问题 问答题

链孢霉的许多营养突变型能在添加精氨酸(Arg)的基本培养基上生长,其中一些突变型能在添加其他物质的基本培养基上生长(+),如下表所示,你认为精氨酸的代谢途径是怎样的

突变类型 生长反应
基本培养基 谷氨半醛 鸟氨酸 瓜氨酸 精氨酸
Arg—8,—9 - + + + +
Arg—4,—5,—6,—7 - - + + +
Arg—2,—3,—12 - - - + +
Arg—1,—10 - - - - +

答案

参考答案:基因的作用决定了酶或其他蛋白质的形成,从而通过生理生化过程,表现出某一个性状。如果某一个基因发生突变,则不能形成相应的酶,或所形成产物的活性发生改变,就出现生化突变型。在同一个代谢过程中,决定前期代谢途径的基因发生改变,则补充其后任一中间产物,均可以完成代谢途径;但是,如果补充该基因所决定的酶之前的中间产物或底物,则无法完成该代谢过程。所以,在上述突变型的培养实验中,可以看出精氨酸的代谢途径如下列过程:
前体→谷氨半醛→鸟氨酸→瓜氨酸→精氨酸

单项选择题
单项选择题

That rapscallion who leaps off the monkey bars, landing smack onto an innocent 3-year-old bystander, and skips off, giggling all the while According to a new paper out of Israel, he may not feel all that bad about the incident. The study, conducted by Dr. In bal Kivenson Bar-On at the University of Haifa, shows that high levels of fearlessness in 3-and 4-year-olds is ply associated with aggression and a lack of sympathy. This news will likely surprise risk-loving America, where parents typically beam with pride when their undaunted child mounts the big slide.

Fearlessness is a far-end point on the spectrum of what psychologists call the "approach and withdrawal dimension"—people’s tendency to approach new stimuli (to gain information and acquire new skills ) and withdraw from unfamiliar stimuli (to avoid danger). Striking the right balance is considered crucial to man’s survival. But what about preschoolers’ There’s a clear downside, Dr. Kivenson Bar-On discovered, after she observed lots of preschool play and machinations. In total, she documented 80 children at preschool, home and in the lab, measuring their propensity for fearlessness and other social and emotional characteristics at the beginning and end of one year. Fearlessness was measured by observing reactions to various fright-inducing situations: separation from parents, the roar of a vacuum cleaner, a jack-in-the-box and the like. Those who displayed greater levels of fearlessness, the study found, had no trouble recognizing facial expressions of anger, surprise, happiness and sadness in other children—but they had a hard time identifying fear.

Over all, they were "emotionally shallow" and showed lower levels of sympathy. They took advantage of friends and lacked regret over inappropriate conduct. "These findings," the paper explains, " suggest that fearlessness in preschool constitutes a clear risk factor for developmental pathways that lead to problems in morality, conscience development, and severe antisocial behaviors. " At the same time, fearless children tended to be highly sociable. "One of the most interesting findings was that we could discriminate between friendliness and sympathy," Dr. Kivenson Bar-On said. "These kids are curious, easygoing and friendly, but they have a hard time recognizing emotional distress in others. "

Jamie Ostrov, a psychology professor at the State University at Buffalo who studies aggression, says that children at the extreme end of the fearless spectrurn "may be charming, but they’re also highly manipulative and deceptive and skilled at getting their way—even at age 3 or 4. " It could be that fearless children need per distress cues to active their autonomic nervous systems, limiting their ability to detect distress cues in others. It seems to be, if I’m not worried about this, you can’t be, either. But should we be

According to the second paragraph, we may know()

A. fearless children are easy to live

B. fearless children’s character downside

C. fearless children are not sensitive to fear

D. fear children are hard to distinguish different kinds of look