08新版gmat閱讀-講義

1、新東方在線[]網(wǎng)絡(luò)課堂電子教材系列GMAT閱讀講義1GMAT閱讀講義閱讀講義主講：王鵬主講：王鵬歡迎使用新東方在線電子教材歡迎使用新東方在線電子教材GMAT核心閱讀核心閱讀Passage1Caffeinethestimulantincoffeehasbeencalled“themostwidelyusedpsychoactivesubstanceonEarth.”SynderDalyBrunshaverecentlyproposedth

2、atcaffeineaffectsbehavibycounteringtheactivityin(5)thehumanbrainofanaturallyoccurringchemicalcalledadenosine.Adenosinenmallydepressesneuronfiringinmanyareasofthebrain.Itapparentlydoesthisbyinhibitingthereleaseofneurotran

3、smitterschemicalsthatcarrynerveimpulsesfromoneneurontothenext.(10)Likemanyotheragentsthataffectneuronfiringadenosinemustfirstbindtospecificreceptsonneuronalmembranes.Thereareatleasttwoclassesofthesereceptswhichhavebeende

4、signatedA1A2.Snyderetalproposethatcaffeinewhichisstruc(15)turallysimilartoadenosineisabletobindtobothtypesofreceptswhichpreventsadenosinefromattachingthereallowstheneuronstofiremereadilythantheyotherwisewould.Fmanyyearsc

5、affeine’seffectshavebeenattri(20)butedtoitsinhibitionoftheproductionofphosphodiesteraseanenzymethatbreaksdownthechemicalcalledcyclicAMP.AnumberofneurotransmittersexerttheireffectsbyfirstincreasingcyclicAMPconcentrationsi

6、ntargetneurons.Therefeprolongedperiodsat(25)theelevatedconcentrationsasmightbebroughtaboutbyaphosphodiesteraseinhibitcouldleadtoagreater新東方在線[]網(wǎng)絡(luò)課堂電子教材系列GMAT閱讀講義3(C)increasescyclicAMPconcentrationsintargetneuronswhereasa

7、denosinedecreasessuchconcentrations(D)permitsreleaseofneurotransmitterswhenitisboundtoadenosinereceptswhereasadenosineinhibitssuchrelease(E)inhibitsbothneuronfiringtheproductionofphosphodiesterasewhenthereisasufficientco

8、ncentrationinthebrainwhereasadenosineinhibitsonlyneuronfiring3.InresponsetoexperimentalresultsconcerningIBMXSnyderetalcontendedthatitisnotuncommonfpsychoactivedrugstohave(A)mixedeffectsinthebrain(B)inhibityeffectsonenzym

9、esinthebrain(C)closestructuralrelationshipswithcaffeine(D)depressiveeffectsonmouselocomotion(E)theabilitytodislodgecaffeinefromreceptsinthebrain4.AccdingtoSnyderetalallofthefollowingcompoundscanbindtospecificreceptsinthe

10、brainEXCEPT(A)IBMX(B)caffeine(C)adenosine(D)theophylline(E)phosphodiesterase5.Snyderetalsuggestthatcaffeine’sabilitytobindtoA1A2receptscanbeatleastpartiallyattributedtowhichofthefollowing(A)Thechemicalrelationshipbetween

11、caffeinephosphodiesterase(B)Thestructuralrelationshipbetweencaffeineadenosine(C)Thestructuralsimilaritybetweencaffeineneurotransmitters(D)Theabilityofcaffeinetostimulatebehavi(E)Thenaturaloccurrenceofcaffeineadenosineint

12、hebrain6.TheauthquotesSnyderetalinlines3843mostprobablyinderto(A)revealsomeoftheassumptionsunderlyingtheirthey(B)summarizeamajfindingoftheirexperiments(C)pointoutthattheirexperimentswerelimitedtothemouse(D)indicatethatth