种蛋白质进行加工分类包装并运送到特定部位或分泌到细胞外；蛋白质的糖基化作用和其修饰；通过蛋白酶水解作用使其成为活性肽；其它加工过程成为活性肽。4.请详述细胞质膜的分子结构及其基本特性5.核糖体各活性部位及其在蛋白质合成过程中的作用是什么？一：Giveagoodexplanationtothewordslistedbelow.1,primaryculture：Thecellsareobtaineddirectlyfromtheorganism.Mostprimaryculturesofanimalcellsareobtainedfromembryos,whosetissuesaremorereadilydissociatedintosinglecellsthanthoseofadults.Dissociationisaccomplishedwiththeaidofaproteolyticenzyme,suchastrypsin.Thetissueisthenwashedfreeoftheenzymeandusuallysuspendedinliquidmediatostartacellculture.2,liposome:Aimportantfeatureofthelipidbilayerisitsabilitytoselfassemble,forexample,asmallamountofphosphatidylcholineisdispersedinanaqueoussolution,thephospholipidmoleculesassemblespontaneouslytoformthewallsoffluid-filledsphericalvesicles,calledliposomes.3,basementmembrane:Acontinuoussheetthat(1)surroundsmuscleandfatcells,(2)underliesthebasalsurfaceofepithelialtissues,suchastheepidermisoftheskin,(3)underliestheinnerendothelialliningofbloodvessels.Basementmembranesprovidemechanicalsupportfortheattachedcells,generatesignalsthatmaintaincellsurevival,serveasasubstratumforcellmigration,separateadjacenttissueswithinanorgan,andactasabarriertothepassageofmacromolecules.4,Fibronectin:Consistsofalineararrayofdistinct“buildingblocks”thatgiveseachpolypeptideoftheextracellularmatrixamodularconstruction.Eachfibronectinpolypeptideisconstructedfromasequenceofapproximately30independentlyfoldingFnmoidules,whileFn-typemoduleswerefirstdiscoveredinfibronectin,theyarefoundaspartofmanyotherproteins,rangingfrombloodclottingfactorstomembranereceptorsandotherproteinsoftheECM.Eachofthetwopolypeptidechainsthatmakeupafibronectinmoleculecontains(1)BindingsitesforothercomponentsoftheECM,suchascollagensandproteoglycans.(2)Bindingsitesforreceptorsonthecellsurface.5,junctionalcomplex:Thecellsofcertaintissues,particularlyepitheliaandcardiacmuscle,arenotoriouslydifficulttoseparatefromoneanotherbecausetheyareheldtogethertightlybyspecializedcalcium-dependentadhesivejunctions.Therearetwomaintypesofadhesivejunctions:adherensjunctionsanddesmosomes.Inadditiontoadhesivejunctions,epithelialcellsoftencontainothertypesofcelljunctionsthatarealsolocatedtheirlateralsurfacesneartheapicallumen.Whenthesejunctionsarearrangedinaspecificarray,thisassortmentofsurfacespecializationsiscalledajunctionalcomplex.6,gapiunction:Gapjunctionsaresitesbetweenanimalcellsthatarespecializedforintercellularcommunication.Theplasmamembranesofadjacentcellscomeveryclosetooneanotherbutdonotmakedirectcontact.Instead,thecleftbetweenthecllsisspannedbyveryfinestrandsthatarecomposedentirelyofanintegralmembraneproteincalledconnexin.Eachconnexoniscomposedofsixconnexinsubunitsarrangedaroundacentralopening.Gapjunctionscanputalargenumberofcellsofatissueintointimatecytoplasmiccontact.Thishasimportantphysiologicconsequences,becauseanumberofhighlyactiveregulatorysubstances,suchascAMPandinositolphosphates,aresmallenoughtofitthroughgap-junctionchannels.Asaresult,gapjunctionshavethepotentialtointegratetheactivitiesofindividualcellsofatissueintofunctionalunit.一：Giveagoodexplanationtothewordslistedbelow.