单选题高β-脂蛋白血症病人，血浆脂类含量测定可出现

单选题下面不属于蛋白质二级结构中存在的构象是

单选题胆固醇合成的限速酶是

单选题关于变构调节的叙述哪一项是错误的

单选题糖蛋白糖链合成场所为

单选题Scientists have for the first time used cloning to create human embryos that live long enough in a laboratory dish to have their stem cells harvested. The feat could set the stage for physicians to produce cells and tissues, tailored to a patient's genetic identity that can treat a wide variety of human illnesses. The accomplishment also provides a road map for how to clone a person, an even more divisive undertaking. The new work, performed in South Korea, represents "a major advance in stem cell research. It could help spur a medical revolution as important as antibiotics and vaccines", says Robert Lanza of Advanced Cell Technology (ACT), a company in Worcester, Mass., that's also investigating the promising stem cell strategy called therapeutic cloning. "However, now that the methodology is publicly available", Lanza adds, "I think it is absolutely imperative that we pass laws worldwide to prevent the technology from being abused for reproductive-cloning purposes." While some fertility doctors and a religious cult have claimed success at creating a pregnancy via cloning, they've offered no convincing proof. In contrast, the South Korean research is being reported at the meeting of the American Association for the Advancement of Science in Seattle and will appear in an upcoming Science. "This is reality," says stem cell researcher John Gearhart of Johns Hopkins University. "He4'e is a bona fide, refereed journal saying that a human embryo has been cloned and a cell line derived from it." Although ACT has not yet published a report of a cloned human blastocyst, Lanza says that the South Korean success is "consistent with our own results." Therapeutic cloning appeals to Lanza and physicians because cells made this way could have the same DNA as a patient's cells do and thus avoid rejection after they're transplanted. Seeking a compromise that would permit this strategy to be pursued, many scientists have called for legislation that would ban cloning to produce a baby but allow the creation of cloned embryos to generate stem cells for research or therapies. "The debate has been very polarized," notes bio-ethicist Laurie Zoloth of Northwestern University in Evanston.

单选题下列属于芳香氨基酸的是

单选题The use of chemicals in almost all areas of life has become a commonplace phenomenon. There is growing evidence, however, that chemicals in the environment, including pesticides, may contribute to some illnesses. While studies are still being conducted, preliminary conclusions point to the verdict that such chemicals are indeed negatively impacting those humans to whom they are exposed. Children are especially vulnerable to toxic substances. Pound for pound, they eat, drink and breathe more than adults, all of which exposes them more heavily to those chemicals to which most individuals encounter on a daily basis. Furthermore, their bodies are still in developing stages, exacerbating the negative effects of those chemicals, which negatively impact them. Of 50 types of pesticides commonly used in American schools, a study conducted by the National Coalition Against the Misuse of Pesticides found that many caused negative reactions in laboratory animals. Such negative effects included kidney and liver damage, cancer, and neurological and reproductive problems. These implications of these findings are far-reaching. Given the variety of harmful effects attributed to those pesticides tested, one must pause and consider whether it is wise to continue their use in the nation's schools, where children will be constantly exposed to them. Activists have lobbied for the elimination of such use with a degree of success, and recent findings, if supported by further analysis and confirmation, may help further the cause. A long term solution or alternative, however, remains elusive. In the short run, however, there may be some measures that can be taken to mitigate the harmful effects of dangerous pesticides. The American Medical Association's Council on Scientific Affairs concluded in a 1997 report that given the "particular uncertainty.., regarding the long-term health effects of low-dose pesticide exposures," it is "prudent" for adults and children to limit their exposure and to "consider the use of the least toxic chemical pesticides or non-chemical alternatives. /

单选题对于6－磷酸果糖激酶1，除哪种说法外都是恰当的

单选题下列对蛋白质变性后主要表现的叙述中不正确的是

单选题通过鸟氨酸循环生成尿素时，其分子中的两个氮原子一个直接来自游离的氨，另一个直接来源于( )(1998年)

单选题酶化学修饰调节最常见的方式是

单选题有机磷化合物中毒时抑制胆碱酯酶，此抑制属于

单选题血氨升高最主要的原因是

单选题A．异戊巴比妥B．铁螯合剂C．COD．二硝基苯酚

单选题组成蛋白质的20种氨基酸中除哪一种外，其α碳原子均为不对称碳原子

单选题下列关于ribozyme的叙述，正确的是

单选题胆汁酸生成过程的限速步骤是

单选题下列哪种物质脱下的氢不进入NADH呼吸链

单选题A．尿素B．尿酸C．肌酐D．氨基酸E．胆红素