生物学导论 第1集 文本下.docx
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生物学导论 第1集 文本下.docx
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生物学导论第1集文本下
麻省理工大学
生物学导论
第1集下
文本
AndpeoplecomeuptomeafterwardseachsemestereachyearandsayProfessorWeinberg,whydon’tyoutalksimple,whydon’tyoutalkthewayweheardthingsinhighschool?
AndpleaseunderstandthatifIusebigwordssometimes.
It’stobroadenyourvocabularysoyoucanlearnbigwords.Oneofthethingsyoushouldbeable,oneofthebigtakehomelessonsofthiscourseshouldbethatyourvocabularyisexpanded.NotjustyourscientificvocabularybutyourgeneralworkingEnglishvocabulary.Perhapsthebiggestgoalofthiscourse,bytheway,isnotthatyoulearnthenamesofalltheorganellesandcellsbutthatyoulearnhowtothinkinascientificandrationalway.Notjustbecauseofthiscoursebutthatthiscoursehelpsyoutodoso.
Andassuch,wedon’tplacethatmuchemphasisonmemorizationbuttobeabletothinklogicallyaboutscientificproblems.Herewecanbegintoseethemetaphytaandherearetheprotozoadifferentwordsforallofthese.Andhereweseeourownphylum,thechordates.And,again,keepinmindthatthislinerightdownhereisabout550to600millionyearsago,justtogiveyouatimescaleforwhat’sbeengoingon,onthisplanet.
Onepointwe’llreturntorepeatedlythroughoutthesemesteristhatalllifeformsonthisplanetarerelatedtooneanother.It’snotasiflifewasinvertedmultipletimesonthisplanetandthattherearemultipleindependentinventionstotheextent,thatlifearosemorethanonceonthisplanet,anditmayhave.Theotheralternativeorcompetinglifeformswereseenwipedoutbyourancestors,oursingle-cellular3billionyearsago.And,therefore,everythingthatexiststodayonthisplanetrepresentsthedescendentsofthatsuccessfulgroupofcellsthatexistedaverylongtimeago.
Herewehaveallthisfamilytreeofthedifferentmetazoanformsthathavebeencreatedbythefloridhandofevolution.Andwe’renotgoingtostudythosephylogeniessimplybecausewewanttounderstandprinciplesthatexplainallofthem.Notjusthowthisorthatparticularorganismisabletodigestitsfoodorisabletoreproduce.Here’sanotherthingwe’renotgoingtotalkabout.We’renotgoingtotalkaboutcomplicatedlifeforms.We’renotgoingtotalkverymuch,infacthardlyatallaboutecology.Thisisjustonesuchthing,thewaythataparasiteisableto,atapewormisabletoinfectpeople.Thisis,again,I’mshowingyouthisnottosaythiswhatwe’regoingtotalkabout,we’renotgoingtotalkaboutthat.
There’sawealthofdetailthat’sknownaboutthewaylifeexistsinthebiospherethatwe’resimplygoingtoturnourbacksonbyfocusingonsomebasicprinciples.We’realsonotgoingtotalkaboutanatomy.Hereinquickorderaresomeoftheanatomies.Youmayhavelearnedaboutinhighschool,andI’mgivingthemtoyoueachwithathree-secondminute,athree-secondshowingtosaywe’renotgoingtodoallthis.Andratherjusttoreinforceourfocus,we’regoingtolimitourselvestoaveryfinitepartofthebiosphere.Andhereisonewayofdepictingthebiosphere.It’sobviouslyanarbitrarywayofdoingsobutit’squiteillustrative.Herewestartfrommolecules.And,infact,wewilloccasionallygodowntosubmolecularatoms.Andhere’sthenextdimensionofcomplexity,organelles.
