单选题蛋白质一级结构的主要化学键是

单选题目前在转基因小鼠中常用的基因敲除(gene knockout)是根据 ____ 的原理设计的。

单选题合成脂肪酸不需

单选题组成人体蛋白质的20种氨基酸，都是

单选题A．时间特异性B．空间特异性C．组成性表达D．透导表达E．阻遏表达

单选题下列哪种因素不会影响真核细胞中mRNA的稳定性______ A.5'端帽子 B.siRNA C.polyA尾 D.去稳定元件 E.miRNA

单选题苹果酸-天冬氨酸穿梭的生理意义是 A.将草酰乙酸带入线粒体彻底氧化 B.维持线粒体内外有机酸的平衡 C.为三羧酸循环提供足够的草酰乙酸 D.将细胞质中NADH上的H带入线粒体 E.将乙酰CoA转移出线粒体

单选题下列化合物不属于糖异生的原料的是(　　　)

单选题下列物质中，氧化磷酸化的解偶联剂是 A.一氧化碳 B.氰化物 C.鱼藤酮 D.二硝基苯酚 E.硫化氢

单选题tRNA结构中哪个位点是与特定氨基酸结合的位点

单选题哪种血浆脂蛋白运输内源性甘油三酯(　　　)

单选题真核生物5S rRNA基因的启动子在转录结构基因的( )。

单选题下列哪种物质是细胞间信息物质

单选题磺胺类药物抑制细菌生长属于______。

单选题真核生物核DNA复制方式是

单选题真核生物DNA复制速度与原核生物相比： A．相同 B．略快 C．快很多 D．慢很多

单选题We assumed ethics needed the seal of certainty, else it was non-rational. And certainty was to be produced by a deductive model: the correct actions were derivable from classical first principles or a hierarchically ranked pantheon of principles. This model, though, is bankrupt. I suggest we think of ethics as analogous to language usage. There are no univocal rules of grammar and style which uniquely determine the best sentence for a particular situation. Nor is language usage universalizable. Although a sentence or phrase is warranted in one case, it does not mean it is automatically appropriate in like circumstances. Nonetheless, language usage is not subjective. This should not surprise us in the least. All intellectual pursuits are relativistic in just these senses. Political science, psychology, chemistry, and physics are not certain, but they are not subjective either. As I see it, ethical inquiry proceed like this: we are taught moral principles by parents, teachers, and society at large. As we grow older we become exposed to competing views. These may lead us to reevaluate presently held beliefs. Or we may find ourselves inexplicably making certain valuations, possibly because of inherited altruistic tendencies. We may "learn the hard way" that some actions generate unacceptable consequences. Or we may reflect upon our own and others' "theories" or patterns of behavior and decide they are inconsistent. The resulting views are "tested"; we act as we think we should and evaluate the consequences of those actions on ourselves and on others. We thereby correct our mistakes in light of the test of time. Of course people make different moral judgments; of course we cannot resolve these differences by using some algorithm which is itself beyond judgement. We have no vantage point outside human experience where we can judge right and wrong, good and bad. But then we don't have a vantage point from where we can be philosophical relativists either. We are left within the real world, trying to cope with ourselves, with each other, with the world, and with our own fallibility. We do not have all the moral answers; nor do we have an algorithm to discern those answers. Neither do we possess an algorithm for determining correct language usage but that does not make us throw up our hands in despair because we can no longer communicate. If we understand ethics in this way, we can see, I think, the real value of ethical theory. Some people, talk as if ethical theories give us moral prescriptions. They think we should apply ethical principles as we. would a poultice: after diagnosing the ailment, we apply the appropriate dressing. But that is a mistake. No theory provides a set of abstract solutions to apply straightforwardly. Ethical theories are important not because they solve all moral dilemmas but because they help us notice salient features of moral problems and help us understand those problems in context.

单选题新生链延伸过程中tRNA的移动路径为______。

单选题类固醇激素生化信息的传递首先需通过______。

单选题转运肝合成的内源性胆固醇的脂蛋白是