生物專業(yè)英語課文中英互譯整理版

Mostofthepropertiesweassociatewithlifearepropertiesofthecytoplasm.Muchofthemassofacellconsistsofthissemifluidsubstance,whichisboundedontheoutsidebytheplasmamembrane.Organellesaresuspendedwithinit,supportedbythefilamentousnetworkofthecytoskeleton.Dissolvedinthecytoplasmicfluidarenutrients,ions,solubleproteins,andothermaterialsneededforcellfunctioning.生命的大部分特征表現(xiàn)在細胞質的特征上。細胞質大部分由半流體物質組成，并由細胞膜(原生質膜)包被。細胞器懸浮在其中，并由絲狀的細胞骨架支撐。細胞質中溶解了大量的營養(yǎng)物質，離子，可溶蛋白以及維持細胞生理需求的其它物質。(細胞核：信息中心)Theeukaryoticcellnucleusisthelargestorganelleandhousesthegeneticmaterial(DNA)onchromosomes.(Inprokaryotesthehereditarymaterialisfoundinthenucleoid.)Thenucleusalsocontainsoneortwoorganelles-thenucleoli-thatplayaroleincelldivision.Apore-perforatedsaccalledthenuclearenvelopeseparatesthenucleusanditscontentsfromthecytoplasm.Smallmoleculescanpassthroughthenuclearenvelope,butlargermoleculessuchas真核細胞的細胞核是最大的細胞器，細胞核對染色體組有保護作用(原核細胞的遺傳物質存在于擬核中)。細胞核含有一或二個核仁，核仁促進細胞分裂。核膜貫穿許多小孔，小分子可以自由通過核膜，而象mRNA和核糖體等大分子必須通過核孔運輸。Alleukaryoticcellscontainmostofthevariouskindsoforganelles,andeachorganelleperformsaspecializedfunctioninthecell.Organellesdescribedinthissectionincluderibosomes,theendoplasmicreticulum,theGolgicomplex,所有的真核細胞都含有多種細胞器，每個細胞器都有其特定功能。本節(jié)主要介紹核糖體，內質網(wǎng)，高爾基體系，液泡，溶酶體，線粒體和植物細胞中的質體。Thenumberofribosomeswithinacellmayrangefromafewhundredtomanythousands.Thisquantityreflectsthefactthat,ribosomesarethesitesatwhichaminoacidsareassembledintoproteinsforexportorforuseincellprocesses.Acompleteribosomeiscomposedofonelargerandonesmallersubunit.DuringproteinsynthesisthetwosubunitsmovealongastrandofmRNA,"reading"thegeneticsequencecodedinitandtranslatingthatsequenceintoprotein.SeveralribosomesmaybecomeattachedtoasinglemRNAstrand;suchacombinationiscalledapolysome.Mostcellularproteinsaremanufacturedonribosomesinthecytoplasm.Exportableproteinsandmembraneproteinsareusuallymadeinassociationwiththeendoplasmicret核糖體的數(shù)量變化從幾百到幾千，核糖體是氨基酸組裝成蛋白質的重要場所。完整的核糖體由大亞基和小亞基組成。核糖體沿著mRNA移動并閱讀遺傳密碼，翻譯成蛋白質。一條mRNA上可能有多個核糖體，稱多聚核糖體。大多數(shù)細胞蛋白是由細胞質中核糖體生產。輸出蛋白和膜蛋白通常與內質網(wǎng)有關。Theendoplasmicreticulum,alacyarrayofmembranoussacs,tubules,andvesicles,maybeeitherrough(RER)orsmooth(SER).Bothtypesplayrolesinthesynthesisandtransportofproteins.TheRER,whichisstuddedwith內質網(wǎng)，帶有花邊的生物囊，有管狀，泡狀之分，以及光滑和粗糙面區(qū)別。兩種都與蛋白質的合成和運輸有關。粗糙內質網(wǎng)上分布許多核糖體，也可能提供細胞分裂后所需的細胞膜。Bothtypesofendoplasmicreticulumserveascompartmentswithinthecellwherespecificproductscanbeisolatedandsubsequentlyshuntedtoparticularareasinoroutsidethecell.光滑內質網(wǎng)上無核糖體，主要作用是脂肪和類固醇的合成以及細胞內有毒物質的氧化。兩種內質網(wǎng)合成的產物在其中進行分流或運輸?shù)郊毎?。Transportvesiclesmaycarryexportablemoleculesfromtheendoplasmicreticulumtoanothermembranousorganelle, theGolgicomplex.WithintheGolgicomplexmoleculesaremodifiedandpackagedforexportoutofthecellorfordeliveryelsewhereinthecytoplasm.