问题 单项选择题

在复制中维持模板处于单链状态并保护单链完整的蛋白是

A.DnaA蛋白
B.DnaB蛋白
C.DnaC蛋白
D.DnaG蛋白
E.SSB

答案

参考答案:E

解析:[考点] DNA复制的酶

[分析]: 在DNA-pol参与复制之前,首先起作用的起始物质有DnaA蛋白、DnaB蛋白、DnaC蛋白。DnaA蛋白辨认复制起始点,DnaC蛋白辅助解螺旋酶(DnaB蛋白)使其在DNA链上移动并打开双链,故 113题应选A。作为模板的DNA总是要处于单链状态,而DNA分子只要符合碱基配对又总会有形成双链的倾向,但细胞内存在 SSB(单链DNA结合蛋白),其作用是在复制中维持模板DNA处于单链状态并保护单链的完整,故114题应选E。

单项选择题
完形填空

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完型填空(共20小题;每小题1.5分,满分30分)

About two years ago while working downtown at our company’s headquarters I met a man. I’ll call him “Martin”. Martin was a short, middle-aged man with a glandular(内分泌) problem. He was fat, using a walking stick to help, and was painfully shy. Almost every morning I saw Martin on the elevator. We were usually the only people there, so I made __36   conversation as we __37_ to the 15th floor. I chatted with him about sometimes weather and sometimes about each other’s weekend.

About six months __38   our daily elevator chats, Martin came to my office and asked if I had a minute to chat. Though we worked on the same floor, I’m sure he had to __39   to find me. I invited him to sit down. He said, “I wanted to come and say __40  . The company has let me go. Today will be my last day.”

I didn’t know what to say. __41   I was too familiar with saying goodbye to co-workers, it was never __42  . Honestly, I usually avoid talking about the event because I felt __43   and at a loss for words. I told him I was __44   and asked if there was anything I could do. He said, “No, I’ll be fine, I just wanted to take the time to thank you.” I was now __45   . He explained that our daily talks had __46   a lot to him.

He thanked me not only for  __47   with him in the mornings, but for speaking directly to him and others on the elevator, and for telling him a quick joke in the crowded cafeteria. It seemed that __48   had ever been his friend before—or if so they were __49   to him in public.

He said he didn’t want to __50   much of my time, as he knew I was busy and he needed to __51   his personal things. He had tears in his eyes as he shook my hand and left.

I’ve never seen him since, but I imagine he’s doing well. Meeting him  __52   my life. Now when I’m in a hurry, or have a bad day, I try extra hard to speak __53   to those around me. I remind myself that it’s just as easy to say something nice as to say something __54  , and I’m awed (敬畏) at how __55   our daily actions are.

36. A. formal          B. polite        C. special          D. usual

37. A. climbed                 B. ran              C. rode             D. moved

38. A. during                B. before          C. until             D. after

39. A. search                 B. walk            C. drive            D. move

40. A. thanks                B. goodbye       C. hello             D. words

41. A. But                    B. Because        C. When           D. Though

42. A. difficult                     B. easy            C. convenient    D. comfortable

43. A. astonished           B. painful       C. embarrassed   D. amazed

44. A. calm                   B. nervous        C. disappointed  D. sorry

45. A. confused        B. worried        C. moved          D. proud

46. A. meant                 B. done            C. caused          D. brought

47. A. working              B. traveling      C. chatting               D. staying

48. A. someone             B. everyone      C. anyone          D. no one

49. A. cold                   B. friendly        C. warm            D. cruel

50. A. use up                B. take up         C. break up       D. pick up

51. A. sell                     B. decorate      C. pack             D. sort

52. A. changed                     B. colored        C. satisfied               D. controlled

53. A. directly               B. loudly          C. kindly           D. softly

54. A. different             B. rude         C. serious       D. interesting

55. A. surprising           B. strange         C. impressive    D. powerful