单选题下列属于芳香氨基酸的是

单选题人类基因组完全图谱的公布是在( )年2月12日。

单选题原核生物基因转录终止子在终止点前均有( )。

单选题下面关于真核生物翻译的叙述中，哪一个是正确的?( )

单选题在转录过程中，三种真核RNA聚合酶都需要的转录因子是：

单选题制作可摘局部义齿印模，选择的托盘与牙弓内外侧应有多大间隙

单选题研究得最早的核酸分子杂交种类是( ) A．菌落杂交 B．Southern杂交 C．Northern杂交 D．液相杂交 E．原位杂交

单选题利用几根毛发进行基因诊断主要体现了基因诊断的哪项特点( ) A．高特异性 B．应用广泛性 C．高灵敏性 D．早期诊断性 E．唯一性

单选题基因诊断的目标分子不可以是( ) A．DNA B．基因的表达产物 C．RNA D．脂多糖 E．mRNA

单选题The use of chemicals in almost all areas of life has become a commonplace phenomenon. There is growing evidence, however, that chemicals in the environment, including pesticides, may contribute to some illnesses. While studies are still being conducted, preliminary conclusions point to the verdict that such chemicals are indeed negatively impacting those humans to whom they are exposed. Children are especially vulnerable to toxic substances. Pound for pound, they eat, drink and breathe more than adults, all of which exposes them more heavily to those chemicals to which most individuals encounter on a daily basis. Furthermore, their bodies are still in developing stages, exacerbating the negative effects of those chemicals, which negatively impact them. Of 50 types of pesticides commonly used in American schools, a study conducted by the National Coalition Against the Misuse of Pesticides found that many caused negative reactions in laboratory animals. Such negative effects included kidney and liver damage, cancer, and neurological and reproductive problems. These implications of these findings are far-reaching. Given the variety of harmful effects attributed to those pesticides tested, one must pause and consider whether it is wise to continue their use in the nation's schools, where children will be constantly exposed to them. Activists have lobbied for the elimination of such use with a degree of success, and recent findings, if supported by further analysis and confirmation, may help further the cause. A long term solution or alternative, however, remains elusive. In the short run, however, there may be some measures that can be taken to mitigate the harmful effects of dangerous pesticides. The American Medical Association's Council on Scientific Affairs concluded in a 1997 report that given the "particular uncertainty.., regarding the long-term health effects of low-dose pesticide exposures," it is "prudent" for adults and children to limit their exposure and to "consider the use of the least toxic chemical pesticides or non-chemical alternatives. /

单选题基因克隆中能特异切割DNA的酶是( ) 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

单选题蛋白X是一种跨膜蛋白，如果通过分子生物学技术截去它的停止转移序列，那么突变的X在细胞中的最后定位是：

单选题结晶牛胰岛素的人工合成是生命科学上的重要成果，对生命起源问题的哪个阶段提供了有利证据?( )

单选题胆固醇合成的限速酶是

单选题下面不属于蛋白质二级结构中存在的构象是

单选题关于启动子叙述错误的是______ A.原核和真核生物均有 B.调控转录起始 C.与RNA聚合酶结合 D.都不能被转录 E.位于转录起始点附近

单选题胆汁酸生成过程的限速步骤是

单选题遗传密码简并性的特点是 A.防止错位突变翻译出不同的氨基酸 B.引起错位突变 C.密码子与反密码子结合 D.氨基酰-tRNA进入线粒体 E.翻译相同的氨基酸

单选题紫外线照射引起DNA损伤时，细菌DNA修复酶基因表达增强，这种现象被称为( ) A．诱导表达 B．阻遏表达 C．基本的基因表达 D．正反馈 E．负反馈

单选题以下关于顺式作用元件的叙述哪项是错误的( )。