[ti:Scientists Building Redesigned Life Forms] [by:www.51voa.com] [00:00.00]更多听力请访问51VOA.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51VOA.COM