[ti:Scientists Building Redesigned Life Forms]
[by:www.21voa.com]
[00:00.00]更多听力请访问21VOA.COM
[00:00.04]For thousands of years, humans have used yeast
[00:04.80]for making bread and alcoholic drinks, such as beer.
[00:10.44]But scientists are now constructing synthetic yeast
[00:15.56]that can do more than make a sandwich or a drink.
[00:20.13]The synthetic yeast can be used for medicines,
[00:25.32]vaccines, and biofuels – among other things.
[00:30.96]So, how does it work?
[00:33.60]Yeast, like humans, are living organisms with DNA.
[00:39.64]DNA is short for deoxyribonucleic acid.
[00:46.76]On long strings it carries the genetic instructions used in the growth,
[00:54.16]functioning and reproduction of all living things.
[01:00.84]Modern science allows researchers to cut
[01:04.60]and move around the four biological compounds that make up DNA.
[01:11.56]The compounds are known by the letters A,C, G and T.
[01:20.00]The yeast genome, or its genetic material map,
[01:25.20]has more than 10 million of these DNA letters.
[01:30.88]But that is nothing compared to us:
[01:34.44]Humans have about three billion.
[01:39.16]Scientists have long been able to make changes in the DNA code.
[01:45.44]But now, some scientists are doing something different.
[01:51.20]When you walk into Jef Boeke's lab it smells like bread rising.
[01:59.20]But his team is not making homemade dough.
[02:03.84]Instead, they are changing the order of genes in yeast cells.
[02:11.56]Boeke manages a team of 11 labs on four continents.
[02:18.12]He spoke to VOA Learning English about this project.
[02:24.12]"What we're doing basically is writing that DNA
[02:30.04]and we also modify it along the way,
[02:34.46]so we kind of redesign it on a computer,
[02:37.76]and then it's that modified DNA that we actually put into cells.
[02:43.62]We swap it in place of the DNA that's already there."
[02:48.44]So far, the scientists have constructed and replaced six of yeast's 16 chromosomes.
[02:58.52]The new chromosomes have all worked well.
[03:03.04]Yeast is already used to produce many other valuable compounds,
[03:08.76]such as medicines, vaccines and biofuels.
[03:14.20]By making synthetic yeast,
[03:17.13]researchers could make different combinations used for different jobs.
[03:24.08]For example, one combination may be better for making biofuel,
[03:30.02]and another for making medicine.
[03:33.88]These compounds could then be made in large, industrial amounts.
[03:40.68]Synthetic yeast could also be used to make bioplastic
[03:46.88]—a material that, unlike plastic made from petroleum, would be biodegradable.
[03:54.64]Using this material would help reduce pollution.
[04:00.28]Boeke says the possible uses for yeast are limited only by one's imagination.
[04:10.12]"They can be programmed through DNA writing to produce
[04:16.40]really an almost limitless range of products
[04:21.12]in terms of molecules or chemical compounds
[04:25.28]that that can replace things that we currently make from petroleum or
[04:32.00]other sources and as well as some new materials
[04:36.12]that don't even exist today."
[04:38.76]So far, scientists have engineered yeast to produce bright colors.
[04:45.44]The yeast can make artwork, and in the future,
[04:50.12]may even be used to paint a house.
[04:55.68]But, to be clear, Boeke says, his teams are not creating new life.
[05:05.04]"No one's ever created life out of non-living material.
[05:10.92]All the experiments we do start with pre-existing living cells
[05:16.24]and we introduced modified DNA into it
[05:20.32]so that's actually a common misunderstanding that we're creating life.
[05:26.04]We are not creating life."
[05:28.28]However, redesigning DNA worries some people.
[05:34.20]Laurie Zoloth is a bioethicist at Northwestern University.
[05:40.92]She told the Associated Press (AP) that she is concerned
[05:45.76]about making organisms with "properties we cannot fully know."
