科学家破译30亿年前的化石基因
文章来源:未知 文章作者:meng 发布时间:2010-12-20 02:01 字体: [ ]  进入论坛
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About 580 million years ago, life on Earth began a rapid period of change called the Cambrian(寒武纪) Explosion, a period defined by the birth of new life forms over many millions of years that ultimately helped bring about the modern diversity of animals. Fossils help palaeontologists chronicle(记录) the evolution of life since then, but drawing a picture of life during the 3 billion years that preceded(领先) the Cambrian Period is challenging, because the soft-bodied Precambrian cells rarely left fossil imprints1. However, those early life forms did leave behind one abundant microscopic2 fossil: DNA3. Because all living organisms inherit their genomes from ancestral genomes, computational biologists at MIT reasoned that they could use modern-day genomes to reconstruct the evolution of ancient microbes. They combined information from the ever-growing genome library with their own mathematical model that takes into account the ways that genes5 evolve: new gene4 families can be born and inherited; genes can be swapped6 or horizontally(水平地) transferred between organisms; genes can be duplicated in the same genome; and genes can be lost.

The scientists traced thousands of genes from 100 modern genomes back to those genes' first appearance on Earth to create a genomic fossil telling not only when genes came into being but also which ancient microbes possessed7 those genes. The work suggests that the collective genome of all life underwent an expansion between 3.3 and 2.8 billion years ago, during which time 27 percent of all presently existing gene families came into being.

Eric Alm, a professor in the Department of Civil and Environmental Engineering and the Department of Biological Engineering, and Lawrence David, who recently received his Ph.D. from MIT and is now a Junior Fellow in the Harvard Society of Fellows, have named this period the Archean Expansion.

Because so many of the new genes they identified are related to oxygen, Alm and David first thought that the emergence8 of oxygen might be responsible for the Archean Expansion. Oxygen did not exist in the Earth's atmosphere until about 2.5 billion years ago when it began to accumulate, likely killing9 off vast numbers of anerobic(厌氧的) life forms in the Great Oxidation Event.

"The Great Oxidation Event was probably the most catastrophic event in the history of cellular10 life, but we don't have any biological record of it," says Alm.

Closer inspection11, however, showed that oxygen-utilizing genes didn't appear until the tail end of the Archean Expansion 2.8 billion years ago, which is more consistent with the date geochemists assign to the Great Oxidation Event.

Instead, Alm and David believe they've detected the birth of modern electron transport, the biochemical process responsible for shuttling electrons within cellular membranes12. Electron transport is used to breathe oxygen and by plants and some microbes during photosynthesis13 when they harvest energy directly from the sun. A form of photosynthesis called oxygenic photosynthesis is believed to be responsible for generating the oxygen associated with the Great Oxidation Event, and is responsible for the oxygen we breathe today.

The evolution of electron transport during the Archean Expansion would have enabled several key stages in the history of life, including photosynthesis(光合作用) and respiration14(呼吸) , both of which could lead to much larger amounts of energy being harvested and stored in the biosphere15(生物圈) .

"Our results can't say if the development of electron transport directly caused the Archean Expansion," says David. "Nonetheless, we can speculate that having access to a much larger energy budget enabled the biosphere to host larger and more complex microbial ecosystems16."

David and Alm also went on to investigate how microbial genomes evolved after the Archean Expansion by looking at the metals and molecules17 associated with the genes and how those changed in abundance over time. They found an increasing percentage of genes using oxygen, and enzymes18 associated with copper19 and molybdenum(钼) , which is consistent with the geological record of evolution.

"What is really remarkable20 about these findings is that they prove that the histories of very ancient events are recorded in the shared DNA of living organisms," says Alm. "And now that we are beginning to understand how to decode21 that history, I have hope that we can reconstruct some of the earliest events in the evolution of life in great detail."



