单选题NADPH+H+的主要作用不包括

单选题真核生物中，1mol葡萄糖经糖有氧氧化可产生ATP摩尔数

单选题醛缩酶的催化产物是

单选题下列哪种物质不是核酸与蛋白质的复合物______ A.核糖体 B.snRNP C.SRP D.核酶 E.端粒酶

单选题比较真核生物与原核生物的DNA复制，二者的相同之处是 A.引物长度较短 B.合成方向是5'→3' C.冈崎片段长度短 D.有多个复制起始点 E.DNA复制的速度较慢(50nt/s)

单选题下面有关snRNA的叙述不正确的是( )。

单选题酶的绝对专一性是指

单选题There are countless parents who will not allow their children to play violent video games, in which players are able to kill, maim, dismember or sexually assault human images in depraved ways. The video game industry rates them, and some stores use that rating to decide whether to sell a particular game to a minor. But California went too far in 2005 when it made it illegal to sell violent video games to minors. Retailers challenged the law, and a federal appeals court rightly ruled that it violates the First Amendment. Last week, the Supreme Court said that it would review that decision. We hope it agrees that the law is unconstitutional. California's law imposes fines of up to $1,000 on retailers that sell violent video games to anyone under 18. To qualify, a game must, as a whole, lack serious literary, artistic, political or scientific value for minors. But video games are a form of free expression. Many have elaborate plots and characters, often drawn from fiction or history. The California law is a content-based restriction, something that is presumed invalid under the First Amendment. The Supreme Court has made it clear that minors have First Amendment rights. California has tried to lower the constitutional standard for upholding the law by comparing it to "variable obscenity," a First Amendment principle that allows banning the sale of some sexually explicit materials to minors that cannot be banned for adults. The United States Court of Appeals for the Ninth Circuit, in San Francisco, like other federal courts, rightly refused to extend that doctrine to violent games. Under traditional First Amendment analysis, content-based speech restrictions can survive only if they are narrowly tailored to promote a compelling government interest. California says its interest is in preventing psychological or neurological damage to young people. The appeals court concluded that the evidence connecting violent video games to this sort of damage is too weak to make restricting the games a compelling government interest. Even if the interest were legitimate, the state could have used less restrictive methods. The video game industry, like the movie business, has a voluntary rating system that provides buyers and sellers with information on the content of specific games, including age-specific ratings, ranging from "early childhood" to "adults only. " The government could do more to promote the use of voluntary ratings by retailers and parents. California lawmakers may have been right when they decided that video games in which players kill and maim are not the most socially beneficial form of expression. The Constitution, however, does not require speech to be ideal for it to be protected.

单选题人体内的不饱和脂肪酸可以自身合成的是

单选题A．磷酸甘油酸激酶B．烯醇化酶C．丙酮酸激酶D．丙酮酸羧化酶

单选题与mRNA中密码子5′-GAC-3′配对识别的tRNA反密码子是

单选题关于DNA二级结构，描述错误的是（　　）。

单选题A．仅螺旋B．β折叠C．B转角D．无规卷曲E．π螺旋

单选题 A.顺式作用元件 B.顺式作用因子 C.反式作用元件 D.反式作用因子 E.全反式作用元件

单选题乙酰CoA是哪个酶的变构激活剂

单选题A．嘌呤碱基B．嘧啶碱基C．嘌呤碱基与嘧啶碱基D．脱氧尿嘧啶核苷酸

单选题 A.转录起始水平 B.复制水平 C.翻译水平 D.翻译后加工水平 E.RNA剪接水平

单选题以DNA为模板，RNA聚合酶作用时，不需要______。 A．NTP B．dNTP C．ATP D．Mg2+/Mn2+

单选题激活的PKC能磷酸化的氨基酸残基是

单选题草酰乙酸不能直接转变生成的物质是