生物專業(yè)英語翻譯和單詞（專業(yè)版）

生物專業(yè)英語

第一課

Cytoplasm:TheDynamic,MobileFactory

細胞質：動力工廠

Mostofthepropertiesweassociatewithlifearepropertiesofthecytoplasm.Much

ofthemassofacellconsistsofthissemifluidsubstance,whichisboundedonthe

outsidebytheplasmamembrane.Organellesaresuspendedwithinit,supportedby

thefilamentousnetworkofthecytoskeleton.Dissolvedinthecytoplasmicfluidare

nutrients,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。

TheNucleus:InformationCentral（細胞核:信息中心）

Theeukaryoticcellnucleusisthelargestorganelleandhousesthegeneticmaterial

（DNA）onchromosomes.（Inprokaryotesthehereditarymaterialisfoundinthe

nucleoid.）Thenucleusalsocontainsoneortwoorganelles-thenucleoli-thatplayarole

incelldivision.Apore-perforatedsaccalledthenuclearenvelopeseparatesthe

nucleusanditscontentsfromthecytoplasm.Smallmoleculescanpassthroughthe

nuclearenvelope,butlargermoleculessuchasmRNAandribosomesmustenterand

exitviathepores.

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。

Organelles:SpecializedWorkUnits（細胞器：特殊的功能單位）

Alleukaryoticcellscontainmostofthevariouskindsoforganelles,andeachorganelle

performsaspecializedfunctioninthecell.Organellesdescribedinthissectioninclude

ribosomes,theendoplasmicreticulum,theGolgicomplex,vacuoles,lysosomes,

mitochondria,andtheplastidsofplantcells.

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。

Thenumberofribosomeswithinacellmayrangefromafewhundredtomany

thousands.Thisquantityreflectsthefactthat,ribosomesarethesitesatwhichamino

acidsareassembledintoproteinsforexportorforuseincellprocesses.Acomplete

ribosomeiscomposedofonelargerandonesmallersubunit.Duringproteinsynthesis

thetwosubunitsmovealongastrandofmRNA,"reading"thegeneticsequencecoded

initandtranslatingthatsequenceintoprotein.Severalribosomesmaybecome

attachedtoasinglemRNAstrand;suchacombinationiscalledapolysome.Most

cellularproteinsaremanufacturedonribosomesinthecytoplasm.Exportable

proteinsandmembraneproteinsareusuallymadeinassociationwiththe

endoplasmicreticulum.

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(chǎn)。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).Bothtypesplayrolesinthesynthesisand

transportofproteins.TheRER,whichisstuddedwithpolysomes,alsoseemstobe

thesourceofthenuclearenvelopeafteracelldivides.

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。

SERlackspolysomes;itisactiveinthesynthesisoffatsandsteroidsandinthe

oxidationoftoxicsubstancesinthecell.Bothtypesofendoplasmicreticulumserve

ascompartmentswithinthecellwherespecificproductscanbeisolatedand

subsequentlyshuntedtoparticularareasinoroutsidethecell.

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(chǎn)物在其中進行分流或運輸?shù)郊毎狻?/p>

Transportvesiclesmaycarryexportablemoleculesfromtheendoplasmicreticulumto

anothermembranousorganelle,theGolgicomplex.WithintheGolgicomplex

moleculesaremodifiedandpackagedforexportoutofthecellorfordeliveryelse

whereinthecytoplasm.

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。

Vacuolesincellsappeartobehollowsacsbutareactuallyfilledwithfluidandsoluble

molecules.Themostprominentvacuolesappearinplantcellsandserveaswater

reservoirsandstoragesitesforsugarsandothermolecules.Vacuolesinanimalcells

carryoutphagocytosis(theintakeofparticulatematter)andpinocytosis(vacuolar

drinking).