(5x8=40points)1,cellline：Normal(nonmalignant)cellscandividealimitednumberoftimes(typically50to100)beforetheyundergosenescenceanddeath.Becauseofthis,manyofthecellsthatarecommonlyusedintissueculturestudieshaveundergonegeneticmodificationsthatallowthemtobegrownindefinitely.Cellsofthistypearereferredtoasacellline.2,Laminin：Lamininsareafamilyofextracellularglycoproteinsthatconsistofthreedifferentpolypeptidechainslinkedbydisulfidebondsandorganizedfintoamoleculeresemblingacrosswiththreeshortarmsandonelongarm.Atleast15differentlamininshavebeenidentified.Likefibronectin,extracellularlamininscangreatlyinfluenceacell’spotencialformigration,growth,anddifferentiation.Forexample,lamininsplayacriticalroleinthemigrationofprimordialgermcells.Thesecellsariseintheyolksac,whichislocatedtheembryoitself,andthenmigratebywayofthebloodstreamandembryonictothedevelopinggond,wheretheyeventuallygiverisetospermoreggs.Duringtheirmigration,theprimordialgermcellstraversesurfacesthatareparticularlyrichinlaminin.Studiesindicatethattheprimordialgermcellspossessacell-surfeceproteinthatadheresstronglytooneofthesubunitsofthelamininmolecule.3,Cadherins：ThecadherinsarealargefamilyofglycoproteinsthatmediateCa2+-dependentcell-celladhesionandtransmitsignalsfromtheECMtothecytoplasm.Cadherinsjoincellsofsimilartypetooneanotheranddosopredominantlybybindingtothesamecadherinpresentonthesurfaceoftheneighboringcell.Cadherinsarefoundonthesurfacesofmanydifferentcelltypesinanimals,witheachparticularmemberofthecadherinfamilyhavingaspecificdistributionwithinthebody.4,apoptosis：isaformofprogrammedcelldeathinmulticellularorganisms.Itisoneofthemaintypesofprogrammedcelldeaths(PCD)andinvolvesaseriesofbiochemicaleventsleadingtoacharacteristiccellmorphologyanddeath,inmorespecificterms,aseriesofbiochemicaleventsthatleadtoavarietyofmorphologicalchanges,includingblebbing,changestothecellmembranesuchaslossofmembraneasymmetryandattachment,cellshrinkage,nuclearfragmentation,chromatincondensation,andchromosomalDNAfragmentation.5,extracellularmessengermolecules：Cellsusuallycommunicatewitheachotherthroughextracellularmessengermolecules.Cellsignalingisinitiatedwiththereleaseofamessengermoleculebyacellthatisengagedinsendingmessagestoothercellsinthebody.Insomecases,themessengermoleculeneedonlydiffuseacrossanarrowcleftorthroughatinybloodvesselbeforethemessagerisreceivedbyanappropriatetargetcell.Inothercases,themessengermoleculemayhavetocirculatethroughtheentirebodybeforeitreachesspecifictargetcells.Cellscanonlyrespondtoanextracellularmessageiftheyexpressreceptorsthatspecificallyrecognizeandbindthatparticularmessengermolecule.6,chromatin:ChromatinistheDNA/protein/RNAcomplexextractedfromeukaryoticlysedinterphasenuclei.Themajorproteinsinvolvedinchromatinarehistoneproteins.AndthefunctionsofchromatinaretopackageDNAintoasmallervolumetofitinthecell,tostrengthentheDNAtoallowmitosisandmeiosis,andtoserveasamechanismtocontrolexpression.Changesinchromatinstructureareaffectedmainlybymethylation(DNAandproteins)andacetylation(proteins).ChromatinstructureisalsorelevanttoDNAreplicationandDNArepair.7，house-keepinggene:Expressedinallcelltypes,essentialforallcells,responsiblefortheroutinmetabolicfunctions.8，Hayflicklimit:isthenumberoftimesacellwilldividebeforeitstopsduetothetelomerereachingacriticallength.ItwasdiscoveredbyLeonardHayflickin1965,whenHayflickdemonstratedthatnormalhumancellsinacellculturedivideabout52timesbeforeenteringasenescencephase(refutingthecontentionbyAlexisCarrelthatnormalcellsareimmortal).EachmitosisshortensthetelomereappendixontheDNAofthecell,thustickingbackan"innerclock"foreachsubsequentcopyofthecell.Thismechanismisbelievedtohaveevolvedprimarilytoprotectthebodyfromcreatingapotentially-cancerouscell.BecauseofthefragmentedwayDNAreplicates,averyshorttelomeredcellmayleadtogenomicinstabilitywhentheproteinsmeanttobelocatedonthetelomerewillfailtoattachanditwillbemarkedasadouble-strandDNAbreak,possiblyleadingtocancer.