单选题下列关于乳酸脱氢酶的叙述哪一项是错误的
单选题转基因方法中最常用、最经典的方法是( ) A．精卵原核显微注射法 B．受体介导法 C．体细胞核移植法 D．脂质体载体法 E．电转移法
单选题对限制性内切酶的作用，下列哪个不正确?( ) A．识别序列长度一般为4～6bp B．只能识别和切割原核生物DNA分子 C．识别序列具有回文结构 D．切割原核生物DNA分子
单选题溶血性黄疸时，不易发生的情况是
A.尿胆素原增加
B.粪胆素原增加
C.尿中出现胆红素
D.粪便的颜色加深
E.血中游离胆红素增加
单选题下列化合物中作为合成IMP、UMP的共同原料的是
单选题生酮氨基酸是
单选题A．IMP B．PRPPC．PRA D APRTE．XMP
单选题三羧酸循环的反应部位在
单选题蛋白质生物合成的部位是
A.细胞核内
B.线粒体膜
C.粗面内质网
D.细胞膜内
E.细胞核膜
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