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。

Asubsetofvacuolesaretheorganellesknownaslysosomes,whichcontaindigestive

enzymes(packagedinlysosomesintheGolgicomplex)thatcanbreakdownmost

biologicalmacromolecules.Theyacttodigestfoodparticlesandtodegradedamaged

cellparts.

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.In

addition,plantcellscontainplastidsthatutilizelightenergytomanufacture

carbohydratesintheprocessofphotosynthesis.Itisonthelargesurfacearea

providedbytheinnercristaeofmitochondriathatATP-generatingenzymesare

located.Mitochondriaareself-replicating,andprobablytheyaretheevolutionary

descendantsofwhatwereoncefree-livingprokaryotes.

線粒體是細胞中化學產(chǎn)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(chǎn)生碳水化合物，線粒體內崎上提供了很大的表面積并分布著產(chǎn)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代。

Therearetwotypesofplastids:leucoplasts,whichlackpigmentsandserveasstorage

sitesforstarch,proteins,andoils;andchromoplasts,whichcontainpigments.The

mostimportantchromoplastsarechloroplasts-organellesthatcontainthechlorophyll

usedinphotosynthesis.Theinternalstructureofchloroplastsincludesstacksof

membranescalledgrana,whichareembeddedinamatrixcalledthestroma.

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,whichisaconvolutedlatticeworkoffilaments

andtubulesthatappearstofillallavailablespaceinthecellandprovidessupportfor

variousotherorganelles.Alargeportionofthecytoskeletonconsistsofthreadlike

microfilamentscomposedmainlyofthecontractileproteinactin.Theyareinvolved

inmanytypesofintracellularmovementsinplantandanimalcells.Asecondprotein,

myosin,isinvolveinthecontractionofmusclecells.Anothermainstructural

componentofthecytoskeletonconsistsofmicrotubules,whicharecomposedofthe

globularproteintubulinandtogetheractasscaffoldingthatprovidesastablecell

shape.Cytoskeletalintermediatefilamentsappeartoimparttensilestrengthtothe

cellcytoplasm.Mechanoenzymessuchasmyosin,dynein,andkinesininteractwith

thecytoskeletalfilamentsandtubulestogenerateforcesthatcausemovements.

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(chǎn)生動力而引起細胞運動。

CellularMovements（細胞運動）

Althoughthecytoskeletonprovidessomestabilitytocells,itsmicrotubulesand

filamentsandtheirassociatedproteinsenablecellstomovebycreepingor

gliding.Suchmovementsrequireasolidsubstratetowhichthecellcanadhereand

canbeguidedbythegeometryofthesurface.Somecellsalsoexhibitchemotaxis,the

abilitytomovetowardorawayfromthesourceofadiffusingchemical.

盡管細胞骨架提供了細胞的某些穩(wěn)定性，微絲，微管及相關蛋白能使細胞爬行

或滑動。這種運動需要固體基質依托并通過表面幾何形狀的改變而運動。某些

細胞具備趨藥性，即趨向或逃離擴散開的化學源。

Certaineukaryoticcellscanswimfreelyinliquidenvironments,propelledbywhiplike

ciliaorflagella.Bothciliaandflagellahavethesameinternalstructure:ninedoublets

（pairsofmicrotubules）arearrangedinaringandextendthelengthoftheciliumor

flagellum,andtwomoremicrotubulesrundownthecenterofthering.Everycilium

orflagellumgrowsonlyfromthecellsurfacewhereabasalbodyislocated.Movement

isbasedontheactivitiesoftinydyneinsidearmsthatextendfromoneofthe

microtubulesofeachdoublet.

