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1、可锐教育官网 http:/2018 年可锐考研第一轮复习之英语阅读（一）Until about five years ago, the very idea that peptide hormonesmight be made anywhere in the brain besides the hypothalamus was astounding.Peptide hormones, scientists thought, were made by endocrine glands and thehypothalamus was thought to be the brains only end
2、ocrinegland. What is more, because peptide hormones cannot cross the blood-brainbarrier, researchers believed that they never got to any part of the brainother than the hypothalamus, where they were simply produced and then releasedinto the bloodstream. But these beliefs about peptide hormones were
3、questioned aslaboratory after laboratory found that antiserums to peptide hormones, wheninjected into the brain, bind in places other than the hypothalamus, indicatingthat either the hormones or substances that cross-react with the antiserums arepresent. The immunological method of detecting peptide
4、 hormones by means ofantiserums, however, is imprecise. Cross-reactions are possible and this methodcannot determine whether the substances detected by the antiserums really arethe hormones, or merely close relatives. Furthermore, this method cannot beused to determine the location in the body where
5、 the detected substances areactually produced. New techniques of molecular biology, however, provide a way toanswer these questions. It is possible to make specific complementary DNAs that canserve as molecular probes seek out the messenger RNAs of thepeptide hormones. If brain cells are making the
6、hormones, the cells will containthese mRNAs. If the products the brain cells make resemble the hormones butare not identical to them, then the c DNAs should still bindto these mRNAs, but should not bind as tightly as they would to m RNAs for thetrue hormones. The cells containing these mRNAs can the
7、n beisolated and their mRNAs decoded to determine just what their protein products are and howclosely the products resemble the true peptide hormones. The molecular approach to detecting peptide hormones using cDNAprobes should also be much faster than the immunological method because it cantake yea
8、rs of tedious purifications to isolate peptide hormones and thendevelop antiserums to them. Roberts, expressing the sentiment of manyresearchers, states: “I was trained as an endocrinologist. But it became clear to me thatthe field of endocrinology needed molecular biology input. The process ofgrind
9、ing out protein purifications is just too slow.” If, as the initial tests with cDNA probes suggest, peptide hormonesreally are made in brain in areas other than the hypothalamus, a theory must bedeveloped that explains their function in the brain. Some have suggested thatthe hormones are all growth
10、regulators, but Rosens work on rat brainsindicates that this cannot be true. A number of other researchers propose thatthey might be used for intercellular communication in the brain. 可锐教育官网 http:/1.Which of the following titles best summarizes the text? A Is Molecular Biology the Key to Understandi
11、ng Intercellular Communicationin the Brain? B Molecular Biology: Can Researchers Exploit Its Techniques to SynthesizePeptide Hormones? C The Advantages and Disadvantages of the Immunological Approach to DetectingPeptide Hormones. D Peptide Hormones: How Scientists Are Attempting to Solve Problems of
12、 TheirDetection and to Understand Their Function? 2.The text suggests that a substance detected in the brain by use of antiserumsto peptide hormones may A have been stored in the brain for a long period of time. B play no role in the functioning of the brain. C have been produced in some part of the
13、 body other than the brain. D have escaped detection by molecular methods. 3.According to the text, confirmation of the belief that peptide hormones arecreated in the brain in areas other than the hypothalamus would forcescientists to A reject the theory that peptide hormones are made by endocrine g
14、lands. B revise their beliefs about the ability of antiserums to detect peptidehormones. C invent techniques that would allow them to locate accurately brain cellsthat produce peptide hormones. D develop a theory that account for the role played by peptide hormones inthe brain. 4.Which of the follow
15、ing is mentioned in the text as a drawback of theimmunological method of detecting peptide hormones? A It cannot be used to detect the presence of growth regulators in the brain. B It cannot distinguish between the peptide hormones and substances that arevery similar to them. C It uses antiserums that are unable to cross the blood-brain barrier. D It involves a purification process that requires extensive training inendocrinology. 5.The idea that the field of endocrinology can gain from developments inmolecular biology is regarded by Roberts with A incredulity. B derision. C indifference
