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(xì)胞質(zhì)的特征上。細(xì)胞質(zhì)大部分由半流體物質(zhì)組成，并由細(xì)胞膜(原生質(zhì)膜)包被。細(xì)胞器懸浮在其中，并由絲狀的細(xì)胞骨架支撐。細(xì)胞質(zhì)中溶解了大量的營養(yǎng)物質(zhì)，離子，可溶蛋白以及維持細(xì)胞生理需求的其它物質(zhì)。(細(xì)胞核：信息中心)Theeukaryoticcellnucleusisthelargestorganelleandhousesthegeneticmaterial(DNA)onchromosomes.(Inprokaryotesthehereditarymaterialisfoundinthenucleoid.)Thenucleusalsocontainsoneortwoorganelles-thenucleoli-thatplayaroleincelldivision.Apore-perforatedsaccalledthenuclearenvelopeseparatesthenucleusanditscontentsfromthecytoplasm.Smallmoleculescanpassthroughthenuclearenvelope,butlargermoleculessuchas真核細(xì)胞的細(xì)胞核是最大的細(xì)胞器，細(xì)胞核對(duì)染色體組有保護(hù)作用(原核細(xì)胞的遺傳物質(zhì)存在于擬核中)。細(xì)胞核含有一或二個(gè)核仁，核仁促進(jìn)細(xì)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(yùn)輸。Alleukaryoticcellscontainmostofthevariouskindsoforganelles,andeachorganelleperformsaspecializedfunctioninthecell.Organellesdescribedinthissectionincluderibosomes,theendoplasmicreticulum,theGolgicomplex,所有的真核細(xì)胞都含有多種細(xì)胞器，每個(gè)細(xì)胞器都有其特定功能。本節(jié)主要介紹核糖體，內(nèi)質(zhì)網(wǎng)，高爾基體系，液泡，溶酶體，線粒體和植物細(xì)胞中的質(zhì)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(zhì)的重要場(chǎng)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(dòng)并閱讀遺傳密碼，翻譯成蛋白質(zhì)。一條mRNA上可能有多個(gè)核糖體，稱多聚核糖體。大多數(shù)細(xì)胞蛋白是由細(xì)胞質(zhì)中核糖體生產(chǎn)。輸出蛋白和膜蛋白通常與內(nèi)質(zhì)網(wǎng)有關(guān)。Theendoplasmicreticulum,alacyarrayofmembranoussacs,tubules,andvesicles,maybeeitherrough(RER)orsmooth(SER).Bothtypesplayrolesinthesynthesisandtransportofproteins.TheRER,whichisstuddedwith內(nèi)質(zhì)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(zhì)的合成和運(yùn)輸有關(guān)。粗糙內(nèi)質(zhì)網(wǎng)上分布許多核糖體，也可能提供細(xì)胞分裂后所需的細(xì)胞膜。Bothtypesofendoplasmicreticulumserveascompartmentswithinthecellwherespecificproductscanbeisolatedandsubsequentlyshuntedtoparticularareasinoroutsidethecell.光滑內(nèi)質(zhì)網(wǎng)上無核糖體，主要作用是脂肪和類固醇的合成以及細(xì)胞內(nèi)有毒物質(zhì)的氧化。兩種內(nèi)質(zhì)網(wǎng)合成的產(chǎn)物在其中進(jìn)行分流或運(yùn)輸?shù)郊?xì)胞外。Transportvesiclesmaycarryexportablemoleculesfromtheendoplasmicreticulumtoanothermembranousorganelle, theGolgicomplex.WithintheGolgicomplexmoleculesaremodifiedandpackagedforexportoutofthecellorfordeliveryelsewhereinthecytoplasm.運(yùn)輸小泡能夠?qū)⒖蛇\(yùn)輸分子從內(nèi)質(zhì)網(wǎng)運(yùn)輸?shù)礁郀柣鶑?fù)合體上。在高爾基復(fù)合體中修飾，包裝后輸出細(xì)胞或傳遞到細(xì)胞質(zhì)中的其他場(chǎng)所。Vacuolesincellsappeartobehollowsacsbutareactuallyfilledwithfluidandsolublemolecules.Themostprominentinanimalcellscarryoutphagocytosis(theintakeofparticulatematter)andpinocytosis(vacuolardrinking).細(xì)胞中的液泡好象是中空的，但實(shí)際上充滿了液體和可溶分子。最典型的液泡存在于植物細(xì)胞中，儲(chǔ)備水，糖以及其它分子。動(dòng)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(xì)胞殘片。