某些真核細胞能在液體液體中自由運動，由纖毛或鞭毛推動。纖毛和鞭毛具有

同樣的內部結構：九個雙微管環(huán)形排列，縱向延伸，環(huán)中心是兩個或以上微管

組成。纖毛或鞭毛從細胞表面的基體出生長，雙微管的動力蛋白臂從一側延伸

到另一側而引起運動。

Nutrients,proteins,andothermaterialswithinmostplantcellsaremovedabout

viacytoplasmicstreaming.Theprocessoccursasmyosinproteinsattachedto

organellespushagainstmicrofilamentsarrayedthroughoutthecell.Microfilaments

andmicrotubulesareresponsibleforalmostallmajorcytoplasmicmovements.During

celldivision,microtubulesofthespindleassembledfromtubutinsubunitsnear

organellescalledcentriolesmovethechromosomes.

大部分植物細胞的營養(yǎng)，蛋白質和其它物質由細胞質流運輸。這個過程是由于

依附在細胞器上的肌球蛋白反推排列在細胞周圍的微絲形成的。絕大部分細胞

質運動由微絲和微管完成。在細胞分裂期間，中心粒周圍的由微管蛋白亞基裝

配形成的紡錘體微管移向染色體。

第二課

Photosynthesisoccursonlyinthechlorophyll-containingcellsofgreenplants,algae,

andcertainprotistsandbacteria.Overall,itisaprocessthatconvertslightenergyinto

chemicalenergythatisstoredinthemolecularbonds.Fromthepointofviewof

chemistryandenergetics,itistheoppositeofcellularrespiration.Whereascellular

respirationishighlyexergonicandreleasesenergy,photosynthesisrequiresenergy

andishighlyendergonic.

光合作用只發(fā)生在含有葉綠素的綠色植物細胞，海藻，某些原生動物和細菌之

中。總體來說，這是一個將光能轉化成化學能，并將能量貯存在分子鍵中，從

化學和動能學角度來看，它是細胞呼吸作用的對立面。細胞呼吸作用是高度放

能的，光合作用是需要能量并高吸能的過程。

PhotosynthesisstartswithC02andH20asrawmaterialsandproceedsthroughtwo

setsofpartialreactions.Inthefirstset,calledthelight-dependentreactions,water

moleculesaresplit(oxidized),02isreleased,andATPandNADPHareformed.These

reactionsmusttakeplaceinthepresenceoflightenergy.Inthesecondset,called

light-independentreactions,CO2isreduced(viatheadditionofHatoms)to

carbohydrate.ThesechemicaleventsrelyontheelectroncarrierNADPHandATP

generatedbythefirstsetofreactions.

光合作用以二氧化碳和水為原材料并經(jīng)歷兩步化學反應。第一步，稱光反應，

水分子分解，氧分子釋放，ATP和NADPH形成。此反應需要光能的存在。第二

步，稱暗反應，二氧化碳被還原成碳水化合物，這步反應依賴電子載體NADPH

以及第一步反應產(chǎn)生的ATP。

Bothsetsofreactionstakeplaceinchloroplasts.Mostoftheenzymesandpigments

forthelightdependentreactionsareembeddedinthethylakoidmembraneof

chloroplasts.Thedarkreactionstakeplaceinthestroma.

兩步反應都發(fā)生在葉綠體中。光反應需要的大部分酶和色素包埋在葉綠體的類

囊體膜上。暗反應發(fā)生在基質中。

HowLightEnergyReachesPhotosyntheticCells(光合細胞如何吸收光能的)

Theenergyinlightphotonsinthevisiblepartofthespectrumcanbecapturedby

biologicalmoleculestodoconstructivework.Thepigmentchlorophyllinplantcells

absorbsphotonswithinaparticularabsorptionspectrumsstatementoftheamount

oflightabsorbedbychlorophyllatdifferentwavelengths.Whenlightisabsorbedit

altersthearrangementofelectronsintheabsorbingmolecule.Theaddedenergyof

thephotonbooststheenergyconditionofthemoleculefromastablestatetoaless-

stableexcitedstate.Duringthelight-dependentreactionsofphotosynthesis,asthe

absorbingmoleculereturnstothegroundstate,the"excess"excitationenergyis

transmittedtoothermoleculesandstoredaschemicalenergy.

