问题 单项选择题 A1/A2型题

体内许多酶的活性与其分子中半胱氨酸残基上的巯基直接有关,有些毒物能与酶分子的巯基结合而抑制酶活性。下列物质中,能保护酶分子上的巯基的是()。

A.胱氨酸

B.蛋氨酸

C.二价阳离子

D.还原型谷胱甘肽

E.硫酸铵

答案

参考答案:D

解析:谷胱甘肽(GSH)是一种不典型的三肽,谷氨酸通过γ-羧基与半胱氨酸的α-氨基形成肽键,故称γ-谷胱甘肽。它通过功能基团巯基参与细胞的氧化还原作用,清除氧化剂,具有保护某些蛋白质的活性巯基不被氧化的作用。

选择题
阅读理解

阅读理解。

     When I wake up on summer mornings, I know I am going to my favorite place to volunteer and make

a difference in someone's life just by being with him or her-a summer school for autistic (患孤独症的)

children.

     By helping the kids read or do math, I am not only teaching important skills but also helping them feel

like any other kid. There are many wrong ideas about autism. The kids I work with can think and feel.

They need help only in certain areas.

     Of course, each kid is special. For example, some kids like to draw, and others like to sing.

     At the school, the kids learn through about 20 activities. These activities can help them learn skills they

will need later in life.

     The very first day I volunteered, a boy came up to me, put his hand on my shoulder, and said "Hello."

From then on, I knew I could make a difference.

     Another boy loved to have me read books that can help him learn to read. Sometimes he could be

encouraged to read a few words or sentences. Finally, one day during reading practice, he read nearly 220

words himself!

     Summer school is also a time for fun. Last summer, bagpipe (风笛) players came to perform. Most of

us had our hands over our ears because they were so loud. When they asked for a volunteer from the

audience, one girl raised her hand as high as she could, got up on stage, and even tried the bagpipes in front

of everyone.

     Through these experiences, I realize that the challenges these kids face do not stop them from doing

many amazing things. I'm teaching them, but they are teaching me more.

1. According to Paragraph 2, many people think autistic kids _____.

A. can't read or do math

B. don't have important skills

C. don't play with other kids

D. can't think or feel

2. The author believed he could make a difference when _____.

A. a boy greeted him actively

B. a boy let him read books

C. a boy could read by himself

D. a girl tried the bagpipes

3. The phrase "these experiences" in the last paragraph refers to the following EXCEPT _____.

A. "I" read the books for kids

B. a boy read nearly 220 words himself

C. a girl tried the bagpipes on stage as a volunteer

D. a boy said hello to "me" politely

4. What does the author mainly talk about in the passage?

A. His teaching experience in a summer holiday.

B. How to make a difference in others' lives.

C. His experience as a volunteer in a special summer school.

D. Autistic children's hard life.