问题 问答题 简答题

什么是穿梭质粒载体,举例1个穿梭质粒载体

答案

参考答案:

定义:一类由人工构建的具有两种不同复制起点和选择标记、可在两种不同的宿主细胞中存活和复制的质粒载体。如:大肠杆菌-枯草芽孢杆菌穿梭质粒载体、大肠杆菌-酿酒酵母穿梭质粒载体、大肠杆菌-土壤农杆菌穿梭质粒载体(植物转化载体)、大肠杆菌-动物细胞穿梭质粒载体。pHT304是应用于苏云金芽胞杆菌的穿梭载体。

阅读理解

One summer vacation in my college, my roommate Ted asked to me to work on his father’s farm in Argentina. The idea was exciting. Then I had second thoughts. I had never been far from New England, and I had been homesick my first few weeks at college. What about the language? The more I thought about it, the more the idea worried me.

Finally, I turned down the invitation. Then I realized I had turned down something I wanted to do because I was scared and felt depressed(沮丧). That experience taught me a valuable lesson and I developed a rule for myself: do what makes you anxious(焦虑); don’t do what makes you depressed.

In my senior year, I wanted to be a writer. But my professor wanted me to teach. I hesitated. The idea of writing was much scarier than spending a summer in Argentina. Back and forth I went, making my decision, unmaking it. Suddenly I realized that every time I gave up the idea of writing, that downhearted feeling went through me.

Giving up writing really depressed me. Then I learned another lesson. To avoid the depression meant having to bear much worry and concern.

When I first began writing articles, I often interviewed big names. Before each interview I would get butterflies in the stomach. One of them was the great composer Duke Ellington. On the stage and on television, he seemed very confident. Then I learned Ellington still got stage fright(害怕). If Ellington still had anxiety attacks, how could I avoid them? I went on doing those frightening interviews. Little by little, I was even looking forward to the interviews. Where were those butterflies?

In truth, they were still there, but fewer of them. I had learned from a process psychologists(心理学家) call “extinction”. If you put an individual in an anxious situation often, finally there isn’t anything to be worried about, which brings me to a conclusion: you’ll never get rid of anxiety by avoiding the things that caused it.

The point is that the new, the different, is definitely scary. But each time you try something, you learn, and as the learning piles up, the world opens to you.

小题1:We can infer from the passage that the author________. 

A.finds it difficult to make decision

B.has found out what causes anxiety

C.was encouraged by Duke Ellington’s stage fright

D.no longer feels anxious about new experiences小题2:What does the word “extinction” in Paragraph 6 means?

A.a person’s loss of confidence little by little

B.the natural development of a child’s abilities

C.the inborn ability to avoid anxious situations

D.the process of losing fear by keeping facing anxiety小题3:Which of the following opinions does the writer probably accept?

A.Anxiety can be a positive drive

B.Hesitation leads to depression.

C.Avoiding anxiety reduces depression.

D.Depression is a signal that one is growing up.小题4:What's the best title for the passage?

A.Confidence: Key to Success

B.Anxiety: Challenge by Another Name

C.Depression: A Psychological Appearance

D.Success: A Trip Through Anxiety and Depression

选择题