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)。

Allphotosyntheticorganismscontainvariousclassesofchlorophyllsandoneormore

carotenoid(accessory)pigmentsthatalsocontributetophotosynthesis.Groupsof

pigmentmoleculescalledantennacomplexesarepresentonthylakoids.Lightstriking

anyoneofthepigmentmoleculesisfunneledtoaspecialchlorophyllamolecule,

termedareaction-centerchlorophyll,whichdirectlyparticipatesin

photosynthesis.Mostphotosyntheticorganismspossesstwotypesofreaction-center

chlorophylls,P680andP700,eachassociatedwithanelectronacceptormoleculeand

anelectrondonor.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。

TheLight-DependentReaction:ConvertingSolarEnergyintoChemical-BondEnergy

光反應：光能轉化成化學鍵能

Thephotosystemsofthelight-dependentreactionsareresponsibleforthepackaging

oflightenergyinthechemicalcompoundsATPandNADPH.Thispackagingtakes

placethroughaseriesofoxidationreductionreactionssetinmotionwhenlightstrikes

theP680reactioncenterinphotosystemII.Inthisinitialeventwatermoleculesare

cleaved,oxygenisreleased,andelectronsaredonated.Theseelectronsareaccepted

firstbyplastoquinoneandthenbyaseriesofcarriersastheydescendanelectron

transportchain.Foreachfourelectronsthatpassdownthechain,twoATPsare

formed.ThelastacceptorinthechainistheP700reactioncenterofphotosystemI.

Atthispointincomingphotonsboosttheenergyoftheelectrons,andtheyare

acceptedbyferredoxin.Ferredoxinisthenreoxidized,andthecoenzymeNADP+is

reducedtotheNADPH.TheATPgeneratedpreviouslyandtheNADPHthentakepart

inthelightindependentreactions.

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醍，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(chǎn)生的ATP和NADPH進入

暗反應。

TheproductionofATPfromthetransportofelectronsexcitedbylightenergydown

anelectrontransportchainistermedphotophosphorylation.Theone-wayflowof

electronsthroughphotosystemsIIandIiscallednoncyclicphotophosphorylation;

plantsalsoderiveadditionalATPthroughcyclicphotophosphorylation,inwhichsome

electronsareshuntedbackthroughtheelectrontransportchainbetween

photosystemsIIandI.

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：碳水化合物的形成

Inthelight-independentreactionsofphotosynthesis,whicharedrivenbyATPand

NADPH,C02isconvertedtocarbohydrate.ThereactionsarealsoknownastheCalvin-

Bensoncycle.AtmosphericC02,isfixedasitreactswithribulosebiphosphate(RuBP),

areactionthatiscatalyzedbytheenzymeribulosebiphosphatecarboxylase.The

reductionOfC02tocarbohydrate(fructosediphosphate)iscompletedviaseveral

morestepsofthecycle.Finally,RUBPisregeneratedsothatthecyclemaycontinue.

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，由二磷酸核酮糖羚化酶催化。

Oxygen:AnInhibitorofphotosynthesis(氧：光合作用的抑制因子)

Highlevelsofoxygeninplantcellscandisruptphotosynthesisandcanalsocause

photorespiration-aninefficientfunofthedarkreactionsinwhich02isfixedrather

thanC02andnocarbohydrateisproduced.

ReprievefromPhotorespiration:TheC4Pathway

MostplantsareC3plants;theyexperiencedecreasedcarbohydrateproductionunder

hot,dryconditionsasaresultoftheeffectsofphotorespiration.AmongC4plants,

however,specialleafanatomyandauniquebiochemicalpathwayenabletheplantto

thriveinandconditions.ThusC4plantslessenphotorespirationbycarryingout

photosynthesisonlyincellsthatareinsulatedfromhighlevelsofCO2.Theyalso

possessanovelmechanismforcarbonfixation.

