2011考研：歷年真題來源報刊閱讀50篇連載(2)

　　2. A matter of life and death

　　(The Economists, Jan 23rd, 2006)

　　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 little-known puzzle. There are thousands of reverse-transcriptase 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 transcriptase-producing 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 cancer-cell genes that produced reverse transcriptase, and likewise found the tumours grew more slowly.

　　Moreover, both the drugs and the gene-silencing 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 anti-HIV 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.

　　1. According to the first paragraph, cancer cells and newly fertilized eggs are similar to each other in the following aspects except that .

　　A. both of them copy their contents and divide quickly

　　B. both of them genetic information of organisms

　　C. both of their division involves genetic reprogramming

　　D. both of them contain reverse transcriptase

　　2. Reverse transcriptase can .

　　A. recreate DNA’s cousin RNA B. make the cell’s protein publishing line work

　　C. flatten some cancer cells D. recreate DNA

　　3. What is the most important achievement of Corrado Spadafora’s experients?

　　A. Reverse transcriptase is necessary for embryos to develop.

　　B. Getting rid of reverse transcriptase’s effects change the cells.

　　C. Common anti-HIV drugs are effective to cure cancer.

　　D. A more precise mechanism is suggested to promote the healthier immune systems.

　　4. The word “them” (line 2, paragrapg 5) refer to .

　　A. cancer cells B. reverse transcriptase C. the enzyme D. healthy embryos

　　5. How can we slow the growth of tumors?

　　A. create more reverse transcriptase B. use nevirapine as late as possible

　　C. silence the cancer-cell genes D. promote cells dividing

　　考研詞匯

　　molecular

　　a.分子的,由分子組成的

　　[真題例句] But NBAC members are planning to word the recommendation narrowly to avoid new restrictions on research that involves the cloning of human DNA or cells-routine in molecular biology.[1999年閱讀4]

　　[例句精譯] 但是,NBAC成員們正計劃在建議的措辭上更為嚴謹,以避免給克隆人體DNA或細胞等研究帶來更多地限制——(這屬于)分子生物研究中的常規(guī)課題。

　　reverse

　　n.①相反,反轉(zhuǎn),顛倒;②背面,后面;a.相反的,倒轉(zhuǎn)的;v.顛倒,倒轉(zhuǎn),(使)倒退

　　[真題例句] Anyone can see this trend is unsustainable.Yet few seem willing to try to reverse (v.) it.[2003年閱讀4]

　　[例句精譯] 任何人都明白這個趨勢不能維持下去,但是很少有人愿意扭轉(zhuǎn)它。

　　expose

　　v.①(to)使暴露,受到;②使曝光;③揭露

　　[真題例句] (73) Owing to the remarkable development in mass-communications, 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年翻譯]

　　[例句精譯] (73)大眾通訊的顯著發(fā)展使各地的人們不斷感到有新的需求,不斷接觸到新的習俗和思想,由于上述原因,政府常常得推出更多的革新。

　　juvenile

　　a.青少年的,幼稚的;n.青少年,少年讀物

　　[真題例句] 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]

　　[例句精譯] 有關(guān)少年犯罪的許多理論往往將其主要原因歸咎于個人或社會.

　　immune

　　a.①免疫的,有免疫力的;②有受影響的;③免除的,豁免的

　　[真題例句] The rats (49：develop) bacterial infections of the blood , (50：as if) their immune (①) systems—the self-protecting mechanism against disease—had crashed.[1995年完形]

　　[例句精譯] 老鼠患血液細菌感染,似乎它們的免疫系統(tǒng)——抵御疾病的自我保護機制——已崩潰。

　　precise

　　a.精確的,準確的

　　[真題例句] 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年閱讀5]

　　[例句精譯] 很多用來描述貨幣政策的詞,如“引導經(jīng)濟軟著陸”,“經(jīng)濟剎車”,使貨幣政策聽起來像是一門精確的科學。

　　背景知識介紹

　　反轉(zhuǎn)錄酶的發(fā)現(xiàn)

　　1970年Temin等在致癌RNA病毒中發(fā)現(xiàn)了一種特殊的DNA聚合酶,該酶以RNA為核板,根據(jù)堿基配對原則,按照RNA的核苷酸順序(其中V與A配對)合成DNA。這一過程與一般遺傳信息流轉(zhuǎn)錄的方向相反,故稱為反轉(zhuǎn)錄,催化此過程的DNA聚合酶叫做反轉(zhuǎn)錄酶(reverse transcriptase)。后來發(fā)現(xiàn)反轉(zhuǎn)錄酶不僅普遍存在于RNA病毒中,哺乳動物的胚胎細胞和正在分裂的淋巴細胞中也有反轉(zhuǎn)錄酶。