運輸小泡能夠將可運輸分子從內質網(wǎng)運輸?shù)礁郀柣鶑秃象w上。在高爾基復合體中修飾，包裝后輸出細胞或傳遞到細胞質中的其他場所。Vacuolesincellsappeartobehollowsacsbutareactuallyfilledwithfluidandsolublemolecules.Themostprominentinanimalcellscarryoutphagocytosis(theintakeofparticulatematter)andpinocytosis(vacuolardrinking).細胞中的液泡好象是中空的，但實際上充滿了液體和可溶分子。最典型的液泡存在于植物細胞中，儲備水，糖以及其它分子。動物中的液泡起吞噬和胞飲作用。intheGolgicomplex)thatcanbreakdownmostbiologicalmacromolecules.Theyacttodigestfoodparticlesandto溶酶體是液泡亞單位，含有消化酶，降解大部分生物大分子。消化食物微粒和降解損傷的細胞殘片。Mitochondriaarethesitesofenergy-yieldingchemicalreactionsinallcells.Inaddition,plantcellscontainplastidsthatutilizelightenergytomanufacturecarbohydratesintheprocessofphotosynthesis.ItisonthelargesurfaceareaprovidedbytheinnercristaeofmitochondriathatATP-generatingenzymesarelocated.Mitochondriaareself-replicating,andprobablytheyaretheevolutionarydescendantsofwhatwereoncefree-livingprokaryotes.線粒體是細胞中化學產能的場所。另外，植物細胞中的質體在光合作用中利用光能產生碳水化合物，線粒體內嵴上提供了很大的表面積并分布著產ATP酶。線粒體自我復制，并且可能是自由生活的原核生物在進化中形成的后andchromoplasts,whichcontainpigments.Themostimportantchromoplastsarechloroplasts-organellesthatcontainthechlorophyllusedinphotosynthesis.Theinternalstructureofchloroplastsincludesstacksofmembranescalledgranawhichareembeddedi質體有兩種類型：白色體，缺乏色素，是淀粉，蛋白質和油的儲備場所；色質體，含有色素。葉綠體是最重要的色質體，含有與光合作用有關的葉綠素。葉綠體的內部結構是由多層膜形成的葉綠體基粒，其中包埋在基質中的基粒稱子座。TheCytoskeleton(細胞骨架)Alleukaryoticcellshaveacytoskeleton,whichisaconvolutedlatticeworkoffilamentsandtubulesthatappearstofillallavailablespaceinthecellandprovidessupportforvariousotherorganelles.Alargeportionofthecytoskeletonconsistsofthreadlikemicrofilamentscomposedmainlyofthecontractileproteinactin.Theyareinvolvedinmanytypesofintracellularmovementsinplantandanimalcells.Asecondprotein,myosin,isinvolveinthecontractionofmusclecells.Anothermainstructuralcomponentofthecytoskeletonconsistsofmicrotubules,whicharecomposedoftheglobularproteintubulinandtogetheractasscaffoldingthatprovidesastablecellshape.Cytoskeletalintermediatefilamentsappeartoimparttensilestrengthtothecellcytoplasm.Mechanoenzymessuchasmyosin,dynein,andkinesininteractwiththecytoskeletalfilamentsandtubulestogenerateforcesthatcausemovements.所有的細胞都有細胞骨架，網(wǎng)絡結構的纖絲充滿了它所能觸及的全部空間并且對細胞器提供支持作用。細胞骨架大部分由微絲組成，微絲主要由可收縮的肌動蛋白組成。動植物細胞的許多種類型細胞內運動與肌動蛋白有關。第二類蛋白是肌球蛋白，它與肌肉細胞的收縮有關。細胞骨架的另一個主要結構成分是微管，由球狀的微管蛋白組成，象腳手架一般維持細胞的穩(wěn)定形態(tài)。細胞骨架的中間絲提供了細胞質伸縮動力。機械酶，例如，肌球蛋白，動力蛋白，驅動蛋白與微絲，微管相互作用產生動力而引起細胞運動。CellularMovements(細胞運動 LessonTwo 4/21photosynthesis,astheabsorbingmoleculereturnstothegroundstate,the"excess"excitationenergyistransmittedto生物分子能捕獲可見光譜中的光能。植物細胞中葉綠素在不同光波下吸收部分吸收光譜。在吸收分子中，光的作用使分子中的電子發(fā)生重排。光子的能量激活了分子的能量狀態(tài)，使其從穩(wěn)定態(tài)進入不穩(wěn)定的激活態(tài)。