GRE Reading Comprehension
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Source: CHP
Until about five years ago, the very idea that peptide hormones might be made anywhere in the brain besides the hypothalamus was astounding. But 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. The 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 used to determine the location 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 DNA's (cDNA‘s) that can serve as molecular probes to seek out the messenger RNA's (mRNA‘s) of the peptide hormones. The brain cells containing these mRNA's can then be isolated and their mRNA's decoded to determine just what their protein products are and how closely the products resemble the true peptide hormones.
The passage suggests that a substance detected in the brain by use of antiserums 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
- E play an important role in the functioning of the hypothalamus