问题 单项选择题

关于酶活性中心的叙述,正确的是( )。

A.酶原有能发挥催化作用的活性中心
B.由一级结构上相互邻近的氨基酸组成
C.必需基团存在的唯一部位
D.均由亲水氨基酸组成
E.含结合基团和催化基团

答案

参考答案:E

解析: 酶分子中能与底物结合并发生催化作用的局部空间结构称为酶的活性中心。活性中心中有许多与催化作用直接相关的基团,称为必需基团。有些必需基团涉及酶与底物的结合,又称为结合基团,有些具有催化功能,称为催化基团。在酶活性中心外,也存在一些与活性相关的必需基团,它对维持酶分子应有构象是必需的。

阅读理解

When I was a boy, I was a football fan. I played football with some other boys in the backyard all the time. My mom was worried that I would get ill in the hot summer.

One day my brother gave me a new football. I came into the yard and played it excitedly. But suddenly, the ball flew through the window and nearly hit my dad. Dad said nothing. He took my football and cut it in half.

I didn’t cry because I knew how terrible my mistake was. I didn’t expect (期待) to get another football. But to my surprise, Dad bought me another one the next month and told me to be more careful. I was really thankful for my father’s forgiveness (宽恕). He showed me that even when I made a mistake, he still loved me and gave me another chance.

Parents always give us their unconditional (无条件的) love and forgiveness. We should always give our love and forgiveness to them, too.

小题1:The writer played football in the backyard all the time because ________.

A.he was easy to get ill

B.he was a football fan

C.his father was a football player

D.his mother was worried about him小题2:How did the writer feel when he got the football from his brother?

A.Sad.

B.Worried.

C.Terrible.

D.Excited.小题3:The writer didn’t cry because ________.

A.he knew his mistake

B.his father cut the football in half

C.his father was very happy

D.he nearly hit his father小题4:After his father bought him another football, the writer ________.

A.forgot his mistake

B.was angry

C.was thankful to his father

D.didn’t like it小题5:What can we learn from the story?

A.We should learn to play football.

B.We should love and forgive our parents.

C.We shouldn’t make mistakes.

D.We must play football with our parents.

单项选择题