问题 问答题

什么是快速扩增cDNA末端技术(RACE)?

答案

参考答案:

RACE是一项基于已知cDNA序列快速克隆5’或3’端缺失序列的技术。方法大致是先获取RNA,去掉mRNA 5’端帽子,加上寡聚接头,逆转录后,以寡聚接头的部分序列和3’端反向引物进行PCR扩增,获5’端序列;3’RACE以5’端基因特异引物和3’端寡聚dT下游部分序列为引物进行PCR扩增获得3’端序列。RACE除用于全长cDNA获取外,还被用于识别5’和3’端非转录序列,研究启动子区的保守性等。

阅读理解

阅读理解。

     Washington D.C. is the capital of the United States. It's the center of national government. It's a busy, working city with a large population. But what is more, Washington is also a city of history and culture. It is

  home to many famous and interesting public buildings and monuments, many of which are connected with

  the federal government.    

     Washington was created in 1790, when Congress (the highest lawmaking body of the United States)

  decided to place the nation's new capital in the east of the country. It was built half way between the

 northern and southern states of America. And of course it was named after George Washington, the first

 President of the United States.

     There are many tourist sights in Washington. Perhaps the most important tourist sight is the Capital

 Building. This is the house of the Congress. Another world-famous building in Washington is the White

 House. This is the home and office of the President of the United States. Most visitors are, however,

  surprised by how small the White House actually is.

     Washington is also a great cultural city. The Library of Congress contains one of the largest library

  collections in the world. The Smithsonian Museum holds the nation's largest collection of cultural

 materials. And the John F. Kennedy Center is a famous center of art and culture. It has many great

 musical and theatre performances throughout the year.

1. From the passage we know that Washington is situated in _____.

    A. the east, on the middle point from north to south of the country

    B. the center of the U. S. A.

    C. the east of the U. S. A.

    D. the east and halfway away from the north

2. The passage mentions _____ buildings.

    A. six    

    B. five  

    C. four      

    D. three

3. The writer introduces Washington in order of _____.

    A. population, history and culture  

    B. history and culture

    C. general introduction, history, sights and culture

    D. general introduction, history, sights, buildings and culture

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