No.8 -1 section 6 长阅读
关于peptide hormones 的那个。
23、Accordingto the passage, confirmation of the belief that peptide hormones are made inthe brain in areas other than the hypothalamus would force scientists to
(A) （1）reject the theory that peptide hormones are madeby endocrine glands (B) （2）revise their beliefs about the ability ofantiserums to detect peptide hormones (C) （3）invent techniques that would allow them to locateaccurately brain cells that produce peptide hormones (D) （4）search for techniques that would enable them todistinguish peptide hormones from their close relatives（E） (E) （5）develop a theory that explains the role played bypeptide hormones in the brain 答案我觉得应该是A啊。定位红色处不是正好么？为什么是E？？？
答
Until about fiveyears ago, the very idea that peptide (peptide: n.缩氨酸) hormones might bemade anywhere in the brain besides the hypothalamus was astounding. Peptidehormones, scientists thought, were made by endocrine glands and thehypothalamus was thought to be the brains’ only endocrine gland. What is more,because peptide hormones cannot cross the blood-brain barrier, researchers believedthat they never got to any part of the brain other than the hypothalamus, wherethey were simply produced and then released into the bloodstream. But these beliefsabout peptide hormones were questioned as laboratory after laboratory foundthat antiserums to peptide hormones, when injected into the brain, bind inplaces other than the hypothalamus, indicating that either the hormones orsubstances that cross-react with the antiserums are present. The immunologicalmethod of detecting peptide hormones by means of antiserums, however, isimprecise. Cross-reactions are possible and this method cannot determinewhether the substances detected by the antiserums really are the hormones, ormerely close relatives. Furthermore, this method cannot be used to determinethe location in the body where the detected substances are actually produced. New techniques ofmolecular biology, however, provide a way to answer these questions. It ispossible to make specific complementary DNA’s (cDNA’s) that can serve asmolecular probes to seek out the messenger RNA’s (mRNA’s) of the peptidehormones. If brain cells are making the hormones, the cells will contain these mRNA’s.If the products the brain cells make resemble the hormones but are notidentical to them, then the cDNA’s should still bind to these mRNA’s, butshould not bind as tightly as they would to mRNA’s for the true hormones. Thecells containing these mRNA’s can then be isolated and their mRNA’s decoded todetermine just what their protein products are and how closely the productsresemble the true peptide hormones. The molecularapproach to detecting peptide hormones using cDNA probes should also be muchfaster than the immunological method because it can take years of tediouspurifications to isolate peptide hormones and then develop antiserums to them.Roberts, expressing the sentiment of many researchers, states: “I was trainedas an endocrinologist. But it became clear to me that the field ofendocrinology needed molecular biology input. The process of grinding outprotein purifications is just too slow.” If, as the initialtests with cDNA probes suggest, peptide hormones really are made in the brainin areas other than the hypothalamus, a theory must be developed that explainstheir function in the brain. Some have suggested that the hormones are allgrowth regulators, but Rosen’s work on rat brains indicates that this cannot betrue. A number of other researchers propose that they might be used forintercellular communication in the brain. | 
发表于 2012-4-21 19:25:31
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