From Genes to GMOs
Today, genes can be isolated, identified, and cloned, then inserted into other organisms to alter their traits. The process is called genetic engineering. For this technology to develop, a few tools were necessary. In the 1970s, scientists isolated bacterial plasmids. These are hula-hoop-shaped double-stranded units of DNA that can be moved easily from one cell to another. They also discovered "scissors," called restriction enzymes for cutting the DNA into predictable, reproducible patterns. These enzymes are used to"snip apart" plasmids at very specific DNA sequences, leaving free ends that can be rejoined as the scientist chooses. Restriction enzymes occur in bacteria as part of a natural defense mechanism to guard against invading viruses. Many different types are now available, each cutting DNA at a different sequence of base pairs.
Once a plasmid is snipped open, a foreign piece of DNA, cut by the same enzyme scissors, can be taped, end to end, into the plasmid using another enzyme, DNA ligase. This is the glue that sticks all the pieces together. The new plasmid is inserted back into a cell, where numerous copies can be made. Introduction of specific genetic material into rapidly reproducing target bacteria can turn the cells into miniature factories for production of useful substances. For example, when the Exxon Valdez oil freighter ran aground in 1989 and spilled thirty-eight million liters of oil, oil-eating bacteria, created in just this manner, were used in the cleanup operation. The oil was broken down five times faster with help from the genetically modified organisms (GMOs).
Plasmid technology has also been developed for moving targeted genetic material into plants. In this technique, scientists use the plasmid from a bacterium that causes tumors on plants. In nature, this bacterium transfers genetic material into plant tissues by releasing plasmids onto damaged plant cells. The plasmids enter the plant tissue and produce a swelling, or tumor. Because of this special ability to invade plant tissue, these tumor-inducing (TI) plasmids are now used routinely as "taxi cabs" to carry target genes into a wide variety of plant cells, including, for example, corn. The European corn borer is a common pest in this economically valuable crop. When pesticides are used against them, timing is critical. If sprayed too late, the corn borer will already have made a home inside the corn stem and will not be killed. CIBA Research was the first company to develop what has become commonly known as Bt corn. It contains genes that allow it to resist infestation by the corn borer. The Bt genes came from a bacterium called Bacillus thuring ensis. It produces a protein called Bt protoxin. When an insect larva eats these bacteria, the toxin contained in the bacterium attaches to the insect's gut and makes holes in it, and the larva starves to death. Bt corn can be grown using less pesticide, and sometimes even no pesticide.
考研詞匯：
isolate[ˈaisəleit]
v.隔離，孤立
[真題例句] Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots.[1998年閱讀5]
[例句精譯] 地球上散落分布著100多個(gè)相互獨(dú)立的小火山活動(dòng)區(qū)，地質(zhì)學(xué)家稱之為熱點(diǎn)。
trait[treit]
n.特征，特點(diǎn)，特性
[真題例句] (61) One difficulty is that almost all of what is called behavioral science continues to trace behavior to states of mind, feelings, traits of character, human nature, and so on.[2002年翻譯]