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1 imprints def38b53bdddb921bca90a8e2d0cad78     
n.压印( imprint的名词复数 );痕迹;持久影响
参考例句:
  • With each step he took, his boots left muddy imprints on the floor. 她父亲的毡靴一移动,就在地板上压了几个泥圈圈。 来自汉英文学 - 中国现代小说
  • In Freudian theory, the imprints are memories, albeit unconscious ones. 在佛洛伊德理论中,这些痕迹就是记忆,只不过它们是无意识的。 来自互联网
2 microscopic nDrxq     
adj.微小的,细微的,极小的,显微的
参考例句:
  • It's impossible to read his microscopic handwriting.不可能看清他那极小的书写字迹。
  • A plant's lungs are the microscopic pores in its leaves.植物的肺就是其叶片上微细的气孔。
3 DNA 4u3z1l     
(缩)deoxyribonucleic acid 脱氧核糖核酸
参考例句:
  • DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
  • Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。
4 gene WgKxx     
n.遗传因子,基因
参考例句:
  • A single gene may have many effects.单一基因可能具有很多种效应。
  • The targeting of gene therapy has been paid close attention.其中基因治疗的靶向性是值得密切关注的问题之一。
5 genes 01914f8eac35d7e14afa065217edd8c0     
n.基因( gene的名词复数 )
参考例句:
  • You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因,所以能够活得很长。 来自《简明英汉词典》
  • Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪
6 swapped 3982604ac592befc46570aef4e827102     
交换(工作)( swap的过去式和过去分词 ); 用…替换,把…换成,掉换(过来)
参考例句:
  • I liked her coat and she liked mine, so we swapped. 我喜欢她的外套,她喜欢我的外套,于是我们就交换了。
  • At half-time the manager swapped some of the players around. 经理在半场时把几名队员换下了场。
7 possessed xuyyQ     
adj.疯狂的;拥有的,占有的
参考例句:
  • He flew out of the room like a man possessed.他像着了魔似地猛然冲出房门。
  • He behaved like someone possessed.他行为举止像是魔怔了。
8 emergence 5p3xr     
n.浮现,显现,出现,(植物)突出体
参考例句:
  • The last decade saw the emergence of a dynamic economy.最近10年见证了经济增长的姿态。
  • Language emerges and develops with the emergence and development of society.语言是随着社会的产生而产生,随着社会的发展而发展的。
9 killing kpBziQ     
n.巨额利润;突然赚大钱,发大财
参考例句:
  • Investors are set to make a killing from the sell-off.投资者准备清仓以便大赚一笔。
  • Last week my brother made a killing on Wall Street.上个周我兄弟在华尔街赚了一大笔。
10 cellular aU1yo     
adj.移动的;细胞的,由细胞组成的
参考例句:
  • She has a cellular telephone in her car.她的汽车里有一部无线通讯电话机。
  • Many people use cellular materials as sensitive elements in hygrometers.很多人用蜂窝状的材料作为测量温度的传感元件。
11 inspection y6TxG     
n.检查,审查,检阅
参考例句:
  • On random inspection the meat was found to be bad.经抽查,发现肉变质了。
  • The soldiers lined up for their daily inspection by their officers.士兵们列队接受军官的日常检阅。
12 membranes 93ec26b8b1eb155ef0aeaa845da95972     
n.(动物或植物体内的)薄膜( membrane的名词复数 );隔膜;(可起防水、防风等作用的)膜状物
参考例句:
  • The waste material is placed in cells with permeable membranes. 废液置于有渗透膜的槽中。 来自辞典例句
  • The sarcoplasmic reticulum is a system of intracellular membranes. 肌浆网属于细胞内膜系统。 来自辞典例句
13 photosynthesis A2Czp     
n.光合作用
参考例句:
  • In apple trees photosynthesis occurs almost exclusively in the leaves.苹果树的光合作用几乎只发生在叶内。
  • Chloroplasts are the structures in which photosynthesis happens.叶绿体就是光合作用发生的地方。
14 respiration us7yt     
n.呼吸作用;一次呼吸;植物光合作用
参考例句:
  • They tried artificial respiration but it was of no avail.他们试做人工呼吸,可是无效。
  • They made frequent checks on his respiration,pulse and blood.他们经常检查他的呼吸、脉搏和血液。
15 biosphere 5Ryyu     
n.生命层,生物圈
参考例句:
  • The entire biosphere was becoming more transparent.整个生物圈越来越透明。
  • The impact of modern technology on the biosphere is evident worldwide.现代技术对生物圈的影响在全世界是明显的。
16 ecosystems 94cb0e40a815bea1157ac8aab9a5380d     
n.生态系统( ecosystem的名词复数 )
参考例句:
  • There are highly sensitive and delicately balanced ecosystems in the forest. 森林里有高度敏感、灵敏平衡的各种生态系统。 来自《简明英汉词典》
  • Madagascar's ecosystems range from rainforest to semi-desert. 马达加斯加生态系统类型多样,从雨林到半荒漠等不一而足。 来自辞典例句
17 molecules 187c25e49d45ad10b2f266c1fa7a8d49     
分子( molecule的名词复数 )
参考例句:
  • The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
  • Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里,大分子裂变为小分子。
18 enzymes 7881ad8ce9c83424f7874e70266ed2d8     
n. 酶,酵素
参考例句:
  • It was said that washing powders containing enzymes remove stains more efficiently. 据说加酶洗衣粉除污更有效。
  • Among the enzymes which are particularly effective are pepsin, papain. 在酶当中特别有效的是胃朊酶、木瓜酶。
19 copper HZXyU     
n.铜;铜币;铜器;adj.铜(制)的;(紫)铜色的
参考例句:
  • The students are asked to prove the purity of copper.要求学生们检验铜的纯度。
  • Copper is a good medium for the conduction of heat and electricity.铜是热和电的良导体。
20 remarkable 8Vbx6     
adj.显著的,异常的,非凡的,值得注意的
参考例句:
  • She has made remarkable headway in her writing skills.她在写作技巧方面有了长足进步。
  • These cars are remarkable for the quietness of their engines.这些汽车因发动机没有噪音而不同凡响。
21 decode WxYxg     
vt.译(码),解(码)
参考例句:
  • All he had to do was decode it and pass it over.他需要做的就是将它破译然后转给他人。
  • The secret documents were intercepted and decoded.机密文件遭截获并被破译。
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