细胞生物学英文试卷(I)

《细胞生物学英文试卷(I)》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、细胞生物学双语教案4（细胞核结构与功能）StructureandFunctionoftheNucleolusThenucleolusisorganizedfromthe"nucleolarorganizingregions"ondifferentchromosomes.AnumberofchromosomesgettogetherandtranscriberibosomalRNAatthissite.Thenuclearorganizing(NO)regionsareseenascircularareas(pale)surroundedbyarimofelectrondensefilam

2、ents.Thesefilamentscollectivelyarecalledtheparsfibrosa(PF).ThisisformedfromnewlytranscribedribosomalRNA.Thisdiagramshowsthepartsofthenucleolus.AftertheribosomalRNAistranscribed,itislinkedtoproteinsandonecanseeaccumulationofribonucleoproteinparticlesintheparsgranulosa(PG).Theseparticlesformthetwot

3、ypesofribosomalsubunits(largeandsmall)whicharethentransportedoutoftheNuclearPoresseparately.Theporesdonotaccommodatetheassembledribosomes,therefore,theycannotreenter.ThismeansthattranslationofRNAandsynthesisofproteinsmustoccuroutsidethenucleolus.FormoreinformationfollowthelinktoribosomesAfterther

4、ibosomalsubunitsareinthecytoplasm,theyareconnectedandthen,theymayattachtoendoplasmicreticulum.Theyprovideanattachmentand"codereading"siteforthemessengerRNA.Iftheyattachtoroughendoplasmicreticulum,theyformaporethatmovesthenewlysynthesizedproteinsintothecisternaoftheroughendoplasmicreticulum.Theabo

5、vefigureshowsanotherelectronmicrographofanucleoluswiththe7nuclearorganizingregion,theparsfibrosaandtheparsgranulosa.Nucleoliincreaseinnumberandenlargewhenthecellisstimulatedtoproduceproteins.Thisisasignthatthecellhasbeenstimulatedorisactivelyinvolvedinproteinsynthesis.Nucleolidisappearduringcelld

6、ivisionandthenreformatthechromosomalnucleolarorganizingcenters.OnecanstudysynthesisofribosomalRNAwiththeelectronmicroscope.Apreparationofnucleoliisdissociatedandspreadonaliquidsurface(inamannersimilartothespreadingofchromatin).Then,thesynthesisofribosomalRNAisstimulatedandafteraperiodoftime,theDN

7、AfromthenucleolarorganizingregionbeginstolooklikeaChristmastree.Thetopofthetreeisthestartsite.Asyoumovedownthe"tree",thebranchesappearlonger.EachbranchisagrowingstrandofribosomalRNA.TheDNAcodeisbeingtranscribedandthenu