问题 单项选择题 A1型题

下列哪种试剂可使蛋白质的二硫键打开()

A.溴化氢

B.2,4-二硝基氟苯

C.β-巯基乙醇

D.碘乙酸

E.三氯醋酸

答案

参考答案:C

解析:二硫键又称S-S键。是2个-SH基被氧化而形成的-S-S-形式的硫原子间的键。反应:2SH=-S-S-+2H。此键在蛋白质分子的立体结构形成上起着一定的重要作用。为了确定蛋白质的一级结构,首先必须将二硫键打开,使成为线状多肽链。巯基乙醇(还原剂)和尿素(蛋白质变性剂)处理后,可使二硫键断裂。故选C。

单项选择题
阅读理解

第三部分阅读理解(共20小题;每小题2分,满分40分)

阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项,并在答

题卡上将该项涂黑。

A

You can make the difference between this … and this. But how?

This summer, join the International Conservation Scouts on a fun—filled holiday with a difference. Year after year, young people from all around the world get together at one of our sixteen conservation camps. Their shared aim is to help protect the countryside and its wildlife.

Many animals and plants are in danger of disappearing forever. The dormouse, a kind of mouse, for example, needs woodland plants for food and trees to stay in. Its habitat is being destroyed by man and it needs our help to survive.

On a conservation camp holiday, you’ll learn all about nature and how to protect it. Our trained leaders will accompany you and tell you everything you need to know. Because of this you don’t need any experience, just energy and enthusiasm. You will explore the countryside and work to ensure the survival of hundreds of animals and plants and still have plenty of time to enjoy the camp’s excellent sport games and organized nature paths through beautiful scenery.

The International Conservation Scouts is a world—wide organization, so there must be a camp near you. You can spend a splendid holiday at any of the camps for as little as £60, including accommodation and food.

For more information, send for a free conservation camps handbook today:

The International Conservation Scouts

Stanton St. John

Oxfordshire OX 71 TL

THE KEY TO SAVING WILDLIFE IS TO PROTECT NATURAL, HABITATS

YOUR WORK WILL MAKE A DIFFERENCE

56.According to the passage, you can_________at the conservation camps.

A.do experiments on the usual dormouse     B.practise numbers of favorite hobbies

C.enrich your knowledge of wildlife           D.have free accommodation and food

57.Judging from its writing style, this passage seems to be ________

A.a piece of advertisement for the young     B.a serious science report for the young

C.a passage for professional reading            D.a passage for arguing an opinion

58.The International Conservation Scouts is located in_________.

A.16 different countries                             B.some camps near you

C.the United Kingdom                               D.the beautiful countryside