问题
单项选择题
下列有关氨酰-tRNA合成酶叙述中，哪一项有误（）
A、氨酰-tRNA合成酶促反应中由ATP提供能量，推动合成正向进行
B、每种氨基酸活化均需要专一的氨基酰-tRNA合成酶催化
C、氨酰-tRNA合成酶活性中心对氨基酸及tRNA都具有绝对专一性
D、该类酶促反应终产物中氨基酸的活化形式为R－CH－C－O－ACC－tRNA NH2
答案
参考答案：C
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下列有关氨酰-tRNA合成酶叙述中，哪一项有误（）
A、氨酰-tRNA合成酶促反应中由ATP提供能量，推动合成正向进行
B、每种氨基酸活化均需要专一的氨基酰-tRNA合成酶催化
C、氨酰-tRNA合成酶活性中心对氨基酸及tRNA都具有绝对专一性
D、该类酶促反应终产物中氨基酸的活化形式为R－CH－C－O－ACC－tRNA NH2
参考答案：C
It’s easy to see how the sawfish got its name. These frightful creatures can grow to be more than 6 meters long. Their bodies are flat and winged, like underwater airplanes. And their noses are shaped like chainsaws. Sawfish are food hunters of the sea. When a sawfish is hungry, it waves its sharp-toothed snout（口鼻部）through a group of fish. Then, it lifts its nose and uses its mouth to draw the injured victims. Hardy（适应力强的）population of sawfish thrived in warm waters along coastlines around the world for thousands of years. Over the past 200 years, however, human actions have severely endangered sawfish. Threats include fishing nets that trap the huge animals, often by mistake. Some people collect sawfish’s snouts as prizes: One snout recently sold for nearly $ 1,600 online. In some Asian cultures, the toothy snouts are used in ceremonies to drive evil and disease away. And sawfish are also delicious. A growing demand in Asia for the fish’s fins for a pricey soup has contributed to the fish’s loves. Compared with other fish, sawfish give birth late in life and at slow rates, which makes it hard for them to recover from overfishing. New efforts now aim to restore sawfish population. Beginning next month, an international agreement will provide protection for all seven of the world’s sawfish species. Scientists are hoping that it’s not too late to save the sawfish. Until 1998, “this fish had never been formally studied in the United States,” says Tonya Wiley of the Mote Marine Laboratory in Sarasota, Fla. “We didn’t know such basic things as where they live, what habitat they use, how often they breed, how many young they have — even what age sawfish are when they begin breeding.” Through historical studies and field research, scientists have become aware of how much the fish’s numbers have decreased. Today, there may be 90 percent fewer sawfish than there used to be. Wiley estimates that only 3,000 to 6,000 sawfish remain in US waters. Sawfish
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