问题 单项选择题 B型题

阻碍DNA合成的药物()

A.紫杉醇

B.顺铂

C.氟尿嘧啶

D.三尖杉酯碱

E.放线菌素D

答案

参考答案:C

解析:氟尿嘧啶主要作用在体内经活化途径生成的5-氟尿嘧啶脱氧核苷酸与胸腺酸合成酶的活性中心共价结合,抑制此酶的活性,使脱氧核苷酸缺乏,DNA合成阻碍;顺铂的氯可被水取代,形成活泼的带正电的水化分子,然后与DNA反应,从而抑制DNA复制和转录;紫杉醇主要作用于聚合态微管,抑制微管解聚化而使之稳定,从而阻碍细胞有丝分裂;三尖杉酯碱抑制真核细胞蛋白质合成的起始阶段,使多聚核糖体分解,抑制有丝分裂。

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完形填空。
     Imagine you receive an e-mail that looks something like this: ARE YOU GOING TO CLASS TODAY?
How does  1  this message make you feel?  2  did the sender use all capital letters? Was he or she angry,
or did that person just  3  to turn off the "Caps Lock (大写的)" on the computer? This e-mail "sounds" like
the  4  is shouting because using all capital letters in an e-mail is usually the way that people shout  5 .
     Knowing when and where not to use capital letters is just one  6  of online manners. Don't do anything
on line that you wouldn't do in  7  life. Don't use information that  8  else has written, and  9  it's yours. Do
share your knowledge of the  10  with others.
( )1. A. leaving  
( )2. A. Why      
( )3. A. want     
( )4. A. worker   
( )5. A. at home  
( )6. A. mistake  
( )7. A. digital  
( )8. A. no one   
( )9. A. speak    
(     )10. A. Internet
B. copying
B. How    
B. begin  
B. writer 
B. on line
B. advice 
B. modern 
B. someone
B. tell   
B. book   
C. watching   
C. What       
C. forget     
C. reader     
C. at strangers
C. example    
C. real       
C. everyone   
C. talk       
C. e-mail     
D. reading     
D. When        
D. remember    
D. receiver    
D. in the street
D. joke        
D. healthy                                             
D. anyone      
D. say         
D. school      
单项选择题