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。

第三課

TheNucleusandChromosomes

Thecellnucleusisthemainrepositoryofgeneticinformation.Withinthenucleusarethe

chromosomestightlycoiledstrandsofDNAandclustersofassociatedproteins.Longstretchesofthe

continuousDNAmoleculewindaroundtheseclustersofproteins,orhistones,formingbeadlike

complexesknownasnucleosomes.Morecoilingandsupercoilingproducesadensechromosome

structure.EachlongstrandofDNAcombineswithhistonesandnonhistoneproteinstomakeupthe

substancechromatin.

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,condensedstateisknownasa

karyotype.Karyotyperevealthatinmostcellsallbutsexchromosomesarepresentastwocopies,

referredtoashomologouspairs.Non-sexchromosomesarecalledautosomes.Organismswhosecells

containtwosetsofparentalchromosomesarecalleddiploid;thosewithcellscontainingasinglesetof

parentalchromosomesarecalledhaploid.

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。

TheCellCycle

Thecellcycleisaregularsequenceinwhichthecellgrows,preparesfordivision,anddividestoform

twodaughtercells,eachofwhichthenrepeatsthecycle.Suchcyclingineffectmakessingle-celled

organismsimmortal.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.ThefirstthreeincludeGl,theperiodofnormal

metabolism;Sphase,duringwhichnormalsynthesisofbiologicalmoleculescontinues,DNAis

replicated,andhistonesaresynthesized;andG2,abriefperiodofmetabolismandadditional

growth.TogethertheGl,S,andG2phasesarecalledinterphase.Thefourthphaseofthecellcycleis

Mphase,theperiodofmitosis,duringwhichthereplicatedchromosomescondenseandmoveandthe

celldivides.Itisbelievedthatpropertiesofthecellcytoplasmcontrolthecellcycle,alongwithexternal

stimulatorsandinhibitorssuchaschalones.

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:PartitioningtheHereditaryMaterial

Biologistsdividethemitoticcycleintofourphases.Atthebeginningofprophasethechromosomes

eachconsistoftwohighlycondensedchromatidsattachedtoeachotheratacentromere.Asprophase

endsandmetaphasebegins,thecondensedchromosomesbecomeassociatedwiththe

spindle.Eventuallythechromosomesbecomearrangedinaplane(calledthemetaphaseplate)ata

rightangletothespindlefibers.Next,duringanaphase,thetwosisterchromatidsofeachchromosome

split,andonefromeachpairisdrawntowardeachpoleofthecell.Duringtelophasenuclearenvelopes

begintoformaroundeachsetofchromosomes,anddivisionofthecytoplasmtakesplace.

生物學家將有絲分裂劃分為4個階段。分裂前期，高度濃縮的兩個染色單體通過著絲粒連接在

一起。在分裂前期后期和分裂中期前期，濃縮的染色體與紡錘體相連，最后以正確的角度排列

在赤道板上。在分裂后期，兩個姊妹單體分離，分別拽向細胞兩極。在分裂末期，在每套染色

體周圍形成核膜，細胞質發(fā)生分裂。

Asmitosisproceeds,thespindlemicrotubulesplayacrucialroleinensuringthatbothpairedand

separatedchromatidsmoveintherightdirectionsatthepropertimes.Eachhalfofthespindleforms

asmicrotubulesextendfromeachpoleofadividingcelltotheregionofthemetaphaseplate.During

prophase,othermicrotubules,thecentromericfibers,extendoutwardfromthespindlepolesto

structuresonthechromosomescalledkinetochores.Duringanaphasethefibersbegintoshorten,and

thechromatidsbegintomoveapart.