[05:51.15]She said the work would concern people who believe creating life
[05:58.08]from scratch would give humans power they should not have.
[06:04.80]"It is not only a science project," she wrote to AP.
[06:10.16]"It is an ethical and moral and theological proposal of significant proportions."
[06:19.72]Boeke says he does not think his team is doing anything dangerous.
[06:26.36]He says he and other scientists always look at the risks,
[06:31.96]especially when it comes to food safety, or when researchers engineer viruses.
[06:40.68]Boeke says safety regulations help people who want to work in those areas.
[06:48.40]Other researchers experimenting with DNA
[06:52.64]are waiting to see the results of this yeast work.
[06:57.96]June Medford is with the University of Colorado.
[07:03.24]"I paid very careful attention to when they say ‘here are the lessons learned,'
[07:08.48]because if they can't do it in a simple thing like yeast,
[07:11.07]I will never be able to do it in a plant."
[07:13.72]But Medford and other DNA researchers will have to wait.
[07:18.96]Boeke needs at least another year to finish his pioneering project.
[07:26.47]I'm Anne Ball. 更多听力请访问21VOA.COM
END OF TRACK. "END OF TRACK." The two men bowed. "Whoever was that person you were talking to?" she enquired, as soon as they stood together. The took of triumph faded from her eyes, she had grown worn and weary. The roses were wilting on the walls, the lights were mostly down now. Hetty, looking in to see if anything was wanted, found herself driven away almost fiercely. I only saw Master Jervie once when he called at tea time, The year 1747 was opened by measures of restriction. The House of Lords, offended at the publication of the proceedings of the trial of Lord Lovat, summoned the parties to their bar, committed them to prison, and refused to liberate them till they had pledged themselves not to repeat the offence, and had paid very heavy fees. The consequence of this was that the transactions of the Peers were almost entirely suppressed for nearly thirty years from this time, and we draw our knowledge of them chiefly from notes taken by Horace Walpole and Lord Chancellor Hardwicke. What is still more remarkable, the reports of the House of Commons, being taken by stealth, and on the merest sufferance, are of the most meagre kind, sometimes altogether wanting, and the speeches are given uniformly under fictitious names; for to have attributed to Pitt or Pelham their[112] speeches by name would have brought down on the printers the summary vengeance of the House. Many of the members complained bitterly of this breach of the privileges of Parliament, and of "being put into print by low fellows"; but Pelham had the sense to tolerate them, saying, "Let them alone; they make better speeches for us than we can make for ourselves." Altogether, the House of Commons exhibited the most deplorable aspect that can be conceived. The Ministry had pursued Walpole's system of buying up opponents by place, or pension, or secret service money, till there was no life left in the House. Ministers passed their measures without troubling themselves to say much in their behalf; and the opposition dwindled to Sir John Hinde Cotton, now dismissed from office, and a feeble remnant of Jacobites raised but miserable resistance. In vain the Prince of Wales and the secret instigations of Bolingbroke and Doddington stimulated the spirit of discontent; both Houses had degenerated into most silent and insignificant arenas of very commonplace business. "It certainly will be. Miss Widgeon," answered Maria, with strictly "company manners." "One who has never had a brother exposed to the constant dangers of army life can hardly understand how glad we all feel to have Si snatched from the very jaws of death and brung back to us." "Just plug at 'em as you would at a crow, and then go on your way whistlin'?" persisted Harry. "Hurroo!" echoed Hennessey; "that's the ticket." "Come forward, keeper," continued the baron, "and state how these arrows came into your hands!" "Yes." HoMEJULIA京香2018下载
ENTER NUMBET 0015zxhrke.com.cn
www.xwchain.com.cn
www.nmrgift.com.cn
www.xuanerte.com.cn
www.jintai.org.cn
roboticsgen.com.cn
www.selllcard.com.cn
www.chndcep.org.cn
www.borum.com.cn
tuodeng.com.cn