Allphotosyntheticorganismscontainvariousclassesofchlorophyllsandoneormorecarotenoid(accessory)pigmentsthatalsocontributetophotosynthesis.Groupsofpigmentmoleculescalledantennacomplexesarepresentonthylakoids.Lightstrikinganyoneofthepigmentmoleculesisfunneledtoaspecialchlorophyllamolecule,termedareaction-centerchlorophyll,whichdirectlyparticipatesinphotosynthesis.Mostphotosyntheticorganismspossesstwotypesofreaction-centerchlorophylls,P680andP700,eachassociatedwithanelectronacceptormoleculeandanelectrondonor.TheseaggregationsareknownrespectivelyasphotosystemI(P700)andphotosystemⅡ(P680).所有的光合作用生物含有不同等級的葉綠素和一個或多個類胡蘿卜素(光合作用的輔助色素)。稱作天線復合體的色素分子群存在于類囊體中。激活色素分子的光能進入葉綠素反應中心，其直接參與光合作用。大部分光反應細胞器擁有兩套反應中心，P680和P700,每個光系統(tǒng)都含有一個電子受體和電子供體。這些集合體就是大家熟識的光合系統(tǒng)I和光合系統(tǒng)Ⅱ。光反應：光能轉化成化學鍵能Thephotosystemsofthelight-dependentreactionsareresponsibleforthepackagingoflightenergyinthechemicalcompoundsATPandNADPH.ThispackagingtakesplacethroughaseriesofoxidationreductionreactionssetinmotionwhenlightstrikestheP680reactioncenterinphotosystemI.Inthisinitialeventwatermoleculesarecleaved,oxygenisreleased,andelectronsaredonated.Theseelectronsareacceptedfirstbyplastoquinoneandthenbyaseriesofcarriersastheydescendanelectrontransportchain.Foreachfourelectronsthatpassdownthechain,twoATPsareformed.ThelastacceptorinthechainistheP700reactioncenterofphotosystemI.Atthispointincomingphotonsboosttheenergyoftheelectrons,andtheyareacceptedbyferredoxin.Ferredoxinisthenreoxidized,andthecoenzymeNADP+isreducedtotheNADPH.TheATPgeneratedpreviouslyandtheNADPHthentakepartinthelightindependentreactions.光反應的光系統(tǒng)將光能轉化成化學復合物ATP和NADPH。當光激活光系統(tǒng)Ⅱ的光反應中心時，通過一系列的氧化還原反應實現(xiàn)能量的傳遞。反應開始時，水被分解，氧被釋放并提供電子。電子首先傳遞給質體醌，然后通過一系列載體形成的電子傳遞鏈。每傳遞4個電子，形成2個ATP。最后一個受體存在于光反應系統(tǒng)I的反應中心里。此處光子激活電子，電子傳遞給鐵氧還蛋白。鐵氧還蛋白再氧化，并且輔酶NADP+還原成NADPH。早期產生的ATP和NADPH進入暗反應。TheproductionofATPfromthetransportofelectronsexcitedbylightenergydownanelectrontransportchainistermedphotophosphorylation.Theone-wayflowofelectronsthroughphotosystemsllandIiscallednoncyclicphotophosphorylation;plantsalsoderiveadditionalATPthroughcyclicphotophosphorylation,inwhichsomeelectronsareshuntedbackthroughtheelectrontransportchainbetweenphotosystemsⅡandI.由電子傳遞鏈偶連產生ATP的過程稱為光合磷酸化。通過光合系統(tǒng)Ⅱ流經(jīng)光合系統(tǒng)I的電子路徑稱非循環(huán)式光合磷酸化；植物通過循環(huán)式光合磷酸化獲得額外的ATP,一些電子在光合系統(tǒng)I和Ⅱ之間的電子傳遞鏈中回流。TheLight-IndependentReactions:BuildingCarbohydrates暗反應：碳水化合物的形成Inthelight-independentreactionsofphotosynthesis,whicharedrivenbyATPandNADPH,C02isconvertedtocarbohydrate.ThereactionsarealsoknownastheCalvin-Bensoncycle.AtmosphericCO2,isfixedasitreactswithribulosebiphosphate(RuBP),areactionthatiscatalyzedbytheenzymeribulosebiphosphatecarboxylase.ThereductionOfC02tocarbohydrate(fructosediphosphate)iscompletedviaseveralmorestepsofthecycle.Finally,由ATP和NADPH驅動的暗反應中，二氧化碳轉化成碳水化合物。即卡爾文循環(huán)。二磷酸核酮糖固定二氧化碳，由二磷酸核酮糖羧化酶催化。