在有絲分裂過程中，是紡錘體微管確保了染色單體在適當時間以正確方向進行分離。紡錘體微

管由兩極向赤道板延伸。在分裂前期，其它微管，著絲粒纖維延伸到染色體的動粒。在分裂后

期，纖維開始變短，染色單體分離。

Thespindleformsdifferentlyinplantandanimalcells.Inanimalsitisassociatedwithcentriole,while

inplantandfungalcellsspindleformationisassociatedwithreionscalledmicrotubuleorganizing

centers.

植物和動物細胞形成的紡錘體不同。動物細胞與中心粒相連，而在植物和真菌細胞中，紡錘體

與微管組織中心的離子相連。

Cytokinesis:PartitioningtheCytoplasm

胞質分裂：細胞質分離

Thedivisionofthecellcytoplasmattheendofmitosisiscalledcytokinesis.Inanimalcellsittakesplace

asaringofactinfilamentscontractsaroundthecellequator,pinchingthecellintwo.Inplantcells,

whichareboundedbyacellwall,cytokinesisinvolvesthebuildingofanewcellplateacrossthedividing

cellatitsequator.Cellwallmaterialisthendepositedintheregionofthecellplate.

在動物細胞中，環(huán)形肌動蛋白絲延赤道板收縮而使細胞一分為二。在植物細胞中，在赤道板形

成新的細胞板。

Meiosis:TheBasisofSexualReproduction

Meiosisisaspecialformofcelldivisionthattakesplaceinthereproductiveorgansthatproducesex

cells.Likemitosis,ittakesplaceafterDNAreplicationhasoccurredandinvolvestwosequentialnuclear

divisions(meiosisIandmeiosisII).Thesedivisionsresultinfourdaughtercells,eachwithhalfthe

numberofchromosomesoftheparentcell.Thephenomenonofcrossingoverduringmeiosisresults

inexchangesofgeneticinformationbetweenchromosomes.Hence,thehomologouschromosomes

distributedtodifferentprogenycellsarenotidentical.

減數(shù)分裂是性細胞分裂的特殊形式。如有絲分裂，它也是發(fā)生在DNA復制后并有連續(xù)的兩個核

分裂。產(chǎn)生4個子細胞，分別含有親本一半的染色體數(shù)。

Asinmitosistwochromatidsexistforeachchromosomeatthebeginningofprophase1.Duringthis

phasethehomologouschromosomesundergosynapsis,orpairing,whichisbroughtaboutbyabridging

structureofproteinsandRNAcalledthesynaptonemalcomplex.Thehomologouspairsstaytogether

whentheyalignonthemetaphaseplate.Unliketheanaphaseofmitosis,however,duringanaphaseI

thetwochromatidsofeachchromosomestayjoinedatthecentromereandmovetogethertooneof

thetwopolesofthecell.Itisthiseventthatresultsinthehalvingofthechromosomenumberinthe

fourdaughtercellsthatresultfrommeiosis.

正如在有絲分裂中一樣，兩個同源染色單體通過蛋白質和RNA橋配對形成聯(lián)會復合體。與有絲

分裂不同的是，每組染色體的兩個染色單體連接在著絲點上并一起移向細胞兩極的一級。由此

而導致4個子細胞染色體數(shù)減半。

DuringtelophaseInuclearenvelopesenclosethechromosomesinnuclei,andinmostspecies

cytokinesis(thefirstnucleardivision)follows.ThesecondnucleardivisionbeginswithmetaphaseII,

inwhichthechromosomesineachdaughtercellagainalignonametaphaseplate.Thecentromeres

finallydivide,andeachsisterchromatidmovestooneofthepolesofthespindle.Thenextphaseis

telophase,followedagainbycytokinesis.Theresultoftheentireprocessisfourhaploidcellsinwhich

parentalchromosomesarerandomlydistributed.