　　反轉(zhuǎn)錄酶的發(fā)現(xiàn)對于遺傳工程技術(shù)起了很大的推動作用,目前它已成為一種重要的工具酶。用組織細胞提取mRNA并以它為模板,在反轉(zhuǎn)錄酶的作用下,合成出互補的DNA (cDNA),由此可構(gòu)建出cDNA文庫 (cDNA library),從中篩選特異的目的基因,這是在基因工程技術(shù)中比較常用的獲得目的基因的方法。

　　參考譯文

　　生和死的問題

　　懷孕與癌癥,前者是生命的開端,后者是生命的結(jié)束,但這兩者在分子程度的細節(jié)上卻有著相同之處。癌細胞復制自身并且快速分裂;新受精的卵細胞也一樣。兩者都要求基因的重組。令人好奇的是,作為重組的結(jié)果,這兩者都包含一種為數(shù)不少的生物酶——反轉(zhuǎn)錄酶,生物學家通常將這種酶與某些病毒性感染聯(lián)系在一起,包括HIV。反轉(zhuǎn)錄酶使部分細胞的蛋白質(zhì)鏈反向工作,反向復制和DNA類似但較不穩(wěn)定且相對而言并不重要的分子RNA,重新生成DNA——一種典型的儲存了生物基本遺傳信息的分子。為什么癌癥和胚胎有這些相同點仍然是一個謎。

　　羅馬意大利國家健康學院的Corrado Spadafora就在研究這個鮮為人知的難題。在所有哺乳動物的基因組中有上千個反轉(zhuǎn)錄酶的基因。Spadafora博士不敢肯定到底該做什么工作,但是他在利茲英國男科學會年會上提交的資料指出了某些答案。

　　Spadafora博士比較近表示反轉(zhuǎn)錄酶在老鼠胚胎的發(fā)育中是必需的。他用兩種方法除去反轉(zhuǎn)錄酶。第一種方法,他對在皮氏培養(yǎng)皿中生成的胚胎使用一種名為奈韋拉平的普通抗艾滋藥物時,這種藥物能破壞這種生物酶。在胚胎只有四個細胞的時候加入這種藥物會停止細胞繼續(xù)發(fā)育。如果晚一點、在胚胎分裂為8個細胞時加入藥物則沒有用。第二種方法,他使用藥物以一種沒有其他副作用的不明方法來專門抑制反轉(zhuǎn)錄酶基因的產(chǎn)生。效果是一樣的：胚胎并沒有死去,另外,在這個敏感的時期,他們似乎停留在了這個不成熟的階段。

　　有線索顯示,在早期假如胚胎想要實行將細胞轉(zhuǎn)化為不同種類的組織的功能,反轉(zhuǎn)錄酶是必需的。在Spadafora博士測試的10個基因中,有7個基因在健康的胚胎中是活動的,但在加入了奈韋拉平的胚胎中則沒有活動。

　　因為癌細胞同樣含有許多反轉(zhuǎn)錄酶,Spadafora博士很想知道是否停止這種生物酶的作用同樣會阻止細胞分裂。他將四種人類癌細胞移植到四組老鼠的體內(nèi),每一組用奈韋拉平或其他類似的藥來治療。在所有的試驗中,越早給藥腫瘤長得越慢,而且總是比沒有用藥的老鼠體內(nèi)的腫瘤長得慢。而在胚胎試驗中,他抑制了產(chǎn)生反轉(zhuǎn)錄酶的癌細胞的基因,同樣發(fā)現(xiàn)腫瘤的生長變慢了。

　　而且,無論是藥物還是通過基因沉默技術(shù)抑制致癌細胞,都說明去除反轉(zhuǎn)錄酶會導致細胞內(nèi)部分子結(jié)構(gòu)變化。

　　人們早就知道普通的抗艾滋病藥物可以減緩艾滋病人的癌細胞生長。而醫(yī)學界已經(jīng)開始利用這一實際情況研究提高免疫系統(tǒng)的藥物了。Spadafora博士的研究結(jié)果提供了更為具體的方法。

　　答案及解析

　　1.細節(jié)事實題【正確答案】B

　　根據(jù)文章第一段，DNA而非癌細胞和新受精卵細胞儲存生物的基本遺傳信息。

　　2.細節(jié)事實題【正確答案】D

　　第一段倒數(shù)第二句Reverse transcriptase makes ..., recreating DNA, ...明確指出反轉(zhuǎn)錄酶可以重新生成DNA。

　　3.推理題【正確答案】D

　　A和B僅是Corrado Spadafora的個別實驗的結(jié)果，由文章比較后一段可知C錯誤，D才是他所有研究的目的及比較大成就。

　　4.指代題【正確答案】A

　　第五段第一句中enzyme指reverse transcriptase，停止反轉(zhuǎn)錄酶可以阻止癌細胞分裂。

　　5.推理題【正確答案】C

　　由第五段可知，use nevirapine early 和silence the cancer�瞔ell genes是減慢腫瘤生長的兩種方法，僅C符合。