标题: 考研英语历年真题来源报刊阅读2 [打印本页] 作者: dorm99 时间: 2010-12-5 02:03 标题: 考研英语历年真题来源报刊阅读2 A matter of life and deathNO.2
2A matter of life and death
CONCEPTION and cancer, which mark the beginning and, often, the end of life, share some molecular details. Cancer cells copy their contents and divide rapidly; so do newly fertilized eggs. This requires genetic reprogramming. Curiously, as a result of the reprogramming, both contain appreciable amounts of an enzyme called reverse transcriptase that biologists more usually associate with certain viral infections, including HIV. Reverse transcriptase makes part of the cell’s protein publishing line work backwards, recreating DNA, a molecule in which organisms typically store genetic information, from its less stable and correspondingly less favoured cousin, RNA. Why it does so in cancer and in embryos, though, is something of a mystery.
Corrado Spadafora, of Italy’s National Institute of Health, in Rome, studies this littlenown puzzle. There are thousands of reverseranscriptase genes in the genomes of all mammals. What that job is exactly, Dr Spadafora is not sure, but data he presented at the annual meeting of the British Andrology Society, in Leeds, suggest some answers.
Dr Spadafora showed recently that reverse transcriptase is required for mouse embryos to develop. He did this by removing it in two ways. First, he exposed embryos created in Petri dishes to a common AIDS drug called nevirapine, which works by gumming the enzyme up. This halted development whenever it was added to embryos up to the stage when they were only four cells big. Adding the drug later, when the four cells had divided into eight, had no effect. Second, he checked the drug was not bad for the embryos in some other, unknown, way by specifically turning off reverse transcriptaseroducing genes. The result was the same: the embryos did not die, and again, during the sensitive period, they seemed to get stuck in a juvenile stage.
There are hints that reverse transcriptase is needed for a lot of early embryonic functions associated with getting cells ready to specialize into different types of tissue. Seven of the ten genes Dr Spadafora tested were active in healthy embryos, but were shut down in the nevirapine arrested ones.
Since cancer cells also contain a lot of reverse transcriptase, Dr Spadafora wondered whether stopping the enzyme working might stop them dividing as well. He transplanted four kinds of human cancer into four groups of mice and treated some of each group with nevirapine or a similar drug. In all cases the earlier he gave the drug, the slower the tumours grew, and they always grew more slowly than tumours in mice which got neither drug. As in the embryo experiments, he then silenced the cancerell genes that produced reverse transcriptase, and likewise found the tumours grew more slowly.
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Moreover, both the drugs and the geneilencing technique flattened some types of cancer cells, which suggests that both methods of getting rid of reverse transcriptase’s effects caused similar molecular changes inside the cells.
That common antiIV drugs slow cancer growth in AIDS patients has been known for some time. Doctors, however, have attributed the fact to the healthier immune systems the drugs promote. Dr Spadafora’s results suggest a more precise mechanism.
molecular［mEu5lekjulE］
a.分子的，由分子组成的
［真题例句］ But NBAC members are planning to word the recommendation narrowly to avoid new restrictions on research that involves the cloning of human DNA or cellsoutine in molecular biology.［1999年阅读4］
［真题例句］ Anyone can see this trend is unsustainable.Yet few seem willing to try to reverse (v.) it.［2003年阅读4］
［例句精译］ 任何人都明白这个趋势不能维持下去，但是很少有人愿意扭转它。
expose［iks5pEuz］
v.①（to）使暴露，受到；②使曝光；③揭露
［真题例句］ (73) Owing to the remarkable development in massommunications, people everywhere are feeling new wants and are being exposed (①) to new customs and ideas, while governments are often forced to introduce still further innovations for the reasons given above.［2000年翻译］
［真题例句］ Many theories concerning the causes of juvenile (a.) Delinquency (crimes committed by young people) focus either on the individual or on society as the major contributing influence.［2004年完形］
［例句精译］ 有关少年犯罪的许多理论往往将其主要原因归咎于个人或社会.
immune［i5mju:n］
a.①免疫的，有免疫力的；②不受影响的；③免除的，豁免的
［真题例句］ The rats (49：develop) bacterial infections of the blood , (50：as if) their immune (①) systems—the selfrotecting mechanism against disease—had crashed.［1995年完形］
［例句精译］ 老鼠患血液细菌感染，似乎它们的免疫系统——抵御疾病的自我保护机制——已崩溃。
precise［pri5sais］
a.精确的，准确的
［真题例句］ Much of the language used to describe monetary policy, such as “steering the economy to a soft landing” or “a touch on the brakes”, makes it sound like a precise science.［1997年阅读5］