题干

图表示人类镰刀型细胞贫血症的病因,已知谷氨酸的密码子是GAA、GAG.据图分析正确的是(  )

A:人发生此贫血症的根本原因在于血红蛋白中的谷氨酸被缬氨酸取代

B:②过程是α链作模板,以脱氧核苷酸为原料,由ATP供能,在有关酶的催化下完成的

C:控制血红蛋白的基因中任意一个碱基发生替换都会引起镰刀型细胞贫血症

D:转运缬氨酸的tRNA一端裸露三个碱基是CAU

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答案(点此获取答案解析)

D

同类题1

阅读下面短文,从短文后各题所给四个选项(A、B、C和D)中,选出可以填入空白处的最佳选项,并在答题卡上将该项涂黑

       On our first anniversary, Jack bought a bottle of Casaque, an expensive cologne(古龙香水)for me. "We agreed to save the money for your postgraduate education", I said somewhat half-heartedly as I took it out from a beautifully-wrapped packet. "I am unable not to give something 1 to the world's most beautiful bride, honey!" I held it to my2, and smelled the most pleasant flavor I could ever3. Looking down at my4blue jeans and ugly, ragged tennis shoes, I wondered if I could ever be worthy of it. But I would 5. I used only a little of it every time 6Jack graduated and our life was financially easier. It's a 7the foolish love of a young husband.

       Then one day three-year-old Jim was sitting on the floor8the empty cologne bottle. His lips wet, he was making a(n) 9face. He drank my10cologne! "Jack, come quick," I cried, "can cologne11my baby? Jim drank the rest of it!" "It's mostly just alcohol, honey," Jack12me. Little Jim was fine, and my concern for my child was13. I now felt 14to see the empty cologne bottle.

      A few weeks later, Jack bought another bottle of my beloved cologne. I 15it as much as I had done to the earlier one. 16, it became three-quarters empty. I thought it best to buy another 17. But the shop assistant told me that there wasn't even a maker of that brand any more.

    Now I only use my special cologne on very important occasions, because there will be18to replace it when these last few precious19are gone. But from the bottom of my heart it's not three-quarters empty but still one-quarter full. Perhaps if I'm very careful, I can 20using it for the rest of my life.

同类题4

阅读《冬眠的奥秘》,完成小题

冬眠的奥秘

    ①严寒的冬天,我们总是向往着在被窝里长眠一冬——能像狗熊和青蛙那样冬眠就好了。然而我们大都不知道:那些冬眠的动物们,掌握着我们人类尚不知晓的惊天奥秘。

    ②冬眠是动物应对恶劣环境的一种策略,科学上叫“蛰伏”。有人会问,冬天里睡得多、睡得久,不就是冬眠吗?它们还真不是一回事儿,只是二者的区别不太容易看出来。拿鱼来说,有几类鱼是会冬眠的,包括我们熟悉的鲤鱼、乌鳢,还有海里的鳗鲡。每当冬天来临,它们就把自己调到冬眠档:不吃、不喝、不游动。这看似与正常档的睡觉并无二致,但请注意它们的鳃!鱼类靠鳃呼吸,平时就算身体静止不动,鳃也会轻轻开合扇动。而进入冬眠的鱼,鳃也几乎不动,完全处于麻痹状态。除了呼吸,冬眠动物的体温、心跳等生命指征也都降到极低的水平,新陈代谢速率变得非常缓慢,与休克和死亡标准只差那么一点点——这就是冬眠与睡觉的本质区别。

    ③冬眠的意义在于,尽量减少身体内外的生命活动,将能量消耗降到最低,以挨过环境严酷的时间段。动物冬眠时,能把生命的时钟调得极慢。比如生活在北美洲的普通箱龟,冬眠时心脏5-10分钟才跳1次,实在让人惊叹。更夸张的是,它们几乎完全不呼吸,只靠皮肤吸入少许氧气!

    ④科学家还发现,冬眠不是“习惯养成”的问题,而是遗传基因决定的“天赋”。这种“天赋”还与寿命的长短有联系。一般来讲,哺乳动物的寿命与体型相关,体型小的新陈代谢快,寿命短;体型大的新陈代谢慢,寿命长。比如大象就活80年,兔子七八岁就算高寿。而蝙蝠打破了这个规律——冬眠的菊头蝠和同体型的、不冬眠的老鼠相比,前者可以活到30多岁,后者却只有3、4岁。如果在同一物种中比较,如蝙蝠或者棕熊,依然是冬眠的寿命要长很多。

    ⑤冬眠是当下的热门研究领域。如果人类能像动物们一样冬眠,收获的就绝不仅仅是睡大觉的幸福感,也许还能长生不老。虽然对蝙蝠和棕熊等冬眠动物的研究能确定冬眠基因与长寿有关。但这些动物毕竟与我们人类相差太远。不过,在2004年,有个轰动科学界的发现:居然有一种猴子能冬眠!而人类跟猴子同属灵长类动物,基因相似性很高。如果猴子能冬眠,这意味着我们人类也有可能做到。到那时,我们的寿命说不定可以达到800岁!