题干

某多肽有20个氨基酸,其中天冬氨酸4个,分别位于第5、6、15、20位(如图所示);肽酶X专门作用于天冬氨酸羧基端的肽键,肽酶Y专门作用于天冬氨酸氨基端的肽键,下列相关叙述正确的是(   )

A:该20肽含有的肽键至少为20个

B:该20肽游离的氨基和羧基至少各为1个和4个

C:肽酶Y完全作用后产生的多肽共含有氨基酸19个

D:肽酶X完全作用后产生的多肽中氧原子数目比20肽少了1个

上一题 下一题 0.0难度 选择题 更新时间:2019-03-09 11:10:09

答案(点此获取答案解析)

D

同类题2

阅读下面短文,掌握其大意,从短文后各题所给的四个选项A、B、C、D中,选出可以填入空白处的最佳选项。

      He met her at a party. She was outstanding; many guys were after her, but 1 paid any attention to him. After the party, he invited her for coffee. She was surprised. So as not to appear rude, she went 2.

      As they sat in a nice coffee shop, he was too nervous3say anything and she felt uncomfortable. 4, he asked the waiter, "Could you please give me some salt? I'd like to put it in my coffee."

     They stared at him. He turned red, but when the 5 came, he put it in his coffee and drank. Curious, she asked, "6 put salt in the coffee?" He explained, "When I was a little 7, I lived near the sea. I liked playing on the seaside ... I could feel its taste salty, like salty coffee. Now every time I drink it, I 8my childhood and my hometown. I miss it and my parents, 9are still there."

      She was deeply 10. That was the start to their love story.So they married and lived happily together.11 forty years, he passed away and left her a letter which said:My dearest, please forgive(原谅) my life-long 12. Remember the first time we dated? I was so nervous I asked for salt 13sugar. It was hard for me to ask for a change, so I just went ahead. Sweetheart, I don't exactly like salty 14. But as it mattered so much to you, I've learnt to enjoy it. If I could live a 15 time, I hope we can be together again, even if it means that I have to drink salty coffee for the rest of my life.