2015年MBA阅读理解强化练习题13
Until about five years ago, the very idea that peptide hormones might bemade anywhere in the brain besides the hypothalamus was astounding. Peptide
hormones, scientists thought, were made by endocrine glands and the hypothalamus
was 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 these 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. 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 (c DNA’s) that
can serve as molecular probes seek out the messenger RNA’s (mRNA’s) of the
peptide hormones. If brain cells are making the hormones, the cells will contain
these mRNA’s. If the products the brain cells make resemble the hormones but are
not identical to them, then the c DNA’s should still bind to these mRNA’s, but
should not bind as tightly as they would to m RNA’s for the true hormones. The
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 molecular approach to detecting peptide hormones using cDNA probes
should 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 the
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 their function in the brain. Some have suggested that
the hormones are all growth regulators, but Rosen’s 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 best summarizes the text?
Is Molecular Biology the Key to Understanding Intercellular
Communication in the Brain?
Molecular Biology: Can Researchers Exploit Its Techniques to Synthesize
Peptide Hormones?
The Advantages and Disadvantages of the Immunological Approach to
Detecting Peptide Hormones.
Peptide 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 may
have been stored in the brain for a long period of time.
play no role in the functioning of the brain.
have been produced in some part of the body other than the brain.
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 to
reject the theory that peptide hormones are made by endocrine
glands.
revise their beliefs about the ability of antiserums to detect peptide
hormones.
invent techniques that would allow them to locate accurately brain
cells that produce peptide hormones.
develop a theory that account for the role 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?
It cannot be used to detect the presence of growth regulators in the
brain.
It cannot distinguish between the peptide hormones and substances that
are very similar to them.
It uses antiserums that are unable to cross the blood-brain
barrier.
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 with
incredulity.
derision.
indifference.
enthusiasm.
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