(氧：光合作用的抑制因子) Highlevelsofoxygeninplantcellscandisruptphotosynthesisandcanalsocausephotorespiration-aninefficientfunofMostplantsareC3plants;theyexperiencedecreasedcarbohydrateproductionunderhot,dryconditionsasaresultoftheeffectsofphotorespiration.AmongC4plants,however,specialleafanatomyandauniquebiochemicalpathwayenabletheplanttothriveinandconditions.ThusC4plantslessenphotorespirationbycarryingoutphotosynthesisonlyincellsthatareinsulatedfromhighlevelsofCOTheyalsop大部分植物是碳3植物，在高溫干旱條件下，由于光呼吸作用而使碳水化合物的合成降低。而在大多數(shù)的碳4植物中，由于葉脈的特殊構造和獨特的化學路徑使植物依然很茂盛。這是碳固定的一個新機制。CellularReproduction:MitosisandMeiosisThecellnucleusisthemainrepositoryofgeneticinformation.WithinthenucleusarethechromosomestightlycoiledstrandsofDNAandclustersofassociatedproteins.LongstretchesofthecontinuousDNAmoleculewindaroundtheseclustersofproteins,orhistones,formingbeadlikecomplexesknownasnucleosomes.Morecoilingandproteinstomakeupthesubstancechromatin.細胞核是貯藏遺傳信息的主要場所。DNA盤繞成螺旋線以及相關的成簇蛋白質。DNA螺旋線纏繞成簇的組蛋白形成珠鏈狀的核小體。這些螺旋和超螺旋形成致密的染色體組結構。每個長鏈DNA與組蛋白和非組蛋白一起構成染色質物質。Apictorialdisplayofanorganism'schromosomesinthecoiled,condensedstateisknownasakaryotype.Karyotyperevealthatinmostcellsallbutsexchromosomesarepresentastwocopiesreferredtoashomolchromosomesarecalledautosomes.Organismswhosecellscontaintwosetsofparentalchromosomesarecalled染色體致密的超螺旋狀態(tài)我們稱染色體組。除了性染色體外，大多數(shù)細胞的染色體組成對出現(xiàn)，稱同源染色體對。非性染色體稱常染色體。生物細胞含有兩套父母本染色體的稱二倍體；含有單套染色體的稱單倍體。eachofwhichthenrepeatsthecycle.Suchcyclingineffectmakessingle-celledorganismsimmortal.Manycellsinmulticellularorganisms,includinganimalmuscleandnervecells,eitherslowthecycleorbreakoutofitaltogether.在細胞生長過程中，細胞循環(huán)遵循特定程序，分裂準備，分裂成2個子細胞，子細胞再循環(huán)。此循環(huán)使得單細胞永生。多細胞生物中的許多細胞，包括動物肌肉和神經(jīng)細胞，要么降低循環(huán)速度，要么同時分裂。Thenormalcellcycleconsistsoffourphases.ThefirstthreeincludeG1,theperiodofnormalmetabolism;Sphase,duringwhichnormalsynthesisofbiologicalmoleculescontinues,DNAisreplicated,andhistonesaresynthesized;andG2,abriefperiodofmetabolismandadditionalgrowth.TogethertheG1,S,andG2phasesarecalledinterphase.andmoveandthecelldivides.Itisbelievedthatpropertiesofthecellcytoplasmcontrolthecellcycle,alongwith正常細胞循環(huán)由4個時期組成。頭三期包括G1,正常新陳代謝；S期，正常新陳代謝同時，DNA復制，組蛋白合成；G2期，短期的新陳代謝和少許生長。G1,S,和G2稱分裂間期。最后是M期，有絲分裂期，復制的染色體組濃縮，移動并細胞分裂。據(jù)稱是染色質控制了細胞循環(huán)，伴隨外部激活因子和抑制因子如抑素。Mitosis:PartitioningtheHereditaryMaterialconsistoftwohighlycondensedchromatidsattachedtoeachotheratacentromere.Asprophaseendsandmetaphase中期begins,thecondensed濃縮的chromosomesbecomeassociatedwiththespindle紡錘體Eventuallythechromosomesbecomearrangedinaplane(calledthemetaphaseplate)atarightangletothespindle 7/21distributed.第二次核分裂開始于分裂中期，子細胞中染色體重新排列在赤道板上。著絲粒最終分離，每個姊妹染色單體分向兩極。接著胞質分裂。產生4個單倍體，父母染色體隨機分配。reproductiveorgans,andismorerapidthansexualreproduction.Amajordisadvantageoftheasexualmodeisthataeliminationofdeleteriousmutations.Italsoallows"new"geneformstoariseandspreadthroughpopulations.有絲分裂和減數(shù)分裂在傳遞遺傳信息過程中各有優(yōu)勢。體細胞的繁殖就是父母本的克隆，其優(yōu)勢是保留了父母本的成功遺傳信息，不需要特殊器官，比性復制快的多。但一個簡單災難性事件或疾病都可能摧毀一個細胞群體。