以含有CAA重复序列的人工合成多核苷酸链为模板，在无细胞蛋白质_爱下问搜题

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问题单项选择题 A2型题

以含有CAA重复序列的人工合成多核苷酸链为模板，在无细胞蛋白质合成体系中能合成3种多肽：多聚谷氨酰胺、多聚天冬酰胺、多聚苏氨酸，已知谷氨酰胺和天冬酰胺的密码子分别为CAA和AAC，则苏氨酸的密码子为（）

A.CCA

B.ACC

C.CAC

D.ACA

E.AAA

答案

参考答案：D

解析：遗传密码子的破译是20世纪60年代利用化学合成的核苷酸聚合物，特别是重复序列中的三联体作为模板，在体外合成肽链而完成的。CAA重复序列依从不同起始点开始可组合成3种三联体重复序列，分别是CAA、AAC、ACA，因为CAA和AAC分别是谷氨酰胺和天冬酰胺的密码子，故选D。

完形填空

完形填空。

     When leaming new vocabulary, don't just memorize a list of words.   1   ,try to make five sentences
using each new word.Tben use the new words as    2    as you can when you leam it.This way you will
remember new words for a long time.
     Practicing sounds,you know,is    3   一take the"th"sound for example.Choose words that begin   4   "th"and repeat them over and over agam   5    you are comfortable with them.Let's by!This,that,those,them,
think,thought,thmugh,thin,thick一．
     Read,read,read in English,of course!Reading is one of the best ways to increase your Vocabulary and
   6  your grammar in a natural and fun waV.  Be sure to choose topics or books you are inte ested．7         When someone is talking in Engish,   8     for the main point.If you hear a word you don't understand,
ignore(忽略)it and go on listening.If you think about the word,you will    9   everything else the person is
saying.Always remembe 10    makes perect．

( )1.A.Instead
( )2.A.often
( )3.A.diffrent
( )4.A.at
( )5.A.after
( )6.A.make progress
( )7.A.at
( )8.A.1isten
( )9.A.wihout
( )10.A.practice

B.But
B.always
B.easy
B.with
B.before
B.achieve
B.on
B.hear
B.10se
B.to practice

C.Instead of
C.sometimes
C.diffcult
C.of
C.until
C.enlarge
C.in
C.100k
C.miss
C.speak

D.While
D.never
D.hardly
D.on
D.when
D.improve
D.of
D.care
D.get
D.speaking

判断题

水蒸气流速设计时一般为50～10m/s。