题干

降钙素是一种多肽类激素,临床上用于治疗骨质疏松症等.人的降钙素活性很低,半衰期较短.某科学机构为了研发一种活性高、半衰期长的新型降钙素,从预期新型降钙素的功能出发,推测相应的脱氧核苷酸序列,并人工合成了两条72个碱基的DNA单链,两条链通过18个碱基对形成部分双链DNA片段,再利用Klenow酶补平,获得双链DNA,过程如图:

下列有关分析错误的是(  )

A:Klenow酶是一种DNA聚合酶

B:合成的双链DNA有72个碱基对

C:EcoRⅠ和BamHⅠ双酶切的目的是保证目的基因和运载体的定向连接

D:筛选重组质粒需要大肠杆菌质粒中含有标记基因

上一题 下一题 0.0难度 选择题 更新时间:2018-08-12 06:31:41

答案(点此获取答案解析)

B

同类题2

阅读理解

    The kids in a village in Ethiopia wear dirty, ragged clothes. They sleep beside cows and sheep in huts made of sticks and mud. They have no school. Yet they all can chant the English alphabet, and some can make words.

    The key to their success: 20 tablet computers(平板电脑) dropped off in their Ethiopian village in February by a U.S. group called One Laptop Per Child.

The goal is to find out whether kids using today's new technology can teach themselves to read in places where there are no schools or teachers. The Massachusetts Institute of Technology researchers analyzing the project data say they're already amazed. “What I think has already happened is that the kids have already learned more than they would have in one year of kindergarten,” said Matt Keller, who runs the Ethiopia program.

    The fastest learner—and the first to turn on one of the tablets—is 8-year-old Kelbesa Negusse. The device's camera was disabled to save memory, yet within weeks Kelbesa had figured out its workings and made the camera work. He called himself a lion, a marker of accomplishment in Ethiopia.

With his tablet, Kelbasa rearranged the letters HSROE into one of the many English animal names he knows. Then he spelled words on his own. “Seven months ago he didn't know any English. That's unbelievable,” said Keller.

    The project aims to get kids to a stage called “deep reading,” where they can read to learn. It won't be in Amharic, Ethiopia's first language, but in English, which is widely seen as the ticket to higher paying jobs.