性復制的優(yōu)勢是它提供了遺傳可變性和現(xiàn)存排除有害突變的機制。也可以產生新的基因并在種群中蔓延。FoundationsofGeneticsEarlyideasofinheritanceincludedHippocrates'theoryofpangenesisandAugustWeismandsgermplasmtheory.Basedonexperimentswithmice,Weismannproposedthathereditaryinformationingametestransmittedtraitstoprogeny.Bothoftheseearlyviewsincorporatedtheblendingtheory:theyheldthatheritabletraitsofthetwoparentsblend,sothatthedistinctcharacteristicsofeacharelostinoffspring.遺傳學的早期理論包括泛生說和種質理論。基于小鼠實驗，維絲曼提出遺傳信息儲存在配子中并將遺傳信息傳遞給后代。這兩個早期觀點合起來形成融合理論：子代擁有父母本混合的遺傳特征，而不完全象親代。GregorMendel,anAugustinianmonkinthemonasteryatBrunn,Austria,isknownasthe"fatherofgenetics."Havingbeenexposedtotheoriesoftheparticulatenatureofmatterwhileauniversitystudentandhavingabackgroundinmathematics,Mendelcarriedoutaseriesofcarefullyplannedexperimentsthatdemonstratedtheparticulatenatureofheredity.HisrevolutionaryideaswereneitherunderstoodnoraccepteduntilmanyyearsafterMendeldied.孟德爾，眾所周知的遺傳學之父，是一名修道士。當他還是大學生時就提出了物質的粒子屬性。孟德爾進行了一系列周密安排的實驗來證實遺傳的顆粒性。直到他去世后，他的理論才被理解和接受。Mendelstudiedgeneticsthroughplant-breedingexperimentswiththegardenpea,aplantspeciesthatisself-fertilizingandbreedstrue(eachoffspringisidenticaltotheparentinthetraitofinterest).Totesttheblendingtheory,hefocusedhisresearchonsevendistinctcharacters.Eachofthesecharacters,suchasseedcolorandplantheight,presentonlytwo,clear-cutpossibilities.Healsorecordedthetypeandnumberofallprogenyproducedfromeachpairofparentpeaplants,andfollowedtheresultsofeachcrossfortwogenerations.孟德爾通過豌豆實驗研究遺傳學，豌豆是自花授粉植物和純品系。為驗證融合理論，他的研究主要集中在7個特征上。例如，種子顏色，植株高度，這些特征只有兩個明確的可能性。他記錄了產生的每一個子代類型和數(shù)量，在雜交產生子2代。Foreachofthecharactershestudied,Mendelfoundthatonetraitwasdominantwhiletheotherwasrecessive.Inthesecondfilial(F2)generation,theratioofdominanttorecessivewas3:1.Mendeldeducedthatthisresultwaspossibleonlyifeachindividualpossessesonlytwohereditaryunits,onefromeachparent.TheunitsMendelhypothesizedaretodayknownasalleles,alternativeformsofgenes.Genesarethebasicunitsofheredity.Anorganismthatinheritsidenticalallelesforatraitfromeachparentissaidtobehomozygousforthattrait;ifdifferentallelesforatraitareinherited,theorganismisheterozygousforthattrait.Whenanorganismisheterozygousforatrait,theresulting andproperties-differsfromitsgenotype,whichmayincludebothadominantandarecessiveallele.Apictorial對于每個特征而言，要么顯形，要么隱性。在子2代中顯形與隱性比為3:1。只有在每個個體僅擁有兩個研究遺傳單元，并每個單元來自一個親代時，實驗結果才成立。此遺傳單元就是今天共識的等位基因。兩個一樣的等位基因決定一個特征，稱純合。相反，稱雜合。當生物是雜合時，它的表型由顯性基因決定。因此，生物的表型與基因型是不同的。旁納特方格可以陳列所有可能的遺傳組合。TheresultsofMendel'sexperimentsondominantandrecessiveinheritancelettoMendel'sfirstlaw:thelawofsegregation.Thislawstatesthatforagiventraitanorganisminheritsoneallelefromeachparent.Togethertheseallelesformtheallelepair.Whengametesareformedduringmeiosis,thetwoallelesbecomeseparated(halvingofchromosomenumber).TogainevidenceforhistheoryMendelperformedtestcrosses,matingplantsofunknowngenotypetoplantsthatwerehomozygousrecessiveforthetraitofinterest.Theratioofdominantphenotypes(ifany)intheprogenymakesclearwhethertheunknowngenotypeisheterozygous,homozygousdominant,orhomozygousrecessive.