Mitochondriaarethesitesofenergy-yieldingchemicalreactionsinallcells.Inaddition,plantcellscontainplastidsthatutilizelightenergytomanufacturecarbohydratesintheprocessofphotosynthesis.ItisonthelargesurfaceareaprovidedbytheinnercristaeofmitochondriathatATP-generatingenzymesarelocated.Mitochondriaareself-replicating,andprobablytheyaretheevolutionarydescendantsofwhatwereoncefree-livingprokaryotes.線粒體是細(xì)胞中化學(xué)產(chǎn)能的場(chǎng)所。另外，植物細(xì)胞中的質(zhì)體在光合作用中利用光能產(chǎn)生碳水化合物，線粒體內(nèi)嵴上提供了很大的表面積并分布著產(chǎn)ATP酶。線粒體自我復(fù)制，并且可能是自由生活的原核生物在進(jìn)化中形成的后andchromoplasts,whichcontainpigments.Themostimportantchromoplastsarechloroplasts-organellesthatcontainthechlorophyllusedinphotosynthesis.Theinternalstructureofchloroplastsincludesstacksofmembranescalledgranawhichareembeddedi質(zhì)體有兩種類型：白色體，缺乏色素，是淀粉，蛋白質(zhì)和油的儲(chǔ)備場(chǎng)所；色質(zhì)體，含有色素。葉綠體是最重要的色質(zhì)體，含有與光合作用有關(guān)的葉綠素。葉綠體的內(nèi)部結(jié)構(gòu)是由多層膜形成的葉綠體基粒，其中包埋在基質(zhì)中的基粒稱子座。TheCytoskeleton(細(xì)胞骨架)Alleukaryoticcellshaveacytoskeleton,whichisaconvolutedlatticeworkoffilamentsandtubulesthatappearstofillallavailablespaceinthecellandprovidessupportforvariousotherorganelles.Alargeportionofthecytoskeletonconsistsofthreadlikemicrofilamentscomposedmainlyofthecontractileproteinactin.Theyareinvolvedinmanytypesofintracellularmovementsinplantandanimalcells.Asecondprotein,myosin,isinvolveinthecontractionofmusclecells.Anothermainstructuralcomponentofthecytoskeletonconsistsofmicrotubules,whicharecomposedoftheglobularproteintubulinandtogetheractasscaffoldingthatprovidesastablecellshape.Cytoskeletalintermediatefilamentsappeartoimparttensilestrengthtothecellcytoplasm.Mechanoenzymessuchasmyosin,dynein,andkinesininteractwiththecytoskeletalfilamentsandtubulestogenerateforcesthatcausemovements.所有的細(xì)胞都有細(xì)胞骨架，網(wǎng)絡(luò)結(jié)構(gòu)的纖絲充滿了它所能觸及的全部空間并且對(duì)細(xì)胞器提供支持作用。細(xì)胞骨架大部分由微絲組成，微絲主要由可收縮的肌動(dòng)蛋白組成。動(dòng)植物細(xì)胞的許多種類型細(xì)胞內(nèi)運(yùn)動(dòng)與肌動(dòng)蛋白有關(guān)。第二類蛋白是肌球蛋白，它與肌肉細(xì)胞的收縮有關(guān)。細(xì)胞骨架的另一個(gè)主要結(jié)構(gòu)成分是微管，由球狀的微管蛋白組成，象腳手架一般維持細(xì)胞的穩(wěn)定形態(tài)。細(xì)胞骨架的中間絲提供了細(xì)胞質(zhì)伸縮動(dòng)力。機(jī)械酶，例如，肌球蛋白，動(dòng)力蛋白，驅(qū)動(dòng)蛋白與微絲，微管相互作用產(chǎn)生動(dòng)力而引起細(xì)胞運(yùn)動(dòng)。CellularMovements(細(xì)胞運(yùn)動(dòng) 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(xì)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(jìn)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(jí)的葉綠素和一個(gè)或多個(gè)類胡蘿卜素(光合作用的輔助色素)。稱作天線復(fù)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(jìn)入葉綠素反應(yīng)中心，其直接參與光合作用。大部分光反應(yīng)細(xì)胞器擁有兩套反應(yīng)中心，P680和P700,每個(gè)光系統(tǒng)都含有一個(gè)電子受體和電子供體。這些集合體就是大家熟識(shí)的光合系統(tǒng)I和光合系統(tǒng)Ⅱ。光反應(yīng)：光能轉(zhuǎn)化成化學(xué)鍵能Thephotosystemsofthelight-dependentreactionsareresponsibleforthepackagingoflightenergyinthechemicalcompoundsATPandNADPH.ThispackagingtakesplacethroughaseriesofoxidationreductionreactionssetinmotionwhenlightstrikestheP680reactioncenterinphotosystemI.Inthisinitialeventwatermoleculesarecleaved,oxygenisreleased,andelectronsaredonated.Theseelectronsareacceptedfirstbyplastoquinoneandthenbyaseriesofcarriersastheydescendanelectrontransportchain.Foreachfourelectronsthatpassdownthechain,twoATPsareformed.ThelastacceptorinthechainistheP700reactioncenterofphotosystemI.Atthispointincomingphotonsboosttheenergyoftheelectrons,andtheyareacceptedbyferredoxin.Ferredoxinisthenreoxidized,andthecoenzymeNADP+isreducedtotheNADPH.TheATPgeneratedpreviouslyandtheNADPHthentakepartinthelightindependentreactions.