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(chǎn)生4個單倍體，父母染色體隨機分配。

AsexualVersusSexualReproduction

Mitosisandmeiosis,respectively,makesimplecelldivisionandsexualreproductionpossible.Each

meansofpassingonhereditaryinformationhasadvantages.Inasexualreproductiontheparent

organismgivesrisetooffspringthataregeneticclonesoftheparent.Theadvantagesofthistypeof

reproductionarethatitpreservestheparent'ssuccessfulgeneticcomplement,requireslittleorno

specializationofreproductiveorgans,andismorerapidthansexualreproduction.Amajor

disadvantageoftheasexualmodeisthatasinglecatastrophiceventordiseasemaydestroyanentire

populationofgeneticallyidenticalorganisms.Aprimebenefitofsexualreproductionisthatitprovides

geneticvariabilityandareadymechanismfortheeliminationofdeleteriousmutations.Italsoallows

"new"geneformstoariseandspreadthroughpopulations.

有絲分裂和成數(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(chǎn)生新的基因并在種群中蔓延。

第四課

FoundationsofGenetics

EarlyTheoriesofinheritanee

EarlyideasofinheritanceincludedHippocrates'theoryofpangenesisandAugust

Weismandsgermplasmtheory.Basedonexperimentswithmice,Weismannproposedthat

hereditaryinformationingametestransmittedtraitstoprogeny.Bothoftheseearlyviews

incorporatedtheblendingtheory:theyheldthatheritabletraitsofthetwoparentsblend,so

thatthedistinctcharacteristicsofeacharelostinoffspring.

遺傳學的早期理論包括泛生說和種質理論?；谛∈髮嶒灒S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。

GregorMendelandtheBirthofGenetics

GregorMendel,anAugustinianmonkinthemonasteryatBrunn,Austria,isknownasthe"father

ofgenetics."Havingbeenexposedtotheoriesoftheparticulatenatureofmatterwhilea

universitystudentandhavingabackgroundinmathematics,Mendelcarriedoutaseriesof

carefullyplannedexperimentsthatdemonstratedtheparticulatenatureofheredity.His

revolutionaryideaswereneitherunderstoodnoraccepteduntilmanyyearsafterMendeldied.

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。

Mendel'sClassicExperiments

Mendelstudiedgeneticsthroughplant-breedingexperimentswiththegardenpea,aplant

speciesthatisself-fertilizingandbreedstrue(eachoffspringisidenticaltotheparentinthe

traitofinterest).Totesttheblendingtheory,hefocusedhisresearchonsevendistinct

characters.Eachofthesecharacters,suchasseedcolorandplantheight,presentonlytwo,

clear-cutpossibilities.Healsorecordedthetypeandnumberofallprogenyproducedfrom

eachpairofparentpeaplants,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(chǎn)生的每一個子代類型和數(shù)量，在雜交產(chǎn)生子2代。

Foreachofthecharactershestudied,Mendelfoundthatonetraitwasdominantwhiletheother

wasrecessive.lnthesecondfilial(F2)generation,theratioofdominanttorecessivewas3:1.Mendel

deducedthatthisresultwaspossibleonlyifeachindividualpossessesonlytwohereditaryunits,

onefromeachparent.TheunitsMendelhypothesizedaretodayknownasalleles,alternativeforms

ofgenes.Genesarethebasicunitsofheredity.Anorganismthatinheritsidenticalallelesforatrait

fromeachparentissaidtobehomozygousforthattrait;ifdifferentallelesforatraitareinherited,

theorganismisheterozygousforthattrait.Whenanorganismisheterozygousforatrait,the

resultingphenotypeforthattraitexpressesonlythedominantallele.Thus,theorganism'

sphenotype—itsphysicalappearanceandproperties-differsfromitsgenotype,whichmayinclude

bothadominantandarecessiveallele.Apictorialrepresentationofallpossiblecombinationsof

ageneticcrossisknownasaPunnettsquare.

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'sfirst

law:thelawofsegregation.Thislawstatesthatforagiventraitanorganisminheritsoneallele

fromeachparent.Togethertheseallelesformtheallelepair.Whengametesareformedduring

meiosis,t