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.

考研词汇：

isolate［ˈaisəleit］
v.隔离，孤立

［真题例句］ Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots.［1998年阅读5］
［例句精译］ 地球上散落分布着100多个相互独立的小火山活动区，地质学家称之为热点。

trait［treit］
n.特征，特点，特性

［真题例句］ (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年翻译］
［例句精译］ (61)难题之一在于所谓的行为科学几乎全都依然从心态、情感、性格特征、人性等方面去寻找行为的根源。

spill［spil］
v.溢出，溅出；n.摔下，跌下

［真题例句］ 54. What the author tries to suggest may best be interpreted as_______.［1998年阅读1］
［A］ It's no use crying over spilt (v.) milk
［例句精译］ 54. 作者试图提醒的意思可以最恰当地解释为：____。
［A］ "覆水难收"

modify［ˈmɔdifai］
v.更改，修改，修饰

［真题例句］ In response, schools are modifying their programs, adapting instruction to children who are exceptional, to those who cannot profit substantially from regular programs.［1994年阅读3］
［例句精译］ 作为回应，学校也在调整课程安排，使授课能够适应特殊儿童，适应那些不能从常规课程中真正获益的儿童的需要。

routine［ru:ˈti:n］
n.例行公事，常规；a.常规的，例行的

［真题例句］ 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年阅读1］
［例句精译］ 你可以在头脑里勾画出一幅欲望的蓝图，就像你可以设计房屋的蓝图一样，而我们每个人在日常生活中都在不停地画着这样的蓝图。
［真题例句］ 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年翻译］
［例句精译］ 像其他人类一样，普通科学家甚至在每天日常的工作中都遭遇到了道义上的问题--他不应该伪造实验、制造证据或改动他的报告。

infestation［infes'teiʃən］
n.(害虫, 盗贼等)群袭, 出没, 横行

背景常识介绍：

基因工程是生物工程的一个重要分支，它与细胞工程、酶工程、蛋白质工程和微生物工程共同组成了生物工程。
所谓基因工程（genetic engineering)是在分子水平上对基因进行操作的复杂技术，是将外源基因通过体外重组后导入受体细胞内，使这个基因能在受体细胞内复制、转录、翻译表达的操作。它是用人为的方法将所需要的某一供体生物的遗传物质--DNA大分子提取出来，在离体条件下用适当的工具酶进行切割后，把它与作为载体的DNA分子连接起来，然后与载体一起导入某一更易生长、繁殖的受体细胞中，以让外源物质在其中"安家落户"，进行正常的复制和表达，从而获得新物种的一种崭新技术。

参考译文：

从基因到转基因生命体
如今，基因可以被分离、识别和克隆，并且，将基因插入其他生命体中还能改变它们的特征，这一过程叫基因工程。要发展这种技术，我们需要一些工具。20世纪70年代，科学家分离出了细菌的原生质。它们是形似呼拉圈的双股DNA单位，可以被轻易地从一个细胞转移到另一个细胞。科学家们还发现了被称为限制酶的"剪刀"，可以把DNA分裂成可以预测和可以复制的形式。这些酶被用来把特定的DNA序列中的原生质切断，切断后的原生质可以被科学家们自由地重新连接。作为抵抗病毒的自然防御机制的一部分，限制酶存在于细菌中。现在科学家们已经发现了许多种限制酶，它们可以将不同序列的DNA切断。
一旦原生质被分开后，用同样限制酶剪开的外来DNA片段和它的被切断的端口被粘到一起，形成了新的原生质。连接时使用的是另一种酶--DNA连接酶。这种连接酶可以把所有的碎片粘到一起。新的原生质被插回细胞中，在那里可以进行多次复制。如果把特定的基因材料引入高速复制的目标细菌中，细胞就会变成生产有用物质的微型工厂。例如，当埃克森公司的瓦尔迪兹号油轮在1989年搁浅后，它泄露了3800万公升的油。用上述方法创造出的吃油的细菌曾被用于清理油污的行动。有了转基因生命体（GMOs）的帮助，油分解的速度提高了五倍。
细胞质技术还被应用于把目标基因材料转移到植物的过程中。在应用这种技术时，科学家们使用导致植物肿瘤的细菌中的原生质。通过把原生质释放到损坏的植物细胞上，这种细菌把基因材料转移到植物的组织当中。原生质进入植物组织后产生了浮肿，或者说是肿瘤。因为具有这种特殊的侵袭植物组织的能力，这些导致肿瘤的（TI）原生质被人们习惯地当成"出租车"来使用，目的是把目标基因带到多种植物细胞当中，比如说，玉米细胞。欧洲玉米螟普遍存在于玉米这种经济价值很高的农作物当中。使用杀虫剂消灭这种害虫时，时机的掌握很关键。如果杀虫剂喷洒得太晚，玉米螟早已经在玉米茎的内部安家了。这样，它们就不能被杀死。CIBA研究所是第一家研制出我们通常所称的Bt玉米的公司。这种玉米中含有能够抵御玉米螟的基因。这种Bt基因来自于一种名为图根菌的细菌。它会产生Bt原霉素的蛋白质。当昆虫的幼虫吃了这些细菌后，细菌中的霉素就会附着在昆虫的内脏，并在上面打出许多洞。这样，幼虫就会被饿死。Bt玉米在生长过程中需要很少，甚至不需要杀虫剂。