2017英语专八阅读100篇高级篇附答案解析（77）

2017英语专八阅读100篇高级篇附答案解析（77）

　　Until about five years ago, the very idea that peptide 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 ismore, because peptide hormones cannot cross the blood-brain barrier,researchers believed that they never got to any part of the brain other thanthe hypothalamus, where they were simply produced and then released into thebloodstream.

　　But these beliefs about peptide hormones were questioned as laboratoryafter laboratory found that antiserums to peptide hormones, when injected intothe brain, bind in places other than the hypothalamus, indicating that eitherthe hormones or substances that cross-react with the antiserums are present.The immunological method of detecting peptide hormones by means of antiserums,however, is imprecise. Cross-reactions are possible and this method cannotdetermine whether the substances detected by the antiserums really are thehormones, or merely close relatives. Furthermore, this method cannot be used todetermine the location in the body where the detected substances are actuallyproduced.

　　New techniques of molecular biology, however, provide a way to answerthese questions. It is possible to make specific complementary DNA’s that can serve as molecularprobes seek out the messenger RNA’s of the peptide hormones. If brain cells are making the hormones, thecells will contain these mRNA’s. If the products the brain cells make resemble the hormones but are notidentical to them, then the c DNA’s should still bind to these mRNA’s, but should not bind as tightlyas they would to m RNA’s for the true hormones. The cells containing these mRNA’s can then be isolated and theirmRNA’s 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 cDNA probes shouldalso be much faster than the immunological method because it can take years oftedious purifications to isolate peptide hormones and then develop antiserumsto them. Roberts, expressing the sentiment of many researchers, states: “I was trained as an endocrinologist.But it became clear to me that the field of endocrinology needed molecularbiology input. The process of grinding out protein purifications is just tooslow.”

　　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 regulators, but Rosen’s work on rat brains indicatesthat this cannot be true. A number of other researchers propose that they mightbe used for intercellular communication in the brain.

　　1. Which of the following titles best summarizes the text?

　　[A] Is Molecular Biology the Key to Understanding IntercellularCommunication in the Brain?

　　[B] Molecular Biology: Can Researchers Exploit Its Techniques toSynthesize Peptide Hormones?

　　[C] The Advantages and Disadvantages of the Immunological Approach toDetecting Peptide Hormones.

　　[D] Peptide Hormones: How Scientists Are Attempting to Solve Problems ofTheir Detection and to Understand Their Function?

　　2. The text suggests that a substance detected in the brain by use ofantiserums to 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 body other than the brain.

　　[D] have escaped detection by molecular methods.

　　3. According to the text, confirmation of the belief that peptidehormones are created in the brain in areas other than the hypothalamus wouldforce scientists to

　　[A] reject the theory that peptide hormones are made by endocrine glands.

　　[B] revise their beliefs about the ability of antiserums to detectpeptide hormones.

　　[C] invent techniques that would allow them to locate accurately braincells that produce peptide hormones.

　　[D] develop a theory that account for the role played by peptide hormonesin the brain.

　　4. Which of the following 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 thebrain.

　　[B] It cannot distinguish between the peptide hormones and substancesthat are very 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 trainingin endocrinology.

　　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.

　　[D] enthusiasm.

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