三：Answerthefollowingquestions.((10x4=40points)1,Introducethetypeandfunctionofthecytoskeleton.Thecytoskeletonisacellular"scaffolding"or"skeleton"containedwithinthecytoplasm.Thecytoskeletonispresentinallcells;Itisadynamicstructurethatmaintainscellshape,oftenprotectsthecell,enablescellularmotion(usingstructuressuchasflagella,ciliaandlamellipodia),andplaysimportantrolesinbothintracellulartransport(themovementofvesiclesandorganelles,forexample)andcellulardivision.Actinfilaments/Microfilaments:Around7nmindiameter,thisfilamentiscomposedoftwointertwinedactinchains.Microfilamentsaremostconcentratedjustbeneaththecellmembrane,andareresponsibleforresistingtensionandmaintainingcellularshape,formingcytoplasmaticprotuberances(likepseudopodiaandmicrovilli-althoughthesebydifferentmechanisms),andparticipationinsomecell-to-cellorcell-to-matrixjunctions.Inassociationwiththeselatterroles,microfilamentsareessentialtotransduction.Theyarealsoimportantforcytokinesis(specifically,formationofthecleavagefurrow)and,alongwithmyosin,muscularcontraction.Actin/Myosininteractionsalsohelpproducecytoplasmicstreaminginmostcells.Intermediatefilaments:Thesefilaments,8to12nanometersindiameter,aremorestable(stronglybound)thanactinfilaments,andheterogeneousconstituentsofthecytoskeleton.Likeactinfilaments,theyfunctioninthemaintenanceofcell-shapebybearingtension(microtubules,bycontrast,resistcompression.Itmaybeusefultothinkofmicro-andintermediatefilamentsascables,andofmicrotubulesascellularsupportbeams).Intermediatefilamentsorganizetheinternaltridimensionalstructureofthecell,anchoringorganellesandservingasstructuralcomponentsofthenuclearlaminaandsarcomeres.Theyalsoparticipateinsomecell-cellandcell-matrixjunctions.Microtubules:Microtubulesarehollowcylindersabout25nmindiameter(lumen=approximately15nmindiameter),mostcommonlycomprisedof13protofilamentswhich,inturn,arepolymersofalphaandbetatubulin.Theyhaveaverydynamicbehaviour,bindingGTPforpolymerization.Theyarecommonlyorganizedbythecentrosome.3,Introducethephasesandfeaturesofmeiosis.Meiosisisaprocessofreductiondivisioninwhichthenumberofchromosomespercelliscutinhalf.Inanimals,meiosisalwaysresultsintheformationofgametes.Unlikethesingle-celldivisionofmitosis,meiosisinvolvestwocellulardivisions:meiosisIandmeiosisII.MeiosisIMeiosisIisquitesimilartomitosis.However,thereareanumberofcrucialdifferencesbetweenmeiosisIandmitosis,allofwhichwillbeoutlinedinthediscussionofeachindividualstagebelow.InterphaseI,Justasinmitosis,thecellundergoesDNAreplicationduringthisintermediatephase.Afterreplication,thecellhasatotalof46chromosomes,eachmadeupoftwosisterchromatidsjoinedbyacentromere.ProphaseI,chromosomeslineupalongthespindleinhomologouspairs.Then,inaprocesscalledsynapsis,thehomologouspairsactuallyjointogetherandintertwine,formingatetrad(twochromosomesoftwochromatidseach,orfourtotalchromatids).OftenthisintertwiningleadsthechromatidsofhomologouschromosomestoactuallyexchangecorrespondingpiecesofDNA,aprocesscalledcrossing-overorgeneticreassortment.AfterprophaseI,themeioticcellentersmetaphaseI.Duringthisphase,thenuclearmembranebreaksdown,allowingmicrotubulesaccesstothechromosomes.Stilljoinedattheircrossoverregionsintetrads,thehomologouspairsofchromosomes,withonematernalandonepaternalchromosomeineachpair,alignatthecenterofthecellviamicrotubules,asinmitoticmetaphase.Thepairsaligninrandomorder.DuringanaphaseI,thecentromeresdonotsplit:theentirematernalchromosomeofahomologouspairispulledtooneend,andthepaternalchromosomeispulledtotheotherend.DuringtelophaseI,thechromosomesarriveatseparatepolesanddecondense.Nuclearmembranesre-formaroundthem.Thecellphysicallydivides,asinmitoticcytokinesis.ThecellsproducedbymeiosisIquicklyentermeiosisII.ThesecellsdonotundergoDNAreplicationbeforeenteringmeiosisII.DuringmeiosisII,chromosomesalignatthecenterofthecellinmetaphaseIIexactlythewaytheydoinmitoticmetaphase.InanaphaseII,thesisterchromatidsseparate,onceagaininthesamefashionasoccursinmitoticanaphase.TheonlydifferenceisthatsincetherewasnosecondroundofDNAreplication;onlyonesetofchromosomesexists.WhenthetwocellssplitattheendofmeioisisII,theresultisfourhaploidcells.4,Thetypeandcharteristicsofcelljunctions.Occludingjunctions(tightjunctions)Anchoringjunctionsa.actinfilamentattachmentsitesi.cell-celladherensjunctions(e.g.,adhesionbelts)ii.cell-matrixadherensjunctions(e.g.,focalcontacts)b.intermediatefilamentattachmentsitesi.cell-cell(desmosomes)ii.cell-matrix(hemidesmosomes)Communicatingjunctionsa.gapjunctionsb.chemicalsynapsesc.plasmodesmata(plantsonly)5,WhatarethestepsofsignaltransductionbyG-proteinCoupledreceptors?HeterotrimericGproteinsarereferredtoasGproteinsbecausetheybindguaninenucleotides,eitherGDPorGTP.Allofthemconsistofthreedifferentpolypeptidesubunits,calledα,β,andγ.Thispropertydistinguishesthemfromsmall,monomericGproteins,suchasRas.HeterotrimericGproteinsareheldattheplasmamembranebylipidchainsthatarecovalentlyattachedtotheαandγsubunits.Theguaninenucleotide-bindingsiteispresentontheGαsubunit.ReplacementofGDPbyGTP,followinginteractionwithanactivedGprotein-coupledreceptors(GPCR),resultsinaconformationalchangeintheGαsubunit.Init’sGTP-boundconformation,theGαsubunithasalowaffinityofGβ，γ，leadingtoitsdissociationfromthecomplex.EachdissociatedGαSubunit(withGTPattached)isfreetoactivateaneffectorprotein,suchasadenylylcyclase.Inthiscase,activationoftheeffectorleadstotheproductionofthesecondmessengercAMP,OthereffectorsincludephospholipaseC-βandcyclicGMPphosphodiesterase.Secondmessengers,inturn,activeoneormorecellularsignalingproteins.一：Giveagoodexplanationtothewordslistedbelow.(4x10=40points)1,primaryculture:Thecellsareobtaineddirectlyfromtheorganism.Mostprimaryculturesofanimalcellsareobtainedfromembryos,whosetissuesaremorereadilydissociatedintosinglecellsthanthoseofadults.Dissociationisaccomplishedwiththeaidofaproteolyticenzyme,suchastrypsin.Thetissueisthenwashedfreeoftheenzymeandusuallysuspendedinliquidmediatostartacellculture.2,liposome:Aimportantfeatureofthelipidbilayerisitsabilitytoselfassemble,forexample,asmallamountofphosphatidylcholineisdispersedinanaqueoussolution,thephospholipidmoleculesassemblespontaneouslytoformthewallsoffluid-filledsphericalvesicles,calledliposomes.3,celldifferentiation:Adevelopmentalprocessinwhichstructuresandfunctionsbecomeincreasinglyspecialized.4,gapiunction:Gapjunctionsaresitesbetweenanimalcellsthatarespecializedforintercellularcommunication.Theplasmamembranesofadjacentcellscomeveryclosetooneanotherbutdonotmakedirectcontact.Instead,thecleftbetweenthecllsisspannedbyveryfinestrandsthatarecomposedentirelyofanintegralmembraneproteincalledconnexin.Eachconnexoniscomposedofsixconnexinsubunitsarrangedaroundacentralopening.Gapjunctionscanputalargenumberofcellsofatissueintointimatecytoplasmiccontact.Thishasimportantphysiologicconsequences,becauseanumberofhighlyactiveregulatorysubstances,suchascAMPandinositolphosphates,aresmallenoughtofitthroughgap-junctionchannels.Asaresult,gapjunctionshavethepotentialtointegratetheactivitiesofindividualcellsofatissueintofunctionalunit.5,chromosome:ChromosomesareorganizedstructuresofDNAandproteinsthatarefoundincells.AchromosomeisasingularpieceofDNA,whichcontainsmanygenes,regulatoryelementsandothernucleotidesequences.ChromosomesalsocontainDNA-boundproteins,whichservetopackagetheDNAandcontrolitsfunctions.Ineukaryotes,nuclearchromosomesarepackagedbyproteinsintoacondensedstructurecalledchromatin.ThisallowstheverylongDNAmoleculestofitintothecellnucleus.Thestructureofchromosomesandchromatinvariesthroughthecellcycle.6,nucleosome:arethefundamentalrepeatingunitsofeukaryoticchromatin,TheyarethesmalleststructuralunitofeukaryoticDNApackaging,fundamentaltothestructureofthechromosome(s)insidethecellnucleusandcanplayaroleincontrollinggeneexpression.Theyaremadeupofabout146basepairsofDNAandfourpairsofproteinscalledhistones,andresemble"beadsonastringofDNA"whenobservedwithanelectronmicroscope(a10nmfiber).Theproteinsthatmakeupthenucleosomearecalledhistones.HistonesH2A,H2B,H3andH4formthecoreofthenucleosome,aroundwhichtheDNAiswrapped,whilehistoneH1sitsonthebaseofthenucleosomeatthejunctionbetweennucleosomeDNAandlinkerDNA,extendingalongtheDNAintothelinkerregion.7,luxurygene:Tissue-specificgenes,expressedinspecialcells,makingonecelltypedifferentfromanothercelltype.8,cellcycle:Thecellcycle,orcell-divisioncycle,istheseriesofeventsthattakeplaceinaeukaryoticcellleadingtoitsreplication.Theseeventscanbedividedintwobriefperiods:interphase—duringwhichthecellgrows,accumulatingnutrientsneededformitosisandduplicatingitsDNA—andthemitotic(M)phase,duringwhichthecellsplitsitselfintotwodistinctcells,oftencalled"daughtercells".Thecell-divisioncycleisavitalprocessbywhichasingle-celledfertilizedeggdevelopsintoamatureorganism,aswellastheprocessbywhichhair,skin,bloodcells,andsomeinternalorgansarerenewed.三：Answerthefollowingquestions.(10x4=40points)1,what’sthestructureandfunctionofsERandrER?TheendoplasmicreticulumorERisanorganellefoundinalleukaryoticcells.ERiscalledsarcoplasmicreticuluminstraitedmuscle.Itispartoftheendomembranesystem.TheERmodifiesproteins,makesmacromolecules,andtransferssubstancesthroughoutthecell.ProkaryoticorganismsdonothavemembranousorganellesandthusdonothaveanER.ThebasicstructureandcompositionoftheERissimilartotheplasmamembrane,althoughitisactuallyanextensionofthenuclearmembrane.TheERisthesiteofthetranslation,folding,andtransportofproteinsthataretobecomepartofthecellmembrane(e.g.,transmembranereceptorsandotherintegralmembraneproteins)aswellasproteinsthataretobesecretedor"exocytosed"fromthecell.PartsoftheERarecoveredwithribosomes(whichassembleaminoacidsintoproteins