光反應(yīng)的光系統(tǒng)將光能轉(zhuǎn)化成化學(xué)復(fù)合物ATP和NADPH。當(dāng)光激活光系統(tǒng)Ⅱ的光反應(yīng)中心時(shí)，通過一系列的氧化還原反應(yīng)實(shí)現(xiàn)能量的傳遞。反應(yīng)開始時(shí)，水被分解，氧被釋放并提供電子。電子首先傳遞給質(zhì)體醌，然后通過一系列載體形成的電子傳遞鏈。每傳遞4個(gè)電子，形成2個(gè)ATP。最后一個(gè)受體存在于光反應(yīng)系統(tǒng)I的反應(yīng)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(chǎn)生的ATP和NADPH進(jìn)入暗反應(yīng)。TheproductionofATPfromthetransportofelectronsexcitedbylightenergydownanelectrontransportchainistermedphotophosphorylation.Theone-wayflowofelectronsthroughphotosystemsllandIiscallednoncyclicphotophosphorylation;plantsalsoderiveadditionalATPthroughcyclicphotophosphorylation,inwhichsomeelectronsareshuntedbackthroughtheelectrontransportchainbetweenphotosystemsⅡandI.由電子傳遞鏈偶連產(chǎn)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(yīng)：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(qū)動(dòng)的暗反應(yīng)中，二氧化碳轉(zhuǎn)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(gòu)造和獨(dú)特的化學(xué)路徑使植物依然很茂盛。這是碳固定的一個(gè)新機(jī)制。CellularReproduction:MitosisandMeiosisThecellnucleusisthemainrepositoryofgeneticinformation.WithinthenucleusarethechromosomestightlycoiledstrandsofDNAandclustersofassociatedproteins.LongstretchesofthecontinuousDNAmoleculewindaroundtheseclustersofproteins,orhistones,formingbeadlikecomplexesknownasnucleosomes.Morecoilingandproteinstomakeupthesubstancechromatin.細(xì)胞核是貯藏遺傳信息的主要場(chǎng)所。DNA盤繞成螺旋線以及相關(guān)的成簇蛋白質(zhì)。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(jié)構(gòu)。每個(gè)長鏈DNA與組蛋白和非組蛋白一起構(gòu)成染色質(zhì)物質(zhì)。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(xì)胞的染色體組成對(duì)出現(xiàn)，稱同源染色體對(duì)。非性染色體稱常染色體。生物細(xì)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(xì)胞生長過程中，細(xì)胞循環(huán)遵循特定程序，分裂準(zhǔn)備，分裂成2個(gè)子細(xì)胞，子細(xì)胞再循環(huán)。此循環(huán)使得單細(xì)胞永生。多細(xì)胞生物中的許多細(xì)胞，包括動(dòng)物肌肉和神經(jīng)細(xì)胞，要么降低循環(huán)速度，要么同時(shí)分裂。Thenormalcellcycleconsistsoffourphases.ThefirstthreeincludeG1,theperiodofnormalmetabolism;Sphase,duringwhichnormalsynthesisofbiologicalmoleculescontinues,DNAisreplicated,andhistonesaresynthesized;andG2,abriefperiodofmetabolismandadditionalgrowth.TogethertheG1,S,andG2phasesarecalledinterphase.andmoveandthecelldivides.Itisbelievedthatpropertiesofthecellcytoplasmcontrolthecellcycle,alongwith正常細(xì)胞循環(huán)由4個(gè)時(shí)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(shí)，DNA復(fù)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(fù)制的染色體組濃縮，移動(dòng)并細(xì)胞分裂。據(jù)稱是染色質(zhì)控制了細(xì)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(xì)胞中染色體重新排列在赤道板上。