Untilaboutfiveyearsago,theveryideathatpeptidehormonesmightbemadeanywhereinthebrainbesidesthehypothalamuswasastounding.Peptidehormones,scientiststhought,weremadebyendocrineglandsandthehypothalamuswasthoughttobethebrains’onlyendocrinegland.Whatismore,becausepeptidehormonescannotcrosstheblood-brainbarrier,researchersbelievedthattheynevergottoanypartofthebrainotherthanthehypothalamus,wheretheyweresimplyproducedandthenreleasedintothebloodstream.Butthesebeliefsaboutpeptidehormoneswerequestionedaslaboratoryafterlaboratoryfoundthatantiserumstopeptidehormones,wheninjectedintothebrain,bindinplacesotherthanthehypothalamus,indicatingthateitherthehormonesorsubstancesthatcross-reactwiththeantiserumsarepresent.Theimmunologicalmethodofdetectingpeptidehormonesbymeansofantiserums,however,isimprecise.Cross-reactionsarepossibleandthismethodcannotdeterminewhetherthesubstancesdetectedbytheantiserumsreallyarethehormones,ormerelycloserelatives.Furthermore,thismethodcannotbeusedtodeterminethelocationinthebodywherethedetectedsubstancesareactuallyproduced.Newtechniquesofmolecularbiology,however,provideawaytoanswerthesequestions.ItispossibletomakespecificcomplementaryDNA’s(cDNA’s)thatcanserveasmolecularprobesseekoutthemessengerRNA’s(mRNA’s)ofthepeptidehormones.Ifbraincellsaremakingthehormones,thecellswillcontainthesemRNA’s.Iftheproductsthebraincellsmakeresemblethehormonesbutarenotidenticaltothem,thenthecDNA’sshouldstillbindtothesemRNA’s,butshouldnotbindastightlyastheywouldtomRNA’sforthetruehormones.ThecellscontainingthesemRNA’scanthenbeisolatedandtheirmRNA’sdecodedtodeterminejustwhattheirproteinproductsareandhowcloselytheproductsresemblethetruepeptidehormones.ThemolecularapproachtodetectingpeptidehormonesusingcDNAprobesshouldalsobemuchfasterthantheimmunologicalmethodbecauseitcantakeyearsoftediouspurificationstoisolatepeptidehormonesandthendevelopantiserumstothem.Roberts,expressingthesentimentofmanyresearchers,states:“Iwastrainedasanendocrinologist.Butitbecamecleartomethatthefieldofendocrinologyneededmolecularbiologyinput.Theprocessofgrindingoutproteinpurificationsisjusttooslow.”If,astheinitialtestswithcDNAprobessuggest,peptidehormonesreallyaremadeinbraininareasotherthanthehypothalamus,atheorymustbedevelopedthatexplainstheirfunctioninthebrain.Somehavesuggestedthatthehormonesareallgrowthregulators,butRosen’sworkonratbrainsindicatesthatthiscannotbetrue.Anumberofotherresearchersproposethattheymightbeusedforintercellularcommunicationinthebrain.(483)1.Whichofthefollowingtitlesbestsummarizesthetext?[A]IsMolecularBiologytheKeytoUnderstandingIntercellularCommunicationintheBrain?[B]MolecularBiology:CanResearchersExploitItsTechniquestoSynthesizePeptideHormones?[C]TheAdvantagesandDisadvantagesoftheImmunologicalApproachtoDetectingPeptideHormones.[D]PeptideHormones:HowScientistsAreAttemptingtoSolveProblemsofTheirDetectionandtoUnderstandTheirFunction?2.Thetextsuggeststhatasubstancedetectedinthebrainbyuseofantiserumstopeptidehormonesmay[A]havebeenstoredinthebrainforalongperiodoftime.[B]playnoroleinthefunctioningofthebrain.[C]havebeenproducedinsomepartofthebodyotherthanthebrain.[D]haveescapeddetectionbymolecularmethods.3.Accordingtothetext,confirmationofthebeliefthatpeptidehormonesarecreatedinthebraininareasotherthanthehypothalamuswouldforcescientiststo[A]rejectthetheorythatpeptidehormonesaremadebyen...