分離定律，生物只遺傳父母本等位基因對的一個等位基因。減數(shù)分裂期形成配子時兩個等位基因分離。為驗證此理論，他做了測交實驗，即基因型未知的植物與純合的隱性基因植物雜交。子代顯性表型可以明確測得雜合基因或純合基因的基因型。Mendel'sldeasandtheLawofindependentAssortmentMendelalsoperformeddihybridcrosses,whichenabledhimtoconsiderhowtwotraitsareinheritedrelativetooneanother.Thisworklettothelawofindependentassortment,whichstatesthattheallelesofgenesgoverningdifferentcharactersareinheritedindependently.AnapparentexceptiontoMendel'slawsisincompletedominance,aphenomenoninwhichoffspringofacrossexhibitaphenotypethatisintermediatebetweenthoseoftheparents.However,incompletedominancereflectsthefactthatbothallelesforthetraitinquestionexertaneffectonthephenotype.Theallelesthemselvesremainseparate.雙因子雜合試驗，兩個特征是如何相互影響遺傳的。試驗結果產生獨自分配定律，即等位基因獨立遺傳。特例是，不完全顯性。子代的表型是父母本的中間類型。不完全顯性說明了兩個等位基因對表型都有影響。,等位基因會繼續(xù)分離。Mendelpresentedhisideasin1866inascientificpaperpublishedbytheBrunnSocietyforNaturalHistory.Unfortunately,themeaningofhisresearchwasnotunderstoodbyotherscientistsoftheday.Hisworkwas1866年，孟德爾在自然史上發(fā)表了他的科學論文，陳訴了他的觀點。不幸的是，他的研究不被當時科學家接受。在1900年，他的著作再被發(fā)現(xiàn)利用。SoonafterMendel'sworkwasrediscovered,WalterSuttonandTheodorBoveriindependentlyproposedthatthehereditaryunitsmightbelocatedonchromosomes.ExperimentstoprovethishypothesiswerecarriedoutbyThomasHuntMorganandhisstudentsatColumbiaUniversity,inresearchonthesexchromosomesoffruitflies.Morgan'sstudieswerealsothefirstexplorationofsex-linkedtraits.Italsoledtothediscoveryin1916byCalvinBridgesofthephenomenonofnondisjunction,inwhichachromosomepairfailstosegregateduringmeiosis.孟德爾著作被再發(fā)現(xiàn)不久，WalterSutton和TheodorBoveri提出，遺傳單位可能定位在染色體組上。伴性遺傳又導致了不分離現(xiàn)象的發(fā)現(xiàn)，即在減數(shù)分裂中，染色體對不分離。ThefirstscientisttoinvestigatethequestionofhowgenesaffectphenotypewasSirArchibaldGarrod,whosestudiesofalkaptonuriaimpliedarelationshipbetweengenesandenzymes.ThirtyyearslaterBeadleandEphrussishowedarelationshipbetweenparticulargenesandbiosyntheticreactionsresponsibleforeyecolorinfruitflies.Next,inaseries ofclassicexperimentsontheefone-gene-one-enzymehypothesis-theideathateachgenecodesforaparticularenzyme.Theirworkpavedthewayforotherresearcherstoelucidatetheprecisewaysinwhichenzymesaffectcomplexmetabolicpathways.In1949,inresearchontheroleofhemoglobininsicklecellanemia,LinusPaulinghelpedrefinetheone-gene-one-enzymehypothesisintotheone-gene-one-polypeptidehypothesis.ArchibaldGarrod是第一個研究基因是如何影響表型的科學家，他對尿黑酸癥的研究揭示了基因與酶之間的關系。Beadle和Ephrussi在三十年后對果蠅眼睛顏色的研究發(fā)現(xiàn)特殊基因與相關反應的生物合成有關。接著對面包發(fā)霉粗糙脈孢菌的突變試驗得出一個基因一個酶的假說。他們的工作為其他工作者鋪平了道路，即精確地闡明了酶影響了復雜的新陳代謝途徑。在1949年，對鐮刀狀細胞貧血癥的研究對一個基因一個酶的假說進一步上升為一個基因一個多肽。