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 .
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 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.
上一篇: 考研英语阅读篇章二十几岁要明白生活的不易
下一篇: 考研英语阅读真题文章三十篇之三
科学家发现删除痛苦记忆的新方法
体坛英语资讯:Chinas U-22 team defeat Indonesia 2-0 at Chongqing International Football Tournament
大学英语六级YouTheme纲核心难词A
国内英语资讯:China to improve capital fund management of fixed-asset investment projects
大学英语六级YouTheme纲核心难词B
体坛英语资讯:Mozambique arrive in Kenya for friendly match
国内英语资讯:Chinese president arrives in Brazil for BRICS summit
国际英语资讯:Tariffs threaten nearly 1.5 mln U.S. jobs: Port of Los Angeles
国际英语资讯:Spotlight: Greece sees increasing Chinese visitors amid closer ties
英语四级考试迫在眉睫词汇复习势在必行4
2019年12月大学英语四级作文范文:职业选择
The Stars I Admire 我敬佩的明星
国内英语资讯:Chinese, Greek presidents visit Acropolis Museum
词汇六级四十天突破—讲义与笔记12
国际英语资讯:U.S. House holds first public hearing in Trump impeachment inquiry
国内英语资讯:China urges U.S. to stop pushing Hong Kong-related bills
非谓语动词的一般式及完成式
国内英语资讯:China refutes U.S., U.K. remarks on Hong Kong violence
国际英语资讯:Experts hail China-Brazil satellite program as model for BRICS sci-tech endeavors
麦当劳巨无霸汉堡酱,现在单独卖了
国际英语资讯:Egyptian FM, UN envoy discuss ways to resolve Libyan crisis
国际英语资讯:Trump blames Feds policy for capping economic, stock market gains
词汇六级四十天突破—讲义与笔记7
国内英语资讯:China unveils outline for strengthening patriotic education
H&M推出人狗同款毛衣!
体坛英语资讯:Djokovic beaten by Tsitsipas in Shanghai Masters quarterfinals
Under Armour财务状况遭受调查,股价大跌
词汇六级四十天突破—讲义与笔记10
国际英语资讯:UN-backed fund earmarks 39 mln USD to tackle climate change impact in Nepal
词汇六级四十天突破—讲义与笔记4