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1、www.kaobo100.com中国考博辅导首选学校天津医科大学考博英语模拟真题及其解析Untilaboutfiveyearsago,theveryideathatpeptidehormonesmightbemadeanywhereinthebrainbesidesthehypothalamuswasastounding.Peptidehormones,scientiststhought,weremadebyendocrineglandsandthehypothalamuswasthoughttobethebrains’onlye
2、ndocrinegland.Whatismore,becausepeptidehormonescannotcrosstheblood-brainbarrier,researchersbelievedthattheynevergottoanypartofthebrainotherthanthehypothalamus,wheretheyweresimplyproducedandthenreleasedintothebloodstream.Butthesebeliefsaboutpeptidehormoneswerequestione
3、dasGengduoyuanxiaowanzhengkaoboyingyuzhentijiqijiexiqinglianxiquanguomianfeizixundianhua:silinglingliuliubaliujiuqiba,huojiazixunqq:qiqierliuqibawusanqilaboratoryafterlaboratoryfoundthatantiserumstopeptidehormones,wheninjectedintothebrain,bindinplacesotherthanthehypot
4、halamus,indicatingthateitherthehormonesorsubstancesthatcross-reactwiththeantiserumsarepresent.Theimmunologicalmethodofdetectingpeptidehormonesbymeansofantiserums,however,isimprecise.Cross-reactionsarepossibleandthismethodcannotdeterminewhetherthesubstancesdetectedbyth
5、eantiserumsreallyarethehormones,ormerelycloserelatives.Furthermore,thismethodcannotbeusedtodeterminethelocationinthebodywherethedetectedsubstancesareactuallyproduced.Newtechniquesofmolecularbiology,however,provideawaytoanswerthesequestions.Itispossibletomakespecificco
6、mplementarywww.kaobo100.com中国考博辅导首选学校DNA’s(cDNA’s)thatcanserveasmolecularprobesseekoutthemessengerRNA’s(mRNA’s)ofthepeptidehormones.Ifbraincellsaremakingthehormones,thecellswillcontainthesemRNA’s.Iftheproductsthebraincellsmakeresemblethehormonesbutarenotidenticaltothe
7、m,thenthecDNA’sshouldstillbindtothesemRNA’s,butshouldnotbindastightlyastheywouldtomRNA’sforthetruehormones.ThecellscontainingthesemRNA’scanthenbeisolatedandtheirmRNA’sdecodedtodeterminejustwhattheirproteinproductsareandhowcloselytheproductsresemblethetruepeptidehormon
8、es.ThemolecularapproachtodetectingpeptidehormonesusingcDNAprobesshouldalsobemuchfasterthantheimmunologicalmethodbecauseitcan
