单选题DNA和RNA中共有的碱基是（　　）。

单选题限制性内切核酸酶的星号活性是指( )。

单选题GAL4因子能够结合于基因的上游调控序列并激活基因的转录，它的DNA结合结构域属于______。 A．锌指结构 B．亮氨酸拉链结构 C．螺旋-环-螺旋结构 D．螺旋-转角-螺旋结构

单选题下列哪个化合物脱下的2H是通过FADH呼吸链传递产生能量

单选题有关间接基因诊断描述正确的是( ) A．突变基因的异常结构检测 B．针对的是基因的表达产物 C．比直接诊断效果好 D．完全可以替代直接诊断 E．利用连锁遗传标记进行连锁分析

单选题tRNA的反密码子与mRNA的密码子之间的摇摆配对主要由下面哪类碱基配对引起的?( ) A．C·A B．C·U C．G·A D．G·U E．G·G

单选题DNA半保留复制不涉及______ A.冈崎片段 B.引物酶 C.DNA聚合酶 D.氨基酰tRNA合成酶 E.DNA连接酶

单选题维生素B 2 的活性形式是

单选题下列关于DNA分子二级结构的特点的描述，错误的是

单选题校正和置换致病基因是用正常的基因整合入细胞中的( ) A．基因组 B．线粒体 C．蛋白质 D．细胞质 E．RNA

单选题Holliday模型是用于解释以下哪种机制的：

单选题下列哪一个选项最好的描述了在一个已经完全测序的古细菌蛋白中有多少个大肠埃希菌蛋白质的同源物( ) A．PubMed B．ColiBase C．TaxPlot D．MUMiner E．SNP

单选题R-A-G在pH7.0时所带的净电荷为______。

单选题丙酮酸羧化酶的变构激活剂

单选题Leave it to writer Buchwald to bring humor to hospice. Last February, the famed satirist was diagnosed with terminal kidney failure, given three weeks to live, and transferred to a hospice for a quiet goodbye. Then the unexpected happened. His kidneys almost miraculously started working again. The poisons in his blood that were supposed to carry him out in peaceful slumber(死亡) washed out of his system, leaving instead a funny bone stunned and amused by the absurdity of the situation. It's not every day that someone flunks hospice. Seasoned author that he is, Buchwald turned the irony into a book. Only 10 months ago, he was a sad, 80-year-old man with a newly amputated(切除) leg and kidneys on the fritz(发生故障). Despite his family's pleas, he entered a hospice facility, at ease with his Choice to die naturally. Most people don't know much about hospice, the place. It doesn't cure; it cares, relieving physical pain and mental anguish. Most often, cancer or cardiovascular(心血管病) disease carries hospice patients to their end, usually in weeks. But some are put on hold like Buchwald. Buchwald left after five months. In one large study, 6 percent of hospice patients improved enough to be taken off the terminal list and sent home. Buchwald was shocked when the big sleep didn't come. Before Buchwald became the hospice's superstar, he had been the poster boy for depression. But with the help of physicians and medication, he didn't drown. Laugh or cry. Facing natural death, he now offers a message many of his contemporaries need to hear. Older men, particularly those in their 80s, have the highest rate of suicide. Risk factors for them notably include health issues. In fact, suicide often comes soon after they've seen a doctor. On that point, Buchwald notes the medical dearth of smiles and laughter." Look at how often doctors and nurses walk into a patient's room all serious," he says. His prescription? They" need to go to Disney World to be trained." Laughter, of course, is the best medicine, and some studies even show humor is a biological stress reliever. As Buchwald sees it, many humorists use it as therapy to block out periods of hurt or anger. You would not know there were hurts or anger judging by his hospice time. Friends and family smothered Buchwald with love. VIPs beat a path to the hospice door. And they all came bearing food, lots of cheesecake. He thrived. After he planned his funeral, he started up writing again and found he could write wonderfully. Buchwald is now teaching all of us how to live--and to die. Yet he's quick to add," I have had such a good time at the hospice. I am going to miss it./

单选题合成胆固醇的直接原料为

单选题决定肝摄取葡萄糖速率的是(　　　)

单选题下列哪项不符合跨膜主动运输。______

单选题目前使用最广的将外源基因注入动物受精卵的方法是 A.精子载体法 B.显微注射法 C.胚胎干细胞法 D.逆转录病毒载体法 E.脂质体包裹法

单选题抑制dUMP转变成dTMP的是