四级辅导：英语四级阅读（3）

　　NASA-Funded Research Discovers Life Built With Toxic Chemical

　　NASA-funded astrobiology research has changed the fundamental knowledge about what comprises all known life on Earth.

　　Researchers conducting tests in the harsh environment of Mono Lake in California have discovered the first known microorganism on Earth able to thrive and reproduce using the toxic chemical arsenic. The microorganism substitutes arsenic for phosphorus in its cell components.

　　The definition of life has just expanded， said Ed Weiler， NASAs associate administrator for the Science Mission Directorate at the agencys Headquarters in Washington. As we pursue our efforts to seek signs of life in the solar system， we have to think more broadly， more diversely and consider life as we do not know it.

　　This finding of an alternative biochemistry makeup will alter biology textbooks and expand the scope of the search for life beyond Earth. The research is published in this weeks edition of Science Express.

　　Carbon， hydrogen， nitrogen， oxygen， phosphorus and sulfur are the six basic building blocks of all known forms of life on Earth. Phosphorus is part of the chemical backbone of DNA and RNA， the structures that carry genetic instructions for life， and is considered an essential element for all living cells.

　　Phosphorus is a central component of the energy-carrying molecule in all cells （adenosine triphosphate） and also the phospholipids that form all cell membranes. Arsenic， which is chemically similar to phosphorus， is poisonous for most life on Earth. Arsenic disrupts metabolic pathways because chemically it behaves similarly to phosphate.

　　We know that some microbes can breathe arsenic， but what weve found is a microbe doing something new building parts of itself out of arsenic， said Felisa Wolfe-Simon， a NASA Astrobiology Research Fellow in residence at the U.S. Geological Survey in Menlo Park， Calif.， and the research teams lead scientist. If something here on Earth can do something so unexpected， what else can life do that we havent seen yet？

　　The newly discovered microbe， strain GFAJ-1， is a member of a common group of bacteria， the Gammaproteobacteria. In the laboratory， the researchers successfully grew microbes from the lake on a diet that was very lean on phosphorus， but included generous helpings of arsenic. When researchers removed the phosphorus and replaced it with arsenic the microbes continued to grow. Subsequent analyses indicated that the arsenic was being used to produce the building blocks of new GFAJ-1 cells.

　　The key issue the researchers investigated was when the microbe was grown on arsenic did the arsenic actually became incorporated into the organisms vital biochemical machinery， such as DNA， proteins and the cell membranes. A variety of sophisticated laboratory techniques was used to determine where the arsenic was incorporated.

　　The team chose to explore Mono Lake because of its unusual chemistry， especially its high salinity， high alkalinity， and high levels of arsenic. This chemistry is in part a result of Mono Lakes isolation from its sources of fresh water for 50 years.

　　The results of this study will inform ongoing research in many areas， including the study of Earths evolution， organic chemistry， biogeochemical cycles， disease mitigation and Earth system research. These findings also will open up new frontiers in microbiology and other areas of research.

　　The idea of alternative biochemistries for life is common in science fiction， said Carl Pilcher， director of the NASA Astrobiology Institute at the agencys Ames Research Center in Moffett Field， Calif. Until now a life form using arsenic as a building block was only theoretical， but now we know such life exists in Mono Lake.

　　The research team included scientists from the U.S. Geological Survey， Arizona State University in Tempe， Ariz.， Lawrence Livermore National Laboratory in Livermore， Calif.， Duquesne University in Pittsburgh， Penn.， and the Stanford Synchroton Radiation Lightsource in Menlo Park， Calif.

　　NASAs Astrobiology Program in Washington contributed funding for the research through its Exobiology and Evolutionary Biology program and the NASA Astrobiology Institute. NASAs Astrobiology Program supports research into the origin， evolution， distribution， and future of life on Earth.

　　「内容简介」

　　文章第一段以一句话简洁宣布美国宇航局有了科学新发现。

　　接着，文章描述了美国宇航局这项发现的意义。

　　然后，文章也介绍了已知生命的六大基本构建元素，而这次新发现的细菌的成分如何。详细解释了为什么这是一项全新发现，并引用了美国宇航局研究员的话语告诉我们这项微生物的不同之处以及生命的未知神奇。

　　最后，文章详细介绍了这次发现的微生物以及该研究成果将来的应用领域。

　　「词汇短语讲解」

　　①comprise vt. 包括，组成，构成 与comprise同样表示组成、构成的词还有compose、consist等词，在用法上有一些区别。

　　comprise是及物动词，后面不需要加介词；consist则后面要加介词of，通常指一个整体由几部分构成，或由某些材料构成；compose则一般使用be composed of这种被动形式。

　　②一些必背常用单词，harsh adj. 严酷的，刺耳的 conduct v. 引导，带领，管理，指挥 substitute n. 替代物质；代用品 v. 取代，替代。

　　③expand，extend，expend和prolong.这几个词，特别是前面三个，看起来很像，但意思却有些差别。

　　expand是膨胀、扩大的意思，既可指体积等的扩大，也可用于指野心、欲望的膨胀。

　　extend 扩展、延伸的意思，是长度或范围的扩展、延伸。 extend ones business 扩大营业 extend ones congratulations to 向祝贺

　　expend是花费的意思，expensive就是从它演变而来的。

　　prolong 通常表示时间的延长。

　　④in residence 住在某处的 这里引申为属于某机构的。

　　⑤in part 部分地

　　⑥building block 积木，基础部分

　　「快速阅读支招」

　　科学类文章因为涉及科学研究，有很多生物化学名词，我们在阅读中不必纠结于这么多专有名词，关键是弄清楚文章意思，了解一些常用词。在阅读文章前要先扫视一遍问题，带着问题去读，不然这么长篇幅的文章里可能最后都会因为烦躁而读不下去。

　　另外，这类文章中，通常有很多长句，包括从句、倒装、强调等语法运用。我们在阅读时要尝试自己划分主要成分，根据这些主干部分了解句子意思。