著絲粒最終分離，每個(gè)姊妹染色單體分向兩極。接著胞質(zhì)分裂。產(chǎn)生4個(gè)單倍體，父母染色體隨機(jī)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(shì)。體細(xì)胞的繁殖就是父母本的克隆，其優(yōu)勢(shì)是保留了父母本的成功遺傳信息，不需要特殊器官，比性復(fù)制快的多。但一個(gè)簡(jiǎn)單災(zāi)難性事件或疾病都可能摧毀一個(gè)細(xì)胞群體。性復(fù)制的優(yōu)勢(shì)是它提供了遺傳可變性和現(xiàn)存排除有害突變的機(jī)制。也可以產(chǎn)生新的基因并在種群中蔓延。FoundationsofGeneticsEarlyideasofinheritanceincludedHippocrates'theoryofpangenesisandAugustWeismandsgermplasmtheory.Basedonexperimentswithmice,Weismannproposedthathereditaryinformationingametestransmittedtraitstoprogeny.Bothoftheseearlyviewsincorporatedtheblendingtheory:theyheldthatheritabletraitsofthetwoparentsblend,sothatthedistinctcharacteristicsofeacharelostinoffspring.遺傳學(xué)的早期理論包括泛生說和種質(zhì)理論?；谛∈髮?shí)驗(yàn)，維絲曼提出遺傳信息儲(chǔ)存在配子中并將遺傳信息傳遞給后代。這兩個(gè)早期觀點(diǎn)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(xué)之父，是一名修道士。當(dāng)他還是大學(xué)生時(shí)就提出了物質(zhì)的粒子屬性。孟德爾進(jìn)行了一系列周密安排的實(shí)驗(yàn)來證實(shí)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(shí)驗(yàn)研究遺傳學(xué)，豌豆是自花授粉植物和純品系。為驗(yàn)證融合理論，他的研究主要集中在7個(gè)特征上。例如，種子顏色，植株高度，這些特征只有兩個(gè)明確的可能性。他記錄了產(chǎn)生的每一個(gè)子代類型和數(shù)量，在雜交產(chǎn)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(duì)于每個(gè)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(gè)個(gè)體僅擁有兩個(gè)研究遺傳單元，并每個(gè)單元來自一個(gè)親代時(shí)，實(shí)驗(yàn)結(jié)果才成立。此遺傳單元就是今天共識(shí)的等位基因。兩個(gè)一樣的等位基因決定一個(gè)特征，稱純合。相反，稱雜合。當(dāng)生物是雜合時(shí)，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?qū)Φ囊粋€(gè)等位基因。減數(shù)分裂期形成配子時(shí)兩個(gè)等位基因分離。為驗(yàn)證此理論，他做了測(cè)交實(shí)驗(yàn)，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(cè)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(yàn)，兩個(gè)特征是如何相互影響遺傳的。試驗(yàn)結(jié)果產(chǎn)生獨(dú)自分配定律，即等位基因獨(dú)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(gè)等位基因?qū)Ρ硇投加杏绊憽?等位基因會(huì)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(xué)論文，陳訴了他的觀點(diǎn)。不幸的是，他的研究不被當(dāng)時(shí)科學(xué)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(dǎo)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(duì)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(gè)研究基因是如何影響表型的科學(xué)家，他對(duì)尿黑酸癥的研究揭示了基因與酶之間的關(guān)系。Beadle和Ephrussi在三十年后對(duì)果蠅眼睛顏色的研究發(fā)現(xiàn)特殊基因與相關(guān)反應(yīng)的生物合成有關(guān)。接著對(duì)面包發(fā)霉粗糙脈孢菌的突變?cè)囼?yàn)得出一個(gè)基因一個(gè)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(fù)雜的新陳代謝途徑。在1949年，對(duì)鐮刀狀細(xì)胞貧血癥的研究對(duì)一個(gè)基因一個(gè)酶的假說進(jìn)一步上升為一個(gè)基因一個(gè)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(shí)核酸是染色體組最基本的組對(duì)粗糙和光滑的肺炎球菌實(shí)驗(yàn)表明，不確定的某種物質(zhì)可以從一組細(xì)菌轉(zhuǎn)移到另一種細(xì)菌中。在1940年，確認(rèn)該物質(zhì)為DNA。四個(gè)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(duì)大腸桿菌實(shí)驗(yàn)發(fā)現(xiàn)，遺傳物質(zhì)是DNA,而不是蛋白質(zhì)。