2016考研英语阅读暑期训练：理学类(8)

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暑期集训来了，如何在暑期两个月创造出双倍的价值是每个考生想要达到的目标。这就
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    　　2016考研英语阅读暑期训练：理学类(8)
    The basic workings of DNA and RNA are no mystery. It's now well known that
DNA consists of four nucleotide “bases” (A， T， C and G)， whose linear sequences
(AATAGGCTCC……) encode hereditary information. Genes——discrete segments of long
DNA molecules——transcribe their sequences onto single-strand messenger RNA
molecules， which then serve as templates for proteins. In short， DNA makes
messenger RNA， and messenger RNA makes proteins. The production of a particular
protein is the goal of each gene. This 50-year-old insight is the bedrock of
modern biology， but science has not fully solved a related mystery. If every
cell in an organism contains the same full complement of genes， why are the
cells themselves so varied? How do different genes get turned on (“expressed”)
or off (“silenced”) in just the right combinations to produce heart cells， bone
cells and brain cells?
    That's where microRNA enters the picture. In the early 1990s， researchers
studying a species of worm discovered genes for a very short and very unusual
piece of RNA. Instead of synthesizing proteins， this tiny RNA molecule latched
onto messenger RNAs (chart)， causing their destruction. Without messenger RNA，
no protein was produced. In effect， the gene for that protein had been silenced.
The discovery was initially dismissed as an oddity in a worm， but scientists
have since found genes for hundreds of microRNAs in various plants and
animals——200 in humans alone. Many of these genes have survived in identical
forms in different species， indicating that they are essential to life. What，
exactly， is their role? We now suspect that by silencing particular genes at
just the right times——a process called RNA interference——they push genetically
identical cells down different paths of development， enabling some to digest
food while others perceive light.
    RNA interference gives researchers a new tool for understanding how living
things grow——how a plant assumes a particular shape， for example， or how a
baby's hand forms during gestation. Moreover， because microRNAs are so small and
simple in structure， they can be manufactured for use as research tools. If
scientists suspect that a particular gene is responsible for a disease， they can
design microRNA to silence the gene in affected laboratory animals. If the
disease is prevented or cured， the gene becomes a target for treatment.
    RNA interference has yet to generate new medicines， but if the technique
fulfills its promise， it could help us treat everything from viral infections to
cancer. MicroRNAs could be used to seal off human cells from disease-causing
viruses， or to disable viruses that gain entry. In a recent test-tube study，
researchers showed that RNA interference could make cells impermeable to HIV.
Early studies suggest that microRNAs can also boost the production of stem cells
in culture. By blocking production of growth-promoting proteins， microRNAs may
even help contain cancer cells.
    It is one thing to manipulate cells in a test tube， quite another to treat
people. Getting microRNAs safely into the right cells in the body will be
complicated. No one has yet attempted a human experiment. Even so， a field that
was just a curiosity in 1993 is now poised to change the world——all because we
invested in basic research. The scientists who discovered microRNAs were not
trying to prevent AIDS， grow stem cells or treat cancer. They just wanted to
figure out how something happened in a worm. As Buckminster Fuller observed，
“Development is programmable; discovery is not.”
    注(1)：本文选自Newsweek; 12/8/2003， p96-96， 1p， 1 diagram， 1c;
    注(2)：本文习题命题模仿对象2004年真题Text 3;
    　　1. The expression “silenced”(Line 5， Paragraph 2) most probably means
_________.
    [A]ruined
    [B]destroyed
    [C]killed
    [D]stopped
    　　2. How does the author feel about the study of MicroRNA?
    [A]Optimistic.
    [B]Confused.
    [C]Frightening.
    [D]Shocking.
    　　3. When mentioning “It is one thing to manipulate cells in a test tube，
quite another to treat people.”(Line 1， Paragraph 5)， the author implies that
__________.
    [A]the test of cells and the treatment of people are unrelated to each
other
    [B]the treatment of people is more complex than the cells in the
laboratory
    [C]more emphasis should be laid on the human tests
    [D]human treatment may not be successful
    　　4. What does Buckminster Fuller mean by “Development is programmable;
discovery is not.”(Last Line， Last Paragraph)?
    [A]Discovery is always made beyond one‘s expectation.
    [B]Development is easier than discovery.
    [C]Development lacks curiosity while discovery does not.
    [D]Development is less important than discovery.
    　　5.Which of the following is not true about RNA interference?
    [A]It prevents disease-causing viruses from entering human body.
    [B]It improves the production of stem cells.
    [C]It can cure of all kinds of human diseases.
    [D]It silences certain protein to prevent tumor.
    　　答案：DABAC