单选题代谢时能直接生成一碳单位的化合物

单选题别乳糖对乳糖操纵子的作用是( ) A．作为阻遏物结合于操纵基因 B．作为阻遏物结合于阻遏蛋白 C．使阻遏蛋白变构而不能结合DNA D．抑制阻遏基因的转录 E．使RNA聚合酶变构而活化

单选题移码突变最可能由下列哪项因子引起。 ____

单选题胆固醇在体内代谢的主要去路是( )(1992年)

单选题原核生物启动子在-35和-10处有两个中心，-10处的序列对DNA解链有重要作用，此处( )。

单选题TATA框存在于______。 A．聚合酶Ⅱ识别的所有启动子中 B．聚合酶Ⅱ识别的大部分启动子中 C．聚合酶Ⅲ识别的所有启动子中 D．聚合酶Ⅲ识别的大部分启动子中

单选题大肠杆菌中的光复活修复系统能够特异性地修复下列哪种类型的损伤：

单选题有关整合素描述正确的是( ) A．是异源四聚体 B．直接与抑癌基因接触后抑制肿瘤细胞的运动 C．不需要与配体结合 D．是为了去除结构异常的基因 E．具有二价阳离子依赖性的细胞表面糖蛋白

单选题DNA损伤修复机制中，主要修复可影响碱基配对而扭曲双螺旋结构的DNA损伤的修复方式是( ) A．错配修复 B．直接修复 C．核苷酸切除修复 D．碱基切除修复 E．重组修复

单选题Aristotle believed that the heavens were perfect. If they ever were, they are no longer. The skies above Earth are now littered with the debris (残骸) of dead satellites, bits of old rockets and the odd tool dropped by a spacewalking astronaut. Such is the extent of the detritus that the first accidental collision between two satellites has already taken place. It happened in February 2009, when a defunct (废弃的) Russian Cosmos smashed into a functioning American Iridium, destroying both and creating even more space junk. To stop this sort of thing happening again Vaios Lappas of the University of Surrey, in England, has designed a system that will remove satellites from orbit at the end of their useful lives--and as a bonus will scour part of the sky clean as it does so. Dr. Lappas's satellite-removal system employs a solar sail. As light from the sun hits the sail, it imparts a minuscule but continuous acceleration. When a satellite is first launched, the sail is angled in a way that causes this acceleration to keep the satellite in orbit. (Orbits gradually decay as a result of collisions with the small number of air molecules found even at altitudes normally classified as "outer space". ) Solar sails have yet to be used widely to propel spacecraft in this way--several earlier versions came unstuck when the sails failed to unfurl properly-but doing so is not a novel idea in principle The novelty Dr. Lappas envisages is to change the angle of the sail when the satellite has become defunct. Instead of keeping the derelict craft in orbit, it will, over the course of a couple of years, drag it into the atmosphere and thus to a fiery end. Not only that, but the sail will also act like a handkerchief, mopping up microscopic orbital detritus such as flecks of paint from previous launches. A fleck of paint may not sound dangerous, but if travelling at 27 000kph (17 000mph), as it would be in orbit, it could easily penetrate an astronaut's spacesuit. A prototype of Dr. Lappas's design, called CubeSail, will be launched late next year. It weighs just 3kg and, when folded up, measures 30cm (12 inches) by 10era by 10era. Once unfurled, however, the sail will have an area of 25 square metres. If this prototype, which is paid for by EADS, a European aerospace company, proves successful, solar sails might be added to many future satellites. That would enable them to be removed rapidly from orbit when they became useless and would restore to the skies some measure of Aristotelian perfection.

单选题关于snRNA的正确叙述是______。 A．只位于细胞核 B．大多数是高丰度的 C．在进化的过程中是高度保守的 D．基因突变不一定导致其表达产物改变结构 E．基因具有方向性

单选题用酚一氯仿抽提DNA时，通常在氯仿或酚一氯仿中加少许异戊醇，这是因为：______。 A.使蛋白质变性 B.降低表面张力，减少气泡产生 C.增加DNA分子间凝聚力 D.使DNA分子脱水

单选题A．操纵子B．启动子C．增强子D．沉默子E．衰减子

单选题利用重组DNA技术发展新药物的叙述中，错误的是

单选题短期饥饿时，血糖浓度的维持主要依赖的代谢过程是 A.肝糖原分解 B.肌糖原分解 C.糖异生 D.脂肪转化 E.外周组织利用减少

单选题血浆脂蛋白中空腹12～24小时后血浆中不含

单选题以RNA为模板合成双链DNA为(　　　)

单选题用缺口平移法标记DNA探针时，常用( ) A．限制性核酸内切酶 B．DNA聚合酶Ⅰ C．DNA聚合酶Ⅰ大片段 D．DNA连接酶 E．碱性磷酸酶

单选题DNA连接酶的作用是 A.使双螺旋DNA链缺口的两个末端连接 B.使DNA形成超螺旋结构 C.将双螺旋解链 D.合成RNA引物 E.去除引物，填补空缺

单选题关于基因芯片的制备描述错误的是 A.寡核苷酸探针可在芯片上直接合成 B.可将特定基因的PCR产物点在芯片上作为探针 C.芯片设计时应首要考虑探针的特异性 D.探针的长度有一定的限制 E.一个靶基因应只设计一个探针以提高结果的可靠性