题干

水母发光蛋白由236个氨基酸构成,其中有三种氨基酸构成发光环,现已将这种蛋白质的基因作为生物转基因的标记。在转基因技术中这种蛋白质作用是(    )

A:促使目的基因导入宿主细胞中

B:促使目的基因在宿主细胞中复制

C:使目的基因容易被检测和选择

D:使目的基因容易成功表达

上一题 下一题 0.0难度 选择题 更新时间:2010-06-13 03:31:58

答案(点此获取答案解析)

C

同类题3

 Many people believe that yellowing and wetness are the greatest enemy of stamps. In fact, stamps are afraid of not only wetness, but also light and dirty things. People protect their stamps in several different ways.

 To protect stamps,we should never touch the stamps with our hands.This avoids moving dirty things onto them. Stamp tweezers (镊子) should be used in all conditions.

 Stamps are printed things. The colour will slowly disappear if the stamps are put in the light for a long time. So we should not put stamps in the light for long. Direct sunlight must be avoided as well.

 Wetness is an important  problem for stamps. Some  collectors  will put stamps  in separate plastic (塑料) bags. However, it is possible that some stamps have taken in some water from the air before they are put into the plastic bags.Stamps yellow easily and rapidly after they take in wet air.To protect the stamps, some people also put the stamps into a special room which has a machine to  keep the air cool and dry. However, not many people can afford that.

 To keep stamps, stamp collectors usually put them under plastic covers. It is a common and simple way. This helps because the plastic cover keeps the stamps off the wet air. It also stops the fingersfrom touching te stamps.

 Some  collectors  prefer  to  store  stamps  inside  a  plastic  box  with  desiccants  (干燥剂).However, we should take care not to let the stamps. touch the desiccants. On top of that, don't  take your stamps out on a wet day.