反氢

制造氢比较简单，因为只要将电子和质子混合在一起并让电子围绕着质子旋转即成。而制造反氢就不是这么简单了，因为它是由正电子（带正电荷的电子配对物）和反质子（带负电荷的质子配对物）组成，因此要想制造、贮存和控制它都是非常困难的。上个星期，伊利诺斯巴达维亚国立费米加速器实验室的戴维·克里斯蒂安（DavidC．Christian）和他的同事们宣布了他们的初步成果，他们已发现了7个反氢原子。在2个研究组──日内瓦欧洲粒子物理实验室（CERN）和费米实验室──的早期实验中，研究人员在加速器里制出了接近光速的反质子。这些环流的叵…     

模拟分子运动

模拟分子运动一个复杂的分子，无论是福勒烯、蛋白质，还是ＤＮＡ，都是难以描述的。虽然用棒一球模型能够显示它们的结构，但是，当它伸屈和折迭时是怎样运动的还只能进行猜测。现在，生物化学家与数学家联合用计算机模拟了复杂的分子——有时由数千个原子组成的运动。劳...     

无性繁殖人类胚胎

无性繁殖人类胚胎科学家们已经首次“无性繁殖”出人类胚胎，这种复制研究新领域的闯入引起了伦理学和科学上的争论。１０月１３日，在美国生殖协会召开的年会上，乔治·华盛顿大学的罗伯特·斯蒂尔曼（ＲｏｂｅｒｔＪ·Ｓｔｉｌｌｍａｎ）和杰丽·霍尔（ＪｅｒｒｙＬ·Ｈ...     

Early optical emission from the gamma-ray burst of 4 October 2002

Observations of the long-lived emission--or 'afterglow'--of long-duration gamma-ray bursts place them at cosmological distances, but the origin of these energetic explosions remains a mystery. Observations of optical emission contemporaneous with the burst of gamma-rays should provide insight into the details of the explosion, as well as into the structure of the surrounding environment. One bright optical flash was detected during a burst, but other efforts have produced negative results. Here we report the discovery of the optical counterpart of GRB021004 only 193 seconds after the event. The initial decline is unexpectedly slow and requires varying energy content in the gamma-ray burst blastwave over the course of the first hour. Further analysis of the X-ray and optical afterglow suggests additional energy variations over the first few days.     

MLH3: a DNA mismatch repair gene associated with mammalian microsatellite instability

DNA mismatch repair is important because of its role in maintaining genomic integrity and its association with hereditary non-polyposis colon cancer (HNPCC). To identify new human mismatch repair proteins, we probed nuclear extracts with the conserved carboxy-terminal MLH1 interaction domain. Here we describe the cloning and complete genomic sequence of MLH3, which encodes a new DNA mismatch repair protein that interacts with MLH1. MLH3 is more similar to mismatch repair proteins from yeast, plants, worms and bacteria than to any known mammalian protein, suggesting that its conserved sequence may confer unique functions in mice and humans. Cells in culture stably expressing a dominant-negative MLH3 protein exhibit microsatellite instability. Mlh3 is highly expressed in gastrointestinal epithelium and physically maps to the mouse complex trait locus colon cancer susceptibility I (Ccs1). Although we were unable to identify a mutation in the protein-coding region of Mlh3 in the susceptible mouse strain, colon tumours from congenic Ccs1 mice exhibit microsatellite instability. Functional redundancy among Mlh3, Pms1 and Pms2 may explain why neither Pms1 nor Pms2 mutant mice develop colon cancer, and why PMS1 and PMS2 mutations are only rarely found in HNPCC families.     

缺镁给人类带来新的忧患

据美国政府的一项统计资料;美国人饮食中镁日消费量仅占推荐量的40％。最近,在圣路易斯召开的第22届微量元素与人体健康年会上,研究人员报告,当饮食中镁缺乏还没有产生明显的症状时,实际上人体已有在病态了。经过调查研究后表明:低镁饮食可引起糖尿病、高血压,而孕妇可患有心血管疾病,包括心跳不规则和血压升高等。纽约州斯卡斯代尔的国家     

人类基因疗法获得决定性的进展

最近,联邦顾问委员会正式批准使用基因疗法治疗参试者的研究计划.在这项计划中,研究人员将处理过的白细胞放回皮肤癌患者和免疫系统严重失调的孩子体内.这是人类向“使用基因疗法治疗各种疾病”的目标迈出了里程碑的一步.     

科学家研制出混合血红蛋白

科学家研制出混合血红蛋白人们一直想在水下能多呆会儿，当然在目前情况下是办不到的。但是，鳄鱼却行，这些厚皮的爬行动物在水下可呆一小时以上。鳄鱼在水下呼吸时，二氧化碳在血液中积聚，溶解并形成碳酸氢离子。这些离子和血红蛋白──携氧的红血细胞组分──结合，导...