问题 单项选择题 A1/A2型题

关于DNA连接酶的作用正确的是()

A.可催化dNTP的5′-磷酸与DNA链的3′-OH相连接

B.催化的反应在原核细胞中需要消耗ATP

C.在DNA复制、修复、重组和剪接中均起缝合缺口的作用

D.合成冈崎片段

E.连接两个单独存在的DNA单链

答案

参考答案:C

解析:DNA连接酶催化以氢键连接于模板DNA链上的两个相邻DNA片段通过磷酸二酯键相连接,但不能连接单独存在的DNA或RNA单链。反应消耗能量,在真核生物消耗ATP,在原核生物则消耗NAD+。

阅读理解

阅读下面短文,并根据短文后的要求答题。

      The relationship between students and teachers is less formal in the U.S. than in many other countries,

especially at college. (1)当老师走进教室时,学生不必起立。Students are encouraged to ask

questions during class, to go to the teacher’s office for help after class, and to phone if they can’t go to

school and need help with their lessons. (2)Most teachers allow students to enter class late or leave early,

if necessary.

     (3)However, students are still asked to be polite to their teacher and classmates and to be quiet during

a test. When students want to ask questions, they usually put up a hand and wait. When the teacher or a

student is speaking to the class, it’s rude to talk to another classmate, even in a low voice. When a test is

being given, talking to a classmate is not only rude but also wrong. In the eyes of most American teachers,

students who are talking to each other during a test are cheating.

1.将(1)句译成英文。

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2.将(2)句改为被动语态。

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3.将(3)句译成中文。

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4.从文中找出与所给句子意义相近的句子。

Most teachers think it is dishonest of students to talk about something when they are having an exam.

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5.写出文中最能表达该短文主题的句子。

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问答题