2014年考研英语阅读的经典试题及答案(13)_大学英语阅读

2014年考研英语阅读的经典试题及答案(13)

　　New techniques of molecular biology, however, provide a way to answerthese questions. It is possible to make specific complementary DNAs that can serve as molecularprobes seek out the messenger RNAs of the peptide hormones. If brain cells are making the hormones, thecells will contain these mRNAs. If the products the brain cells make resemble the hormones but are notidentical to them, then the c DNAs should still bind to these mRNAs, but should not bind as tightlyas they would to m RNAs for the true hormones. The cells containing these mRNAs can then be isolated and theirmRNAs 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 Rosens 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.