单选题聚合酶链反应可表示为( )。

单选题下列有关SD序列的说法哪个是正确的( ) A．SD序列对真核和原核生物的翻译都是重要的 B．SD序列相对于起始密码子AUG而言，是方向和位置都无关的序列 C．SD序列与反义RNA结合后，对翻译起到抑制作用 D．SD序列对翻译过程的调节作用不大 E．原核生物中的编码基因的翻译共同受到一个上游SD序列的控制

单选题合成冈崎片段不需要______ A.dNTP B.NTP C.引物酶 D.DNA聚合酶 E.DNA连接酶

单选题真核生物体为解决庞大基因组复制问题；的适应性机制是

单选题在进行蓝一白筛选时，pUC载体的lac Z基因位点插入外源DNA，转化细菌后，含有插入了外源DNA的重组质粒的( ) A．细菌不能在含氨苄青霉素的培养板上生长 B．细菌在含有X-gal和诱导剂IPTG的琼脂培养板上形成白色菌斑 C．细菌在含有X-gal和诱导剂IPTG的琼脂培养板上形成蓝色菌斑 D．细菌在含有X-gal和诱导剂IPTG的琼脂培养板上形成透明的无色菌斑 E．无菌落形成

单选题甲氨蝶呤的抗肿瘤作用的生化机制为

单选题真核细胞主动摄取或被动导入外源DNA片段而获得新的表型的过程称为( ) A．转化 B．转染 C．感染 D．侵入 E．诱导

单选题真核生物成熟mRNA 5末端带有帽子结构，一般有三种不同的帽子，其中1号帽子为______。 A．m7GpppNmpNmp B．m7GpppNpNp C．m7GpppNmpNmpNmp D．m7GpppNmpNpNp

单选题A．ras癌基因家族B．myc癌基因家族C．src癌基因家族D．erb癌基因家族E．sis癌基因家族

单选题当溶液的pH与某种氨基酸的pI一致时，该氨基酸在此溶液中的存在形式是( )(2005年)

单选题真核生物RNA聚合酶Ⅱ识别的启动子不含有的元件有：

单选题U5-snRNP在真核mRNA前体拼接中的作用是：

单选题与RNA聚合酶相识别和结合的DNA片段是( ) A．增强子 B．衰减子 C．启动子 D．操纵子 E．沉默子

单选题Few people would defend the Victorian attitude to children, but if you were a parent in those days, at least you knew where you stood: children were to be seen and not heard. Freud and his company did away with all that and parents have been bewildered ever since. The child's happiness is all-important, the psychologists say, but what about the parents' happiness? Parents suffer continually from fear and guilt while their children gaily romp about pulling the place apart. A good "old-fashioned" spanking is out of the question: no modern child-rearing manual would permit such barbarity. The trouble is you are not allowed even to shout. Who knows what deep psychological wounds you might inflict? The poor child may never recover from the dreadful traumatic experience. So it is that parents bend over backwards to avoid giving their children complexes which a hundred years ago hadn't even been heard of. Certainly a child needs love, and a lot of it. But the excessive permissiveness of modern parents is surely doing more harm than good. Psychologists have succeeded in undermining parents' confidence in their own authority. And it hasn't taken children long to get wind of the fact. In addition to the great modern classics on child-care, there are countless articles in magazines and newspapers. With so much unsolicited advice flying about, mum and dad just don't know what to do any more. In the end, they do nothing at all. So, from early childhood, the kids are in charge and parents' lives are regulated according to the needs of their offspring. When the little dears develop into teenagers, they take complete control. Lax authority over the years makes adolescent rebellion against parents all the more violent. If the young people are going to have a party, for instance, parents are asked to leave the house. Their presence merely spoils the fun. What else can the poor parents do but obey? Children are hardy creatures (far hardier than the psychologists would have us believe) and most of them survive the harmful influence of extreme permissiveness which is the normal condition in the modern household. But a great many do not. The spread of juvenile delinquency in our own age is largely due to parental laxity. Mother, believing that little Johnny can look after himself, is not at home when he returns from school, so little Johnny roams the streets. The dividing-line between permissiveness and sheer negligence is very fine indeed. The psychologists have much to answer for. They should keep their mouths shut and let parents get on with the job. And if children are knocked about a little bit in the process, it may not really matter too much. At least this will help them to develop vigorous views of their own and give them something positive to react against. Perhaps there's some truth in the idea that children who have had a surfeit of happiness in .their childhood appear like stodgy puddings and fail .to make a success of life.

单选题尿素中两个氨基来源于

单选题盐析分离蛋白质常用的是______。

单选题真核生物染色体着丝粒周围富含：______。 A.单一DNA序列和常染色质 B.单一DNA序列和异染色质 C.卫星DNA序列和常染色质 D.卫星DNA序列和异染色质

单选题关于酶与底物的关系，正确的是

单选题下列哪种氨基酸体内不能合成，必须靠食物供给

单选题发现断裂基因的学者是( )。