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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,
5 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
10 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
15 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
20 (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.
(187 words)
11. Which of the following titles best summarizes the
passage?
(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) Peptide Hormones: How Scientists Are
Attempting to Solve Problems of Their
Detection
(E) Peptide Hormones: The Role Played by
Messenger RNA‘s in Their Detection
12. 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
13. Which of the following is mentioned in the passage
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 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.
(E) It involves injecting foreign substances directly
into the bloodstream. |
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发表于 2011-11-4 08:08:45
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