单选题核酸变性后，可产生的效应是

单选题A．丙二酰CoAB．脂肪酰CoAC．β-羟丁酸D．乙酰乙酰CoA (2010年)

单选题疯牛病发病机制是由于

单选题有的酶存在多种同工酶形式，这些同工酶所催化的反应______。

单选题真核生物基因表达不需要( ) A．衰减子 B．转录因子 C．启动子 D．增强子 E．沉默子

单选题A.含有腺苷酸B.含有维生素B2C.两者均有D.两者均无

单选题A few milliamps of electricity can cause plants to increase synthesis of chemicals. These compounds often also have a pharmacological (related to medicine) or commercial value, so the trick could be used to help increase yields of commercially useful biologicals. Artemisinic acid, from sweet wormwood, for example, is used in malarial medications, and shikonin (紫草素), from the purple gromwell plant, is used against skin infections. Researchers have long known that stressing plants can force them to take defensive action, often ramping up the production of protective chemicals that, for example, make them more resistant to insect attack. It has become common practice to stress such plants into increasing their yields. This is usually clone using physical stress elicitors (诱导子), including bits of the micro-organisms that normally attack the plants, or irritants made from metallic compounds such as copper chloride. These are effective, but they come at a cost. Most elicitors are toxic to plants and can build up in tissues, making it necessary to occasionally "clean" a plant of the chemicals so they keep having the same effect. Recently, research groups at the University of Arizona in Tucson found that the application of an electric current to the hairy roots of the poisonous herb Hyoscyamus muticus stimulated the production of the herb's toxin hyoscyamine (天仙子胺). This unpublished finding inspired Hans Van Etten, also of the University of Arizona, and his colleagues to test sub-lethal levels of electrical currents on other plants, to assess electricity's potential to elevate chemical production. The researchers exposed eight different plant species (ranging from Japanese pagoda tree seedlings to pea plants) to weak electrical currents of 30 milliamps. Seven of the plants increased their production o defensive chemicals. The average boost of chemical production was 20 times, they report in Biotechnology Progress. One plant, a type of alfalfa, increased its chemical yield by 168 times. These values are very similar to those achieved using chemical elicitors, and seem to have no lethal effects-just a negative effect on growth. The treatment can be used over and over again without the build-up of any unwanted material. The useful compounds would be very easy to harvest: they simply pour out into solution if the plants are grown hydroponically. "The fact that we can use electricity instead of toxic materials to elicit chemical production is very exciting because it means we get to look at how these chemicals form without having to constantly add and remove toxins from the system," says Van Etten. "This is a really novel and creative approach that I've never seen before," says plant metabolic engineer Fabricio Medina Bolivar from Arkansas State University in Jonesboro. "The possibilities for using electricity with plants in this way are absolutely tremendous. /

单选题催化PCR的酶______。 A．RNA聚合酶 B．DNA聚合酶 C．TaqDNA聚合酶 D．反转录酶

单选题下列几种DNA分子的碱基组成比例各小相同，哪一种DNA的解链温度最低( )(1999年)

单选题一个氨基酸参人多肽链需要

单选题参与RNA编辑的是：

单选题大肠埃希菌的RNA聚合酶全酶中识别启动子区的是( ) A．σ因子 B．ρ因子 C．γ因子 D．ε因子 E．α因子

单选题下列哪项对电子传递和ADP磷酸化均发生抑制作用

单选题酵母双杂交体系被用来研究______。 A．哺乳动物功能基因的表型分析 B．酵母细胞的功能基因 C．蛋白质的相互作用 D．基因的表达调控

单选题A.胆红素-白蛋白B.胆红素葡萄糖醛酸C.胆红素-Y蛋白D.胆素原

单选题46，XX，t(8；14)(q21.3；q32.3)表示( )。

单选题RNA通常是______ A.线性双链分子 B.环状单链分子 C.线性单链分子 D.环状双链分子 E.以上都不对

单选题能降低血液粘滞度，防止血栓形成的多糖是

单选题遗传病的间接基因诊断是检测与致病基因连锁的( ) A．基因突变 B．基因缺失 C．遗传标志 D．基因重排 E．易感基因

单选题牙体预备时，为减小对牙髓的损害所采取的措施是