Nucleiacid,originallyisolatedbyJohannMiescherin1871,wasidentifiedasaprimeconstituentofchromosomesthroughtheuseofthered-stainingmethoddevelopedbyFeulgenintheearly1900s.FrederickGriffith'sexperimentswiththeRandSstainsofpneumococcishowedthatanasyetunknownmaterialfromonesetofbacterialcouldalterthephysicaltraitsofasecondset.Inthe1940stheteamofAvery,Macleod,andMcCartyshowedthatthisunknownmaterialwasDNA.AtaboutthesametimeP.A.LevenediscoveredthatDNAcontainedfournitrogenousbases,each在1871年，核酸最初是由JohannMiescher分離成功，并由Feulgen在1900年證實核酸是染色體組最基本的組對粗糙和光滑的肺炎球菌實驗表明，不確定的某種物質可以從一組細菌轉移到另一種細菌中。在1940年，確認該物質為DNA。四個堿基和磷酸分子分別連接在糖分子上，稱核苷酸。DisagreementoverwhetherDNAcouldcarrycomplexgeneticinformationwasendedintheearly1950sbyMarthaChaseandAlfredHershey,whoseworkwithE.colishowedclearlythatDNA,andnotprotein,isthebearerofgeneticinformation.直到1950年，通過對大腸桿菌實驗發(fā)現(xiàn)，遺傳物質是DNA,而不是蛋白質。EachDNAnucleotidecontainsafive-carbonsugar,deoxyribose,attachedtooneoffourbases:adenine,guanine,cytosine,orthymine.Adenineandguaninemoleculesaredouble-ringstructurescalledpurines,whilecytosineandthyminearesingle-ringstructurescalledpyrimidines.Themoleculemadeupofabaseplusasugaristermedanucleoside.IneachmoleculeofDNAaphosphategrouplinksthefive-carbonsugarofonenucleosidetothefive-carbonsugarofthenextnucleosideinthechain.Thisphosphatebondingcreatesasugar-phosphatebackbone.每個核苷酸都含有一個五碳脫氧核糖，分別連接4個堿基，即：腺嘌呤，鳥嘌呤，胞嘧啶，胸腺嘧啶。堿基連接糖稱核苷。磷酸鍵形成磷酸骨架。Chargaff'srulesdescribethefactthat(1)theamountofadenineisequaltotheamountofthymineinDNA,withamountofcytosineequaltothatofgu(1)腺嘌呤與胸腺嘧啶，胞嘧啶與鳥嘌呤相等；(2)腺嘌呤與胸腺嘧啶，胞嘧啶與鳥嘌呤的比例隨物種不同而不同。InthelatesandearlyresearcherslookingforthestructureofDNAdrewuponChargafhaveahelicalstructureheldinhelicalstructurewithdistancebetweenthecoils,takenbyFranklinandWilkins.直到40年代末50年代初，研究者在尋求DNA結構過程中，確立了Chargaff的觀點和，Levene的組成理論以及BasedonthisinformationWatsonandCrickproposedthedoublehelixmodelofDNA-Atwistedladder-likemoleculewithtwooutersugarphosphatechainsandrungsformedbynucleotidepairs.Pairednucleotides,whichalwaysoccurasA-TorG-C,arelinkedbyhydrogenbonds.WatsonandCrickalsoproposedthatgeneticinformationisencodedby 基于這些信息，Watson和Crick提出了雙螺旋結構模型，成對的核苷酸通過氫鍵相連，遺傳信息就貯藏在堿基對中。IntheirmodelofDNAstructureandfunction,WatsonandCrickhypothesizedthatDNAreplicatesitselfby"unzipping"alongthehydrogenbondsjoiningAtoTandCtoG.Thisprocesswouldproducetwooppositehalvesthatcouldthenserveastemplatesfortheconstructionofnew,complementarystrands.Thismodelofsemiconservativereplicationconservativebecauseeachnewmoleculehasonehalfoftheformerparentmolecule-waslaterconfirmedbytheworkofDNA進行復制是以拉鏈方式自我復制，產生的兩個二分體分別為模板生成互補鏈，即半保留復制。并由Meselson和Stahl驗證。