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1、题目序号 题型归类第 1 题 中心主旨题型第 2 题 审题定位题型第 3 题 细节推导题型第 4 题 句间关系题型第 5 题 细节推导题型Until about five years ago, the very idea that peptide hormones might be made anywhere in the brain besides the hypothalamus was astounding. Peptide hormones, scientists thought, were made by endocrine glands and the hypothalamus w
2、as thought to be the brains only endocrine gland. What is more, because peptide hormones cannot cross the blood-brain barrier, researchers believed that they never got to any part of the brain other than the hypothalamus, where they were simply produced and then released into the bloodstream.But the
3、se beliefs about peptide hormones were questioned as laboratory after laboratory found that antiserums to peptide hormones, when injected into the brain, bind in places other than the hypothalamus, indicating that either the hormones or substances that cross-react with the antiserums are present. Th
4、e immunological method of detecting peptide hormones by means of antiserums, however, is imprecise. Cross-reactions are possible and this method cannot determine whether the substances detected by the antiserums really are the hormones, or merely close relatives. Furthermore, this method cannot be u
5、sed to determine the ocation in the body where the detected substances are actually produced.New techniques of molecular biology, however, provide a way to answer these questions. It is possible to make specific complementary DNAs (c DNAs) that can serve as molecular probes seek out the messenger RN
6、As (mRNAs) of the peptide hormones. If brain cells are making the hormones, the cells will contain these mRNAs. If the products the brain cells make resemble the hormones but are not identical to them, then the c DNAs should still bind to these mRNAs, but should not bind as tightly as they would to
7、m RNAs for the true hormones. The cells containing these mRNAs can then be isolated and their mRNAs decoded to determine just what their protein products are and how closely the products resemble the true peptide hormones.The molecular approach to detecting peptide hormones using cDNA probes should
8、also be much faster than the immunological method because it can take years of tedious purifications to isolate peptide hormones and then develop antiserums to them. Roberts, expressing the sentiment of many researchers, states: “I was trained as an endocrinologist. But it became clear to me that th
9、e field of endocrinology needed molecular biology input. The process of grinding out protein purifications is just too slow.”If, as the initial tests with cDNA probes suggest, peptide hormones really are made in brain in areas other than the hypothalamus, a theory must be developed that explains the
10、ir function in the brain. Some have suggested that the hormones are all growth regulators, but Rosens work on rat brains indicates that this cannot be true. A number of other researchers propose that they might be used for intercellular communication in the brain.1. Which of the following titles bes
11、t summarizes the text?A Is Molecular Biology the Key to Understanding Intercellular Communication in the Brain?B Molecular Biology: Can Researchers Exploit Its Techniques to Synthesize Peptide Hormones?C The Advantages and Disadvantages of the Immunological Approach to Detecting Peptide Hormones.D P
12、eptide Hormones: How Scientists Are Attempting to Solve Problems of Their Detection and to Understand Their Function?2. The text suggests that a substance detected in the brain by use of antiserums to peptide hormones mayA have been stored in the brain for a long period of time.B play no role in the
13、 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 peptide hormones are created in the brain in areas other than the hypothalamus would force scientists t
14、oA reject the theory that peptide hormones are made by endocrine glands.B revise their beliefs about the ability of antiserums to detect peptide hormones.C invent techniques that would allow them to locate accurately brain cells that produce peptide hormones.D develop a theory that account for the r
15、ole played by peptide hormones in the brain.4. Which of the following is mentioned in the text as a drawback of the immunological 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
16、 substances that 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 training in endocrinology.5. The idea that the field of endocrinology can gain from developments in molecular biology is regarded by Roberts withA incredulity.B derision.C indifference.D enthusiasm.答案与考点解析1. 【答案】D【考点解析】这是一道中心主旨题。全文从头至尾讨论的是“peptide hormones”在人体内产生的部位，所以有关全文