Thatisthesespecializedlittleorganswithincells.We’regoingtofocusoncells.Andwhenwestartgettingtotissues,we’regoingtostartnottalkingsomuchaboutthem.Andwe’renotgoingtotalkaboutorganismsandorgansorentireorganismsorhighercomplexecologicalcommunities.Andthereasonwe’redoingthatisthatfor40yearsinthisdepartment,andincreasingintherestoftheworldthereistheacceptanceofthenotionthatifweunderstandwhatgoesondownhereinthesefirstthreestepswecanunderstandalmosteverythingelseinprinciple.Ofcourse,inpracticewemaynotbeabletoapplythoseprinciplestohowanorganismworksortohowthehumanbrainworksyet.Maybeweneverwill.But,ingeneral,ifonebeginstounderstandtheseprinciplesdownhere,onecanunderstandmuchabouthoworganismicembryologicdevelopoccurs,onecanunderstandalotaboutawholevarietyofdiseaseprocesses,onecanunderstandhowoneinheritsdiseasesusceptibilities,andonecanunderstandwhymanyorganismslookthewaytheydo,i.e.theprocessofdevelopmentalbiology.Andso,keepinmindthatifyoucametohearaboutallofthesethingswe’regoingtoletyoudown.That’snotwhatthisisgoingtobeabout.Thisalsodictatesthedimensionsoftheuniversethatwe’regoingtotalkaboutbecausewe’regoingtolimitourselvestothevery,verysmallandnottothemicroscopic.Onsomeoccasionswe’lllimitourselvestoitemsthataresosmallyoucannotseetheminthelightmicroscope.Onotheroccasionswemaywidenourgazetolookatthingsthatareaslargeasamillimeter,butbasicallywe’restayingvery,verysmall.Again,becauseweview,correctlyornot,thefactthatthebigprocessescanbeunderstoodbydelvingintothemoleculardetailsofwhathappensinvisiblyandcannotbeseebymostwaysofvisualizingthings,includingthelightandofteneventheelectronmicroscope.Keepinmindthat50yearsagowedidn’tknowanyofthis,forallpracticalpurposes,orverylittleofthis.Andkeepinmindthatwe’resoclosetothisrevolutionthatwedon’treallyunderstanditsramifications.Iimagineitwillbeanother50yearsbeforewereallybegintoappreciatethefallout.Thelong-termconsequencesofthisrevolutioninbiologywhichbegin51yearsago.Andsoyou’repartofthatandyou’regoingtoexperienceitmuchmorethanmygenerationdid.AndindeedoneofthereasonswhyMITdecidedabout10to12yearsagothateveryMITundergraduateneededtohaveatleaseonesemesterofbiologyisthatbiology,inthesamewayasphysicsandchemistryandmath,hasbecomeanintegralpartofeveryeducatedperson’sknowledgebaseintermsoftheirabilitytodealwiththeworldinarationalway.Intermsofpublicpolicy,intermsofallkindsofethicalissues,theyneedtounderstandwhat’sreallygoingon.Manyoftheissuesthatonetalksabouttodayaboutbioethicsarearticulatedbypeoplewhohaven’tthevaguestideaaboutwhatwe’retalkingaboutthissemester.Youwillknowmuchmorethantheywill,andhopefullysometimedowntheroad,whenyoubecomemoreandmoreinfluentialvoicesinsociety,you’llbeabletocontributewhatyouunderstandhere,whatyoulearnedheretothatdiscussion.Rightnowmuchofbioethicaldiscussionisfueledbypeoplewhohaven’tthevaguestideawhataribosomeormitochondrionorevenageneisandthereforeisoftenadiscussionofmutuallysharedignorancewhichyoucandiffusebylearningsomebasics,bylearningsomeoftheessentials.Hereisthecomplexityofthecellwe’regoingtofocusonlargelythissemester,whichistosaytheeukaryoticratherthantheprokaryoticcell.Andthisisjusttogiveyouafeelingfortheoveralldimensionsofthecellandrefertomanyofthelandmarksthatwillrepeatedlybebroughtupduringthecourseofthissemester.Hereisthenucleus.ThetermkarioncomesfromtheGreekmeaningaseedorakernel.Andthenucleusiswhatgivestheeukaryoticcellitsname.Withinthenucleus,althoughnotshowhere,arethechromosomeswhichcarryDNA.Youmayhavelearnedthatalongtimeago.Outsideofthenucleusidthisentirevastarrayoforganellesthatgoesfromthenuclearmembrane,andI’mpointtoitrighthere,allthewayouttotheoutsideofthecell.Theoutsidelimitingmembrane.Theoutermembraneofthecelliscalledtheplasmamembrane.Andbetweenthenucleusandtheplasmamembranethereisanenormousamountofbiologicalandbiochemicalactivitytakingplace.Hereare,forexample,themitochondria.Andthemitochondria,asonehasleaned,arethesourcesofenergyproductioninthecell.And,therefore,we’lltouchonthemverybriefly.Thisisanartist’sconceptionofwhatamitochondrionlookslike.Almostalwaysartists’conceptionsofthesethingshaveonlyvagueresemblancetothereality.But,inanycase,youcanbegintogetafeelingforwhatonethinksabouttheirappearance.Herearemitochondriaslicedopenbythehandoftheartist.And,interestingly,mitochondriahavetheirownDNAinthem.Onenowacceptsthefactthatmitochondriaarethedescendentsofbacteriawhichinsinuatedthemselvesintothecytoplasmsoflargecells.Roughly1.5billionyearsagoandbegantodoaspecializedjobwhichincreasinglybecamethejobofenergyproductionwithincells.Tothisday,mitochondriaretainsomevestigialattributesofthebacterialancestorswhichinitiallycolonizedorparasitizedthecytoplasmofthecell.WhenIsayparasitized,youmightimaginethatthemitochondriaaretakingadvantageofthecell.But,infact,themitochondriarepresenttheessentialsourcesofenergyproductioninthecell.Withoutourmitochondria,asyoumightlearnbytakingcyanide,forexample,youdon’tliveforverymanyminutes.AndthevestigesofbacterialoriginsofmitochondriastillhavetheirownDNAmolecule,theirownchromosome.Theystillhavetheirownribosomesandproteinsyntheticapparatus,eventhoughthevastmajorityoftheproteinsinsidemitochondriaareimportedfromthecytoplasm,i.e.,thesevestigialbacterianowrelyonproteinscominginmadebythecellatlargethatareimportedintothemitochondriontosupplementthesmallnumberofvestigialbacterialproteinswhicharestillmadehereinsidethemitochondrionandusedforessentialfunctioninenergyproduction.HereistheGolgiapparatus.AndtheGolgiapparatusuphereisusedfortheproductionofmembranes.Asonewilllearnthroughoutthesemester,themembra
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