EachDNAnucleotidecontainsafive-carbonsugar,deoxyribose,attachedtooneoffourbases:adenine,guanine,cytosine,orthymine.Adenineandguaninemoleculesaredouble-ringstructurescalledpurines,whilecytosineandthyminearesingle-ringstructurescalledpyrimidines.Themoleculemadeupofabaseplusasugaristermedanucleoside.IneachmoleculeofDNAaphosphategrouplinksthefive-carbonsugarofonenucleosidetothefive-carbonsugarofthenextnucleosideinthechain.Thisphosphatebondingcreatesasugar-phosphatebackbone.每個(gè)核苷酸都含有一個(gè)五碳脫氧核糖，分別連接4個(gè)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(jié)構(gòu)過程中，確立了Chargaff的觀點(diǎn)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(jié)構(gòu)模型，成對(duì)的核苷酸通過氫鍵相連，遺傳信息就貯藏在堿基對(duì)中。IntheirmodelofDNAstructureandfunction,WatsonandCrickhypothesizedthatDNAreplicatesitselfby"unzipping"alongthehydrogenbondsjoiningAtoTandCtoG.Thisprocesswouldproducetwooppositehalvesthatcouldthenserveastemplatesfortheconstructionofnew,complementarystrands.Thismodelofsemiconservativereplicationconservativebecauseeachnewmoleculehasonehalfoftheformerparentmolecule-waslaterconfirmedbytheworkofDNA進(jìn)行復(fù)制是以拉鏈方式自我復(fù)制，產(chǎn)生的兩個(gè)二分體分別為模板生成互補(bǔ)鏈，即半保留復(fù)制。并由Meselson和Stahl驗(yàn)證。InE.coliDNAreplicationbeginswiththeformationofabubblelikestructureonthecircularchromosomethatisproducedbyreplicationforks.StudiesofbacterialDNAreplicationhaveshownthatagrowingDNAchainlengthensonlyinthe5'to3'direction(fromthe5'carbonofonesugartothe3'carbonofthenext).Theleadingstrandissynthesizedcontinuously,whilethelaggingstrandissynthesizedinshortstretchesknownasOkazakifragments.TheenzymeDNApolymeraselinksfreenucleotidesastheylineuponthetemplateformedbytheoriginalstrandoftheparentmolecule.IneukaryotesDNAreplicationfollowsthesamegeneralprinciplesasinprokarotes.OnthelongDNAmoleculesreplicationproceeds(intwodirectionsatonce)fromhundredsorthousandsofpointsoforigin.大腸桿菌復(fù)制開始時(shí)形成泡樣復(fù)制叉，鏈生長方向由5′向3'端，前導(dǎo)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(fù)制與原核生物復(fù)制相似，但有幾百到幾千個(gè)復(fù)制原點(diǎn)(原核一般只有一個(gè)復(fù)制原點(diǎn))。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(jiān)硬的地殼，半流體的地幔，一個(gè)很大的溶解中心中存在一個(gè)堅(jiān)實(shí)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(dāng)前主要假設(shè)認(rèn)為，由非生命的化學(xué)物質(zhì)進(jìn)化過程自發(fā)產(chǎn)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(xué)資源條件，科學(xué)家在實(shí)驗(yàn)室中已經(jīng)獲得了化學(xué)有機(jī)體生命前階段的證據(jù)。這些實(shí)驗(yàn)包括米勒等早期所做工作，成功地產(chǎn)出了有機(jī)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(jìn)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(dāng)一個(gè)系統(tǒng)獲得能量時(shí)，可能發(fā)生3種有機(jī)分子的聚集。從多聚物的溶液中俄國科學(xué)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(shí)驗(yàn)室第三個(gè)結(jié)構(gòu)物質(zhì)是脂質(zhì)體，即由磷脂形成的球形脂雙層結(jié)構(gòu)。FurtherstepsintheappearanceofcellsontheearthincludedthedevelopmentofRNAandDNAasbiologicalinformationmolecules.EvidencesuggeststhatRNA,whichcanformspontaneouslyunderconditionsmimickingthoseoftheearlyearth,wasthefirstinformationalmolecule.ThediscoveryofRNAribozymes-RNAthatcanactasanenzymelike