题干

如图表示某一条多肽链,其中有3个甘氨酸(R基为﹣H)且分别位于第8、20、23位.下列叙述正确的是(  )

A:图中多肽只含有一个游离羧基和一个游离氨基

B:用特殊水解酶除去图中的3个甘氨酸,形成的产物比原多肽多5个氧原子

C:用特殊水解酶除去图中的3个甘氨酸,形成的产物中有4条多肽

D:该多肽释放到细胞外需要消耗能量

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D

同类题4

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      老牛头祖祖辈辈生活在农村,农村的青山就是他的骨骼,黑土就是他的肌肉,绿水就是他的血液。可是现在却不得不离开农村了,而且这一离开就是永远,因为土地被征用了,房子被拆迁了,老牛头将不得不进城和儿子生活在一起,过上一种完全陌生的生活。

      老牛头走倒不要紧,哪里的黄土不埋人?问题是家里那些牛怎么办。老牛头一辈子养牛,靠养牛养活了一家人,并送儿子上大学、在城里安家结婚。当听说非搬家不可后老牛头蒙头睡了三天三夜,起床后的第一件事就是卖牛,一头一头油光水滑的牛给人家牵走了,那时刻牛纷纷回过头朝着他哞哞叫,老牛头背过脸去假装看不见,假装那是人家的牛。

      可到只剩下最后一头最高最健壮、短短的黑毛如绸缎一样闪光的大黑时,无论人家出多少钱老牛头都不卖了,因为大黑非同寻常,它救过自个儿的命。前年的一场洪水中,是大黑用两只犄角把老牛头拱上了岸。

      它是老牛头的救命恩人,也是老牛头对农村的最后一丝依恋,你说他哪舍得把它卖掉?可是不卖不行啊,城里那鸽子笼一样的房子哪能容得下一头牛?

      在一次又一次地给大黑喂过最鲜嫩最芳香的蒿草后,老牛头一遍遍抚摸着它,终于开口说:“老伙计,大黑……对不起你了……”

      老牛头把大黑牵上了集市。这样的一头大黑牛太馋人了,大伙纷纷簇拥过来,价钱出的一个比一个高。老牛头只是不言语,到最后老牛头问人家:“牛卖给你后你怎么对它?”

      有人说耕田,老牛头黑了脸;有人说杀了卖肉,被老牛头啐了一脸的唾沫星子……大半天过去了,谁也没能买走大黑。天色渐渐黑下来,他看到还有个人一直没走。

      那人老牛头认识,是邻村的一位老哥们儿,也是个常年养牛的。

      老牛头问他:“我说老哥,你怎么还不回家?”

      那人听了先递根烟给老牛头,点上后叹口气,说:“我养了一辈子牛,从没见过这么好的牛,老哥,你怎么就狠了心卖它呢?”

      老牛头正抽烟,一听这话含在嘴里的烟就抖起来了,好半晌才开得了口:“不卖不行啊,房子全拆迁了,没处养它了。你们村子没拆吧?唉,真好啊!”

      那人点点头,看着大黑的眼里全是赞叹的神色,又像老牛头一样爱怜地一遍遍抚摸牛,说:“我倒是想买它哩,它要是到我家啊,我天天让它喝最干净的泉水 ,吃最嫩最香的草,不会让它受一丁点委屈的,可是,我出不起钱啊……”

      老牛头大叫起来:“老哥,就冲你这番话,大黑——我送给你,一分钱都不要!我只有一个条件,隔三差五的我从城里回来时,你得让牛跟我做会伴!”

      就这么谈成了,真的一分钱不要,老牛头把缰绳交到那邻村的老哥手里后,掉头就走,在夜色里一步也没有回头,任凭大黑一个劲地叫唤,他决不回头!

      一晃,一个多月过去了,老牛头从城里回来了,直奔邻村。那老哥正在小溪边为大黑牛冲洗,一个多月不见,大黑的毛发越发乌亮了。

      乍见老牛头,那老哥一脸的惊诧,说:“我说,个把月不见,你白是白了,可精气神不那么旺哩。”

      老牛头喉头涌动,双眼痴迷地盯着大黑看,说:“老伙计,可想死你了,我夜夜睡不着觉哩……”便伸出手去摸,谁知大黑牛猛地一伸脖子,那双月牙一样的尖角示威似的一扬。

      老牛头大惊:“大黑,是我啊,我是老牛头啊!”

      可是大黑还是冲他发脾气,一点也不让他亲近。

      老牛头终于双手捂脸凄叫起来:“老伙计,连你都不认识我了……”

                                                                                                                             (选自《2013年中国微型小说精选》,略有删改)

同类题5

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    Researchers at Brigham found about one in five teenagers now have some degree of hearing damage. The researchers did not say why hearing loss has risen, but other experts have strong suspicions. One likely culprit, they say, is MP3 players.

    An MP3 player can be dangerous to hearing when its decibel level is turned up too high. High-decibel sounds can damage nerve endings, called hair cells. If a sound is loud enough, the damage can be permanent. A loud sound can shake the membrane (薄膜) on which the hair cells sit- “like an earthquake”. That shake can break or even uproot hair cells. When that happens, the hair cells are finished. Human ears cannot regrow hair cells. Therefore, when listening to an MP3 player, set a volume limit and avoid exposure to loud sounds.

    On the other hand, the loudness of today's music may not be totally under your control. Music companies have been purposely turning up the volume. It's a trend called the fight for loudness.

    Play a CD from the 1990s. Then play a newly released tune. Don't touch the volume control. You'll probably notice that the new CD sounds louder than the old one. Why? Sound engineers who create CDs are using dynamic range compression (压缩), a technology that makes the quiet parts of a song louder and the loud parts quieter. The overall effect of compression is a louder recording.

    Many musicians and sound engineers aren't pleased. They say that compression is driving down the quality of today, s music, making it sound flat and blaring. Gray Hobish, a sound engineer, explains that music should be a combination of loudness and softness. But music companies want to make music louder so it will stand out. That's important in the competition among recording companies.

    What about listeners? Many teenagers listen to music on the go in noisy places and through headphones, all of which reduce sound quality. So young listeners may not notice the poorer quality of modem recordings. “To their ears,” says Hobish, “the music sounds fine. And they are not aware of the hidden threat of the music they are enjoying.”