题干

某多肽分子式为C21HxOyN4S2(无二硫键),是由下列氨基酸中的某几种作为原料合成的:苯丙氨酸(C9H11NO2)、天冬氨酸(C4H7NO4)、丙氨酸(C3H7NO2)、亮氨酸(C6H13NO2))半胱氨酸(C3H7NO2S)。下列有关该多肽的叙述不正确的是

A:该多肽水解可得到的氨基酸有亮氨酸

B:该多肽是三肽

C:该多肽水解可得到三种氨基酸

D:该多肽的分子式是C21H32O5N4S2

上一题 下一题 0.0难度 选择题 更新时间:2019-11-26 10:04:44

答案(点此获取答案解析)

B

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阅读下面材料,从每题所给的A、B、C、D四个选项中选出最佳选项。

    A new study finds that plants communicate with one another to warn of danger.

    We often consider plants as the furniture of the natural world. They don't move; they don't make sounds, they don't seem to act on anything. But as is often the case, plants talk to each other all the time. And the language is chemical.

Over the years, scientists have reported that different types of plants, from trees to tomatoes, give out chemicals into the air to help neighboring plants. These chemical warnings can spread information about one plant's disease or infestation(虫害), so other plants can protect themselves. But how plants receive and act on many of the information exactly is still mysterious.

    In this week's Science Magazine, researchers in Japan offered some explanations. They have found out one chemical message and traced it all the way from beginning to end.

The scientists looked at tomato plants infested by a common pest(害虫). To start out, they grew plants in two separate plastic spaces connected by a tube(管子). One plant was infested and placed upwind and the other was uninfested and placed downwind. The downwind plants were later exposed(暴露) to the pest. The results showed that plants near sick neighbors before were able to protect themselves better against the pest.

They found one chemical appeared more often in the exposed plants. The chemical is called HexVic. The scientists discovered where HexVic come from, and put it over healthy plants. Those plants were then able to produce HexVic. Researchers made sure that uninfested plants could fight off bugs and diseases. How do they know when to protect themselves? They are warned first by their friendly plant neighbors.

It is not a simple story, and it may be happening in more plant species than tomatoes. It may also be happening with more chemical signals that are still unknown to us. In a word, we know that plants not only communicate, but also look out for one another.