[例句精譯] (61)難題之一在于所謂的行為科學(xué)幾乎全都依然從心態(tài)、情感、性格特征、人性等方面去尋找行為的根源。 spill[spil]
v.溢出，濺出;n.摔下，跌下
[真題例句] 54. What the author tries to suggest may best be interpreted as_______.[1998年閱讀1]
[A] It’s no use crying over spilt (v.) milk
[例句精譯] 54. 作者試圖提醒的意思可以最恰當(dāng)?shù)亟忉尀椋篲___。
[A] "覆水難收"
modify[ˈmɔdifai]
v.更改，修改，修飾
[真題例句] In response, schools are modifying their programs, adapting instruction to children who are exceptional, to those who cannot profit substantially from regular programs.[1994年閱讀3]
[例句精譯] 作為回應(yīng)，學(xué)校也在調(diào)整課程安排，使授課能夠適應(yīng)特殊兒童，適應(yīng)那些不能從常規(guī)課程中真正獲益的兒童的需要。
routine[ru:ˈti:n]
n.例行公事，常規(guī);a.常規(guī)的，例行的
[真題例句] You can make a mental blueprint of a desire as you would make a blueprint of a house, and each of us is continually making these blueprints in the general routine (n.) of everyday living.[1996年閱讀1]
[例句精譯] 你可以在頭腦里勾畫出一幅欲望的藍(lán)圖，就像你可以設(shè)計(jì)房屋的藍(lán)圖一樣，而我們每個(gè)人在日常生活中都在不停地畫著這樣的藍(lán)圖。
[真題例句] Like other human beings, he encounters moral issues even in everyday performance of his routine (a.) duties-he is not supposed to cook his experiments, manufacture evidence, or doctor his reports. [2006年翻譯]
[例句精譯] 像其他人類一樣，普通科學(xué)家甚至在每天日常的工作中都遭遇到了道義上的問題--他不應(yīng)該偽造實(shí)驗(yàn)、制造證據(jù)或改動(dòng)他的報(bào)告。
infestation[infes’teiʃən]
n.(害蟲, 盜賊等)群襲, 出沒, 橫行
背景常識介紹：
基因工程是生物工程的一個(gè)重要分支，它與細(xì)胞工程、酶工程、蛋白質(zhì)工程和微生物工程共同組成了生物工程。 所謂基因工程(genetic engineering)是在分子水平上對基因進(jìn)行操作的復(fù)雜技術(shù)，是將外源基因通過體外重組后導(dǎo)入受體細(xì)胞內(nèi)，使這個(gè)基因能在受體細(xì)胞內(nèi)復(fù)制、轉(zhuǎn)錄、翻譯表達(dá)的操作。它是用人為的方法將所需要的某一供體生物的遺傳物質(zhì)--DNA大分子提取出來，在離體條件下用適當(dāng)?shù)墓ぞ呙高M(jìn)行切割后，把它與作為載體的DNA分子連接起來，然后與載體一起導(dǎo)入某一更易生長、繁殖的受體細(xì)胞中，以讓外源物質(zhì)在其中"安家落戶"，進(jìn)行正常的復(fù)制和表達(dá)，從而獲得新物種的一種嶄新技術(shù)。
參考譯文：
從基因到轉(zhuǎn)基因生命體
如今，基因可以被分離、識別和克隆，并且，將基因插入其他生命體中還能改變它們的特征，這一過程叫基因工程。要發(fā)展這種技術(shù)，我們需要一些工具。20世紀(jì)70年代，科學(xué)家分離出了細(xì)菌的原生質(zhì)。它們是形似呼拉圈的雙股DNA單位，可以被輕易地從一個(gè)細(xì)胞轉(zhuǎn)移到另一個(gè)細(xì)胞�？茖W(xué)家們還發(fā)現(xiàn)了被稱為限制酶的"剪刀"，可以把DNA分裂成可以預(yù)測和可以復(fù)制的形式。這些酶被用來把特定的DNA序列中的原生質(zhì)切斷，切斷后的原生質(zhì)可以被科學(xué)家們自由地重新連接。作為抵抗病毒的自然防御機(jī)制的一部分，限制酶存在于細(xì)菌中。現(xiàn)在科學(xué)家們已經(jīng)發(fā)現(xiàn)了許多種限制酶，它們可以將不同序列的DNA切斷。
一旦原生質(zhì)被分開后，用同樣限制酶剪開的外來DNA片段和它的被切斷的端口被粘到一起，形成了新的原生質(zhì)。連接時(shí)使用的是另一種酶--DNA連接酶。這種連接酶可以把所有的碎片粘到一起。新的原生質(zhì)被插回細(xì)胞中，在那里可以進(jìn)行多次復(fù)制。如果把特定的基因材料引入高速復(fù)制的目標(biāo)細(xì)菌中，細(xì)胞就會(huì)變成生產(chǎn)有用物質(zhì)的微型工廠。例如，當(dāng)�？松镜耐郀柕掀澨栍洼喸�1989年擱淺后，它泄露了3800萬公升的油。用上述方法創(chuàng)造出的吃油的細(xì)菌曾被用于清理油污的行動(dòng)。有了轉(zhuǎn)基因生命體(GMOs)的幫助，油分解的速度提高了五倍。
細(xì)胞質(zhì)技術(shù)還被應(yīng)用于把目標(biāo)基因材料轉(zhuǎn)移到植物的過程中。在應(yīng)用這種技術(shù)時(shí)，科學(xué)家們使用導(dǎo)致植物腫瘤的細(xì)菌中的原生質(zhì)。通過把原生質(zhì)釋放到損壞的植物細(xì)胞上，這種細(xì)菌把基因材料轉(zhuǎn)移到植物的組織當(dāng)中。原生質(zhì)進(jìn)入植物組織后產(chǎn)生了浮腫，或者說是腫瘤。因?yàn)榫哂羞@種特殊的侵襲植物組織的能力，這些導(dǎo)致腫瘤的(TI)原生質(zhì)被人們習(xí)慣地當(dāng)成"出租車"來使用，目的是把目標(biāo)基因帶到多種植物細(xì)胞當(dāng)中，比如說，玉米細(xì)胞。歐洲玉米螟普遍存在于玉米這種經(jīng)濟(jì)價(jià)值很高的農(nóng)作物當(dāng)中。使用殺蟲劑消滅這種害蟲時(shí)，時(shí)機(jī)的掌握很關(guān)鍵。如果殺蟲劑噴灑得太晚，玉米螟早已經(jīng)在玉米莖的內(nèi)部安家了。這樣，它們就不能被殺死。CIBA研究所是第一家研制出我們通常所稱的Bt玉米的公司。這種玉米中含有能夠抵御玉米螟的基因。這種Bt基因來自于一種名為圖根菌的細(xì)菌。它會(huì)產(chǎn)生Bt原霉素的蛋白質(zhì)。當(dāng)昆蟲的幼蟲吃了這些細(xì)菌后，細(xì)菌中的霉素就會(huì)附著在昆蟲的內(nèi)臟，并在上面打出許多洞。這樣，幼蟲就會(huì)被餓死。Bt玉米在生長過程中需要很少，甚至不需要?dú)⑾x劑�！�
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