InE.coliDNAreplicationbeginswiththeformationofabubblelikestructureonthecircularchromosomethatisproducedbyreplicationforks.StudiesofbacterialDNAreplicationhaveshownthatagrowingDNAchainlengthensonlyinthe5'to3'direction(fromthe5'carbonofonesugartothe3'carbonofthenext).Theleadingstrandissynthesizedcontinuously,whilethelaggingstrandissynthesizedinshortstretchesknownasOkazakifragments.TheenzymeDNApolymeraselinksfreenucleotidesastheylineuponthetemplateformedbytheoriginalstrandoftheparentmolecule.IneukaryotesDNAreplicationfollowsthesamegeneralprinciplesasinprokarotes.OnthelongDNAmoleculesreplicationproceeds(intwodirectionsatonce)fromhundredsorthousandsofpointsoforigin.大腸桿菌復制開始時形成泡樣復制叉，鏈生長方向由5′向3'端，前導鏈連續(xù)生成，后隨鏈由岡崎片段組成，由DNA聚合酶催化。真核生物復制與原核生物復制相似，但有幾百到幾千個復制原點(原核一般只有一個復制原點)。Thestoryoflife'soriginsbeginswiththeformationoftheearth.Thesequenceofeventsthatgaverisetoourplanetbegan,inturn,withthecosmicexplosionphysicistscalltheBigBang.Thesunatthecenterofoursolarsystemcondensedfromacloudofprimordialmatterroughly5billionyearsago;theplanets,includingtheearth,condensedabout4.6billionyearsago.Theearthiscomposedofanumberoflayers:asolidcrust,asemisolidmantle,andalargelymolten(liquid)corethathasasolidcenter.BasicphysicalfeaturesofEarththatmayhavemadetheemergenceoflifepossibleincludetheplanet'ssize,temperature,composition,anddistancefromthesun.Themajorcurrenthypothesisholdsthatlifearosespontaneouslyontheearlyearthbymeansofchemicalevolutionfrom生命起源于地球的形成。大爆炸是我們行星形成的開始。太陽在50億年前生成，位于太陽系中心，行星，包括地球，在46億年前生成。地球由多層組成：堅硬的地殼，半流體的地幔，一個很大的溶解中心中存在一個堅實的中心。地球的基本特征使生命起源成為可能，包括行星的大小，溫度，組成以及離太陽的距離。當前主要假設認為，由非生命的化學物質進化過程自發(fā)產生了生命。Evidenceforprelifestagesofchemicalorganizationcomesfromlaboratoryexperimentsthattrytoduplicatethephysicalenvironmentandchemicalresourcesoftheearlyearth.Theseexperiments,includingthepioneeringworkofMillerandUrey,havesuccessfullyproducedorganicmonomersincludingaminoacids,simplesugars,andnucleicacidbases.Theprobablenextsteptowardlifewasthespontaneouslinkingofsuchmonomersintopolymerssuchasproteinoidsandnucleiacids.Currentresearchsuggeststhatlikelysitesforthispolymerizationwereclayorrocksurfaces.通過創(chuàng)造出地球早期的自然條件和化學資源條件，科學家在實驗室中已經(jīng)獲得了化學有機體生命前階段的證據(jù)。這些實驗包括米勒等早期所做工作，成功地產出了有機單體，包括氨基酸，單糖，核酸堿基。這些單體自發(fā)的連接成多聚體，如類蛋白和核酸，使進入生命狀態(tài)成為可能。這些聚合作用可能發(fā)生在泥土或巖石表面。 Researchershavefoundthatwhenenergyisavailabletoasystemtheycangeneratethreekindaggregates.TheRussianAleksandrOparinobtainedpolymer-richdroplets,calledcoacervatesfromsolutionsofpolymers.SidneyFoxgeneratedproteinoidmicrospheresfrommixturesofaminoacidsandwater.Athirdlaboratorystructureistheliposome,asphericallipidbilayerthatformsfromphospholipids.Astructuresimilartooneormoreof當一個系統(tǒng)獲得能量時，可能發(fā)生3種有機分子的聚集。從多聚物的溶液中俄國科學家獲得了富含小液滴的多聚物，即凝聚物。從氨基酸和水的混合液中Fox獲得了類蛋白微球體。實驗室第三個結構物質是脂質體，即由磷脂形成的球形脂雙層結構。FurtherstepsintheappearanceofcellsontheearthincludedthedevelopmentofRNAandDNAasbiologicalinformationmolecules.EvidencesuggeststhatRNA,whichcanformspontaneouslyunderconditionsmimickingthoseoftheearlyearth,wasthefirstinformationalmolecule.ThediscoveryofRNAribozymes-RNAthatcanactasanenzymelike