单选题呼吸链中的递氢体是(　　　)

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 This unpublished finding inspired Hans Van Etten, also of the University of Arizona, and his colleagues to test sub-lethal levels of electrical currents on other plants, to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A．鸟氨酸B．谷氨酸C．组氨酸D．色氨酸E．苏氨酸

单选题参与RNA编辑的是：

单选题胰岛素降血糖是多方面作用的结果，但不包括

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46，XX，t(8；14)(q21.3；q32.3)表示( )。

单选题嘌呤核苷酸补救合成途径中的特异酶是

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

单选题牙体预备时，为减小对牙髓的损害所采取的措施是

单选题下述关于持家基因表达描述最确切的是( )。

单选题关于哺乳类动物DNA复制叙述错误的是 A.RNA引物较小 B.冈崎片段较小 C.DNA聚合酶δ及α参与 D.仅有一个复制起始点 E.片段连接时由ATP供给能量

单选题正常成人血浆中[Ca]×[P]乘积为

单选题男性青年、肝硬变，出现乳房发育、蜘蛛痣，因为

单选题以下哪种物质不属于磷脂______。

单选题生活在高温等极端环境下的细菌，其基因组DNA的突变概率与常温下生存的原核生物相比未见升高，可能的原因是：

单选题拓扑异构酶的作用是

单选题有关遗传密码的叙述正确的是______ A.一个碱基的取代一定造成它所决定的氨基酸的改变 B.终止密码是UAA．UAG和UGA C.连续插入三个碱基会引起密码子移位 D.遗传密码存在于tRNA中 E.真核生物的起始密码编码甲酰化蛋氨酸