首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Dolly was once an awfully lonely sheep. When the famous cloned (of an exact copy of a plant or animal made by taking a cell from
Dolly was once an awfully lonely sheep. When the famous cloned (of an exact copy of a plant or animal made by taking a cell from
admin
2009-03-21
53
问题
Dolly was once an awfully lonely sheep. When the famous cloned (of an exact copy of a plant or animal made by taking a cell from it and developing it artificially) animal made headlinesin 1997, she was the only mammal ever to be manufactured from the cell of an adult donor. Since then, the clone ranks have swelled, with mice and cattle also making their way out of the labs. Last week cloning technology took another step forward when an international biotechnology company announced that it had created a litter of five genetically identical piglets (young pigs), and that it had a pretty good idea of how they could one day be used as organ donors for ailing humans.
The idea of turning pigs into
tissue factories
has been around for at least 30 years. Pigs breed easily and mature quickly, and their organs are roughly the same size.as those of humans, meaning operations can be performed with a relative snap-out, snap-in simplicity. The problem is, once the donor organ is stitched in place, the body rebels, rejecting it even more violently than it would a human transplant. " A pig heart transplanted in a person would turn black within minutes, " says David Ayares, a research director with PPL Therapeutics, the biotech firm that helped clone Dolly and also produced the piglets.
What causes pig organs to be rejected so quickly is a sugar molecule on the surface of pig cells that identifies the tissue as unmistakably nonhuman. When the immune system spots this marker, it calls out its defenses. PPL scientists recently succeeded in finding the gene responsible for the sugar and knocking it out of the nucleus of a pig cell. Their next step would be to extract that nucleus, insert it into a pig ovum, and then into the womb of a host pig. The sugar free piglet that was eventually born could then be cloned over and over as a source of safe transplant organs. The idea is to arrive at the ideal animal and repeatedly copy it exactly as it is. The cloned piglets PPL introduced to the world last week were created in just this way, though for this first experiment in pig replication the scientists left the sugar genes intact.
Despite this recent success, PPL is not likely to be setting up its organ shop anytime soon. Knocking out the key sugar gene solves only the problem of short-term rejection. Much more has to be done before any solution to long-term rejection can be found. Nonetheless, Ayares is optimistic, insisting that pig organs could be available in as little as five years. For the present, even a little new transplant material is a big improvement over what’s available, and for gravely ill patients awaiting a donor, that’s no small thing.
PPL scientists will try to solve their problem by
选项
A、removing the sugar molecule on the surface of pig cells.
B、distinguishing human tissues form those of pigs.
C、using the sugar-free nucleus in cloning a pig.
D、taking out the sugar genes from the cell of a pig.
答案
C
解析
根据第三段第三句“PPL scientists recently succeeded in finding the gene responsible for the sugar and knocking it out of the nucleus of a pig cell.”可知,与这些糖分子相关的基因存在于猪的细胞核,而不是细胞表面,故A选项错误;B选项的观点文中没有涉及;根据第三段第三句、第四句“PPL scientists recently…the gene responsible for the sugar and knocking it out of the nucleus of a pig cell.Their next step…into the womb of a host pig.”可知,PPL的科学家想用不含糖的细胞核克隆猪,以解决他们的问题,故正确答案为C选项;D选项只是解决该问题过程当中的一个步骤,不能完全解决问题,故不选。
转载请注明原文地址:https://kaotiyun.com/show/b8Pd777K
本试题收录于:
公共英语四级笔试题库公共英语(PETS)分类
0
公共英语四级笔试
公共英语(PETS)
相关试题推荐
Inathree-monthperiodlastyear,twoBrooklyniteshadtobecutoutoftheirapartmentsandcarriedtohospitalonstretchers
"Themoregadgetsthereare,the【31】______thingsseemtoget."saidHonoreErvin,co-authorofTheEtiquetteGirls:ThingsYou
Impatiencecharacterizesyoungintellectualworkers.Theywanttomaketheirmark【31】______.Soit’simportanttoget【32】______t
Somemoderncitiesareusuallyfamousforpeoplewholiveaverylongtime.
Beforeabigexam,asoundnight’ssleepwilldoyoubetterthanporingovertextbooks.That,atleast,isthefolkwisdom.And
Besidesthefunctionsasavitalentertainmentmedium,whatelsecanpeopleuseaTVas?
Besidesthefunctionsasavitalentertainmentmedium,whatelsecanpeopleuseaTVas?
Earthquakescanbedevastating【1】disasters.TheinfamousSanFranciscoearthquakeof1906causedover$200millionworthofdam
Earthquakescanbedevastating【1】disasters.TheinfamousSanFranciscoearthquakeof1906causedover$200millionworthofdam
part-time
随机试题
宪法的基本原则是指人们在制定和实施宪法过程中必须遵循的最基本的准则。在我国宪法的基本原则中,标志着中国特色社会主义最本质特征的是【】
正常粪便检查不正常的是
手术区皮肤消毒的范围最少距手术切口()
某药物加硝酸银试液产生黑色沉淀,此药物是
徐某是某人民法院的法官,下列有关他的说法错误的是哪项?
初始权属调查资料的归档时,文件袋封面应注明()等内容,以便于保管使用。
X企业2010年按税法规定可开支业务招待费20000元,全年实际开支60000元,当年按会计核算原则计算的税前会计利润为3000000万元,所得税税率为25%,假定无其他纳税调整因素,不存在任何暂时性差异影响,则下列各项中正确的是()。
以下关于商用房贷款的额度,说法正确的是()
(2014年)甲公司应收乙公司货款2000万元,因乙公司财务困难到期未予偿付,甲公司就该项债权计提了400万元的坏账准备。20×3年6月10日,双方签订协议,约定以乙公司生产的100件A产品抵偿该债务。乙公司A产品售价为13万元/件(不合增值税),成本为1
已知一个口袋里有5个红球,6个白球,7个黑球,则至少取出多少个球才能保证有一个红球和一个白球?
最新回复
(
0
)