问题 问答题 简答题

PCR技术的基本原理

答案

参考答案:

该技术是在模板DNA、引物和四种脱氧核糖核苷酸存在下,依赖于DNA聚合酶的酶促合成反应。

DNA聚合酶以单链DNA为模板,借助一小段双链DNA来启动合成,通过一个或两个人工合成的寡核苷酸引物与单链DNA模板中的一段互补序列结合,形成部分双链。

在适宜的温度和环境下,DNA聚合酶将脱氧单核苷酸加到引物3´-OH末端,并以此为起始点,沿模板5´→3´方向延伸,合成一条新的DNA互补链

阅读理解

Reading is a task that we all do either for enjoyment or education, but sometimes the book we have to read may lack the attraction. Here are some tips on avoiding getting bored while reading.

Try to step into the world of literature(文学) you are reading. __56___ If the wind is blowing, imagine how the leaves move with each movement of air.

Make your reading area unlike your sleeping area. If you sleep with the radio on, then shut it off. __57__ Make the area you read in an area that feels almost uncomfortable to sleep in. This will keep you from becoming sleepy.

__58__ If you are reading for a book report , then take breaks from time to time to put what you are reading into some kind of context(语境) that you can put into the report.

Take a break once in a while. __59___ You’d better offer yourself short breaks while reading in case you are too tired, which may make you give up.

Find a friend. ___60__ Try to read the same book. Even if you read different books, you can tell him or her how good the book is. Also, a friend can encourage you to read.

A.Get a note book and make notes.

B.Put aside sometime and devote it just to reading.

C.Reading can be more enjoyable when you do it with a friend.

D.Some books are a little too boring for “hours on end” reading.E. Don’t just read the words on the page; picture them in your mind.

F. Determine what you are supposed to get from the reading material.

G. If you don’t like lights on when you are asleep, then turn on the lights.

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