单选题维生素A在视黄醛中的活性形式是______。
单选题下列不属于启动子的是
单选题待测的RNA与标记DNA探针的杂交称为( )。
单选题以下哪种DNA结构是起始DNA同源重组所必需的：
单选题某人体细胞中染色体数目为47，称为( )。
单选题下列哪项技术可以进行基因表达水平异常的检测( ) A．SSCP B．Northern印迹杂交 C．Southern印迹杂交 D．ASO E．RFLP
单选题动物饥饿后摄食，其肝纽咆主要糖代谢途径
单选题合成肽链时，与转位有关的酶是
A.肽酰转移酶
B.转位酶
C.水解酶
D.酯酶
E.水合酶
单选题核糖体的E位点指的是______。 A．真核mRNA被加工的位点 B．原核核糖体上tRNA退出的位点 C．核酸内切酶识别核糖体的位点 D．结合mRNA的位点
单选题
蛋白质变性是由于
A、一级结构改变 B、亚基解聚
C、空间构象破坏 D、辅基脱落
E、电性改变
单选题在下列进行DNA部分酶切的条件中，控制哪一项最好?( )
单选题蛋白质生物合成时，下列哪一种物质能识别mRNA上的终止密码
单选题处于活化状态的真核生物基因对DNaseⅠ的敏感度是
A.高度敏感
B.中度敏感
C.低度敏感
D.不敏感
E.不一定
单选题丙酮酸氧化脱羧生成乙酰CoA与许多维生素有关，但除了
单选题生物体内大多数氨基酸脱去氨基生成仅酮酸是通过下面那种作用完成的
单选题A．双螺旋结构B．三叶草结构C．α-螺旋D．帽子结构E．串珠样结构
单选题Modern liberal opinion is sensitive to problems of restriction of freedom and abuse of power. (1) , many hold that a man can be injured only by violating his will, but this view is much too (2) . It fails to (3) the great dangers we shall face in the (4) of biomedical technology that stems from an excess of freedom, from the unrestrained (5) of will. In my view, our greatest problems will be voluntary self-degradation, or willing dehumanization, as is the unintended yet often inescapable consequence of sternly and successfully pursuing our humanization (6) . Certain (7) and perfected medical technologies have already had some dehumanizing consequences. Improved methods of resuscitation have made (8) heroic effort? to "save" the severely ill and injured. Yet these efforts are sometimes only partly successful: They may succeed in (9) individuals, but these individuals may have sever brain damage and be capable of only a less-than-human, vegetating (10) . Such patients have been (11) a death with dignity. Families are forced to bear the burden of a (12) "death watch". (13) the ordinary methods of treating disease and prolonging life have changed the (14) in which men die. Fewer and fewer people die in the familiar surroundings of home or in the (15) of family and friends. This loneliness, (16) , is not confined to the dying patient in the hospital bed. As a group, the elderly are the most alienated members of our society: Not yet (17) the world of the dead, not deemed fit for the world of the living, they are shunted (18) . We have learned how to increase their years, (19) we have not learned how to help them enjoy their days. Yet we continue to bravely and feverishly push back the frontiers (20) death.
单选题果蝇中，一个X连锁隐性基因(sx)是卷刚毛，另一个与之连锁的隐性基因(y)是黄体，有些相斥相组合的双杂合体雌果蝇显示黄体和卷刚毛斑点，这两种斑点形成的原因是______
A.一条染色体的丢失
B.有丝分裂不分离
C.两位点间发生了有丝分裂交换
D.离着丝点最近的位点与着丝点间发生了有丝分裂交换
单选题雌激素可诱导鸡输卵管合成______。
单选题牛磺酸是由下列哪种氨基酸代谢而来( )(1996年)