搜题请搜索小程序“爱下问搜题”
问题 问答题 简答题

维生素C在胶原合成中有何作用？试从胶原代谢角度分析坏血病的产生机制。

答案

参考答案：

胶原合成时，多肽链中的脯氨酸和赖氨酸残基分别在脯氨酰羟化酶和赖氨酰羟化酶作用下羟化为羟脯氨酸和羟赖氨酸，成为胶原蛋白特有的两种氨基酸。维生素C是两种羟化酶的必需辅助因子，当维生素C缺乏时该酶活性降低，胶原合成障碍，导致毛细血管易于破裂，皮下、黏膜出血，牙齿松动，骨脆易折断，创口不易愈合等，此即为维生素C缺乏所致坏血病

完形填空
完形填空。
     The kiwi (鹬鸵) lives only in New Zealand. It is a very strange   1   because it cannot fly. The kiwi is
the same size   2   a chicken. It has no wings or tail. It does not have any feathers 1ike other birds. It has
hair on its body. Each   3   has four toes (脚趾). Its beak (喙) is very long.
     The kiwi likes a lot of trees around it. It sleeps in the daytime because the sunlight may  4     its eyes.
Its nose is very great. It can   5     things with it. It is the only bird in the world that can smell things. The
kiwi's eggs are very big.
     There are only   6   kiwis in New Zealand now. People     7     see them. The government says that
people cannot kill kiwis. New Zealanders want their kiwis   8   . There is a picture of kiwis   9     New
Zealand money. People from New Zealand are sometimes called   10   .
( )1.  A. animal   
( )2.  A. like  
( )3.  A. foot  
( )4.  A. hit    
( )5.  A. eat    
( )6.  A. a little  
( )7.  A. always
( )8.  A. to live
( )9.  A. at  
( )10. A. bird lovers		B. plant
B. likes
B. feet
B. hurt
B. drink
B. little
B. usually
B. to die
B. in
B. birds 		C. bird  
C. as    
C. nose  
C. kill  
C. smell
C. a few
C. seldom (很少)
C. to go away
C. on    
C. kiwis		D. tree          
D. from          
D. mouth        
D. protect      
D. carry        
D. few          
D. often        
D. to fly        
D. from          
D. English      
查看答案
单项选择题

对软包装且体积较小的物品，如洗发液、香烟等物品，可用（）的方法来判断。

A.嗅

B.捏

C.烧

D.敲
查看答案