单选题细胞核运输的方向性受Ran蛋白状态直接控制，______存在于细胞核内。

单选题在天然蛋向质的组成中，不含有的氨基酸是( )(2009年)

单选题原核核糖体上结合氨基酰tRNA的氨基酰位的位置是

单选题A．氯霉素B．GTP酶C．转肽酶D．蛋白激酶E．链霉素

单选题It is generally recognized in the world that the second Gulf War in Iraq is a crucial test of high-speed web. For decades, Americans have anxiously (1) each war through a new communication (2) , from the early silent film of World War I to the 24-hour cable news (3) of the first Persian Gulf War. Now, (4) bombs exploding in Baghdad, a sudden increase in wartime (5) for online news has become a central test of the (6) of high-speed Internet connections. It is also a good (7) both to attract users to online media (8) and to persuade them to pay for the material they find there, (9) the value of the Cable News Network persuaded millions to (10) to cable during the last war in Iraq. (11) by a steady rise over the last 18 months in the number of people with high-speed Internet (12) , now at more than 70 million in the United States, the web sites of many of the major news organizations have (13) assembled a novel collage (拼贴) of (14) video, audio reports, photography collections, animated weaponry (15) , interactive maps and other new digital reportage. These Internet services are (16) on the remarkable abundance of sounds and images (17) from video cameras (18) on Baghdad and journalists traveling with troops. And they have found a (19) audience of American office workers (20) their computers during the early combat.

单选题仅仅使DNA单链或者双链断裂而对RNA不起作用的药物是( ) A．博来霉素 B．嘌呤霉素 C．新霉素 D．放线菌素 E．新霉素

单选题膜结构功能的特殊性主要取决于______。

单选题下列DNA中哪一种是单拷贝DNA?( )

单选题当点突变没有带来限制性酶切位点的改变时，不可以采用的诊断技术是( ) A．测序 B．RFLP C．PCR-ASO D．AS-PCR E．核酸分子杂交

单选题人线粒体基因组编码了以下哪类基因?______。 A.tRNA B.DNA聚合酶γ C.RNA聚合酶 D.呼吸链上的所有蛋白质

单选题重组体的筛选方法，不包括

单选题属于反式作用因子的是( ) A．启动子 B．增强子 C．终止子 D．RNA聚合酶 E．转录因子

单选题以下哪一项不会引起插入/缺失(insertion/deletion)突变?

单选题蛋白质分子中的α-螺旋和β-片层都属于

单选题属于肝己糖激酶的同工酶类型是( )(2012年)

单选题某一家族的与G蛋白偶联的腺苷酸环化酶的基因有缺陷，试问下面哪一种激素的功能将会受到影响?______。 A．甲状腺素 B．皮质醇 C．胰岛素 D．肾上腺素 E．ANF

单选题关于玉米的非自主型转座子的转座，以下叙述哪一个是正确的：

单选题A.rRNAB.tRNAC.mRNAD.hnRNA

单选题端粒酶的作用是 A.防止染色体中线性DNA分子末端缩短 B.促进染色体中线性DNA分子末端缩短 C.破坏染色体稳定性 D.促进细胞衰老、凋亡 E.促进细胞中染色体末端融合

单选题以下关于双链DNA变复性过程的描述哪一项是错误的?______。 A.变性过程中A260的光吸收增加 B.GC%含量相同的情况下，碱基排列顺序对Tm值具有明显影响 C.降低DNA溶液中的盐离子浓度，可以提高Tm值 D.双链DNA变性后，沉降速度加快