搜索
可汗学院新SAT阅读真题下载到目前为止，新版SAT可汗学院官方不断放出更多真题，已经放出了68篇阅读，具体如下：Level222篇，Level321篇，Level417篇，8篇DiagnosticQuiz，共68篇阅读！想要下载可汗学院68篇阅读真题的同学，请移步：篇1PassageadaptedfromNikhilSwaminathan,Eat(Less)toLive(Longer),©2007byScientificAmerican.Scientistshaveknownformorethan70yearsthattheonesurefirewaytoextendthelivesofanimalswastocutcaloriesbyanaverageof30to40percent.Thequestionwas:Why?Nowanewstudybeginstounravelthemysteryandthemechanismbywhichreducingfoodintakeprotectscellsagainstagingandage-relateddiseases.ResearchersreportinthejournalCellthatthephenomenonislikelylinkedtotwoenzymes—SIRT3andSIRT4—inmitochondria(thecell'spowerhousethat,amongothertasks,convertsnutrientstoenergy).Theyfoundthatacascadeofreactionstriggeredbylowercaloricintakeraisesthelevelsoftheseenzymes,leadingtoanincreaseinthestrengthandefficiencyofthecellularbatteries.Byinvigoratingthemitochondria,SIRT3andSIRT4extendthelifeofcells,bypreventingflaggingmitochondriafromdevelopingtinyholes(orpores)intheirmembranesthatallowproteinsthattriggerapoptosis,orcelldeath,toseepoutintotherestofthecell.Wedidn'texpectthatthemostimportantpartofthispathwaywasinthemitochondria,saysDavidSinclair,anassistantprofessorofpathologyatHarvardMedicalSchoolandastudyco-author.Wethinkthatwe'vepossiblyfoundregulatorsofaging.In2003Sinclair'slabpublishedapaperinNaturethatdescribedthediscoveryofagenethatswitchedonintheyeastcellinresponsetocalorierestriction,whichSinclaircallsamasterregulatorinaging.Sincethen,histeamhasbeensearchingforananalogousgenethatplaysasimilarroleinthemammaliancell.TheresearchersdeterminedfromculturesofhumanembryonickidneycellsthatlowercaloricintakesendsasignalthatactivatesageneinsidecellsthatcodesfortheenzymeNAMPT(nicotinamidephosphoribosyltransferase).Thetwo-tofour-foldsurgeinNAMPTinturntriggerstheproductionofamoleculecalledNAD(nicotinamideadeninedinucleotide),whichplaysakeyroleincellularmetabolismandsignaling.TheuptickinNADlevelsactivatestheSIRT3andSIRT4genes,increasinglevelsoftheircorrespondingSIRT3andSIRT4enzymes,whichthenfloodtheinteriorofthemitochondria.Sinclairsayshe'snotsureexactlyhowSIRT3andSIRT4beefupthemitochondria'senergyoutput,butthateventsleadingtocelldeathareattheveryleastdelayedwhentherearevastquantitiesoftheenzymes.SIRT3andSIRT4arepartofafamilycalledsirtuins(SIRT1,whichhelpsextendcelllifebymodulatingthenumberofrepairproteinsfixingDNAdamagebothinsideandoutsidethecell'snucleus,isalsoamember).SIRTisshortforsir-2homologue—awell-studiedproteinthatisknowntoextendyeastcelllongevity.AccordingtoSinclair,allofthemammalianSIRTgenes(andtheirproteins)arepossibledrugtargetsfortherapiesaimedatextendinglife,aswellasstavingoffage-relatedillnesses,suchasAlzheimer'sdisease,cancersandmetabolicdisorders,likediabetes.IthinkSIRT3isthenextmostinterestingsirtuinfromadrugdevelopmentstandpoint,Sinclairsays.Itdoesprotectcells,butthere'sgrowingevidencethatitmaymediatethebenefitsofexerciseaswell.Sinclair'slabisnowworkingondevelopingwhathecallsapossiblesupermousewithelevatedlevelsofNAMPTtoseeifitliveslongerandismoredisease-resistantthannormalmice.MattKaeberlein,apathologistattheUniversityofWashingtoninSeattle,saysthatSinclair'steamhasaninterestinghypothesisconnectingthemitochondriatolongevity,butthatitneedstobemoredirectlytestedinthecontextofdietaryrestriction.IftheNAMPT-overexpressingmicearelong-livedanddiseaseresistant,thatwillprovidemoresupportforthisidea.LifespanofGroupsofMiceWithDifferentLevelsofCaloricReductionAdaptedfromWeindruchR,etal.(1986).TheRetardationofAginginMicebyDietaryRestriction:Longevity,Cancer,Immunity,andLifetimeEnergyIntake.JournalofNutrition,April,116(4),641-54.QUESTION1OF11Theauthorindicatesthatcaloricreductionextendsthelifeofamammaliancellby11TheauthorindicatesthatcaloricreductionextendsthelifeofamammaliancellbyA)turningoffthosegenesinvolvedinapoptosis,orcelldeath.B)forcingthemitochondriatoutilizedifferentenergysourcesforfuel.C)reducingtheproductionofNAD(nicotinamideadeninedinucleotide).D)initiatingaseriesofstepsthatresultsintheincreasedproductionofcertainenzymes.2Basedonthepassage,SIRT-3andSIRT-4indirectlyaffectcelllongevitybyA)strengtheningthemitochondrialmembrane.B)fixingdamagetothecell’sDNA.C)initiatingcelldeath.D)diminishingtheefficiencyofthecell’smitochondria.3Whichchoiceprovidesthebestevidencefortheanswertothepreviousquestion?A)lines7-9(“Researchers...mitochondria”)B)lines13-18(“By...cell.”)C)lines38-41(“The...mitochondria”)D)lines41-44(“Sinclair...enzymes”)94Theauthor’suseofthewords“powerhouse”and“batteries”inthesecondparagraphservesmainlytoA)emphasizethatmitochondriaarethemostimportantcomponentsofthecell.B)suggestthatmitochondriauseanelectricalgradienttoproduceenergyC)stressthatmitochondriaarethemainsourcesofenergyforthecell.D)implythatmitochondrianeedtoberechargedinordertofunctionefficiently5Asusedinline15(“flagging”),“flagging”mostnearlymeansA)breaking.B)shrinking.C)folding.D)weakening.6Themainpurposeofthefifthparagraph(lines30-37)istoA)suggestthatcaloricreductionhasadifferenteffectonyeastcellsthanmammal