干酪生产的凝乳酶的开发

用于干酪制造的重组凝乳酶的开发处于激烈竞争中。美国Genencor公司和Chr.汉逊实验公司协作,在重组凝乳酶的商品化工作中取得显著进展。美国Collaborative研究公司(CR)用重组生物制造凝乳酶方法已取得美国专利局许可的专利权。     

真核细胞的基因的组织

一、真核细胞基因的基本结构 1.转录单位: 从已知的数十种基因的顺序,可得出一个具有功能的基因的共同规律,在基因5’端-25至-75区,有CCAAT和TATAAA区(后者又称ATA box或Hogness box),相当于促进子区(Promotor),为体外转录所必需。     

人类胚胎的免疫系统与成人的有着截然不同的起源

UCSF的研究人员首次向我们证实,人类胚胎的免疫系统与成人的免疫系统有着截然不同的起源.相对于成人的免疫系统而言,胚胎免疫系统对待其环境中的外源物质更倾向于适应,而不是去消灭它.这一发现不但使我们能够更加了解新生儿是如何对感染以及疫苗反应的,而且可以用来解释许多难题,比如为何HIV     

没有神经的腿的再生

对于嵘螈肢体的再生,神经系统特别是切割后的残肢裹的神经纤维,一向是被认为有决定性意义的。晚近利用成体或接近变态的幼体的研究证明了:在再生芽基形成之后,切断神经,已经形成的芽基仍然可以继续发育成正常的肢体;但在再生芽基形成之     

审美的眼 怜悯的心

面向公众宣传教育需要考虑受众的兴趣。大熊猫的保护,和它呈现的很可爱的形象关系很大．人们不由得产生一种怜惜的情感．想要去保护它。反观扬子鳄．如果对它难以拍出那样可爱的图片．写不出那样煽情的文章．那就没什么影响。毕竟,人们怜惜可爱的动物．而对丑陋动物的境遇不太关心,这可能是我们人类演化产生和积淀下来的一种情感反应。     

知识的载体 智慧的力量

2009年5月,繁花烂漫的季节,高等教育出版社迎来了55周年华诞,《生命世界》杂志也走过了5年不平凡的历程。我们出版的高质量的教材和学术著作为我国的生命科学人才培养和学科建设发挥了积极的重要作用,受到了广大师生和科研人员的欢迎。《生命世界》在传播生命科学知识、提高大众科学素养方面起到了很好的作用,全国人大常委会副委员长、中国科学院院长路甬祥院士和全国人大常委会副委员长、中国科协主席、     

知识的载体 智慧的力量

2009年5月,繁花烂漫的季节,高等教育出版社迎来了55周年华诞,《生命世界》杂志也走过了5年不平凡的历程。我们出版的高质量的教材和学术著作为我国的生命科学人才培养和学科建设发挥了积极的重要作用,受到了广大师生和科研人员的欢迎。《生命世界》在传播生命科学知识、提高大众科学素养方面起到了很好的作用,全国人大常委会副委员长、中国科学院院长路甬祥院士和全国人大常委会副委员长、中国科协主席、     

诱人的红酒 奇妙的感官

葡萄酒尤其是红葡萄酒是人类古老的发明之一,或者可以说是大自然慷慨馈赠给人类的一份厚礼。往葡葡汁里添加酒精并不会把它变成葡萄酒,葡萄汁的味道永远是单一的,但是葡萄酒却是层次丰富、细腻淳和,具有迷人的诱惑力。在葡萄汁酿成葡萄酒的过程中产生了很多最初没有的香气和味道,人们在品尝、品味和享用葡萄酒的同时,可以像鉴宝一样获得无穷无尽的乐趣。鉴赏一件艺术品,永远要关注其中的每一个细节。一瓶上好的葡萄酒从颜色、香气,到口感回味,每一个细微的变化都可以细细品味。     

性能优良的测定谷氨酸的传感器

现在酶或菌体固定化的生物传感器的研制很盛行,但存在酶不稳定等问题,因此在应用上进展不大。日本味之素公司为降低生产成本,不断开发出优良的检测系统,其中固定化菌体与质谱仪组合而成的谷氨酸传感器已在工厂中应用了2年。     

由吸附的缩氨酸诱导的细胞膜的形变

研究了由一系列相互平行的吸附在细胞膜上的缩氨酸引起的膜的弹性形变,以及膜对缩氨酸的包裹行为,得到膜的平衡方程,用它可以来处理大尺度的形变,弯曲能量、吸附能量和弹性形变的相互竞争导致膜对缩氨酸发生从不吸附到部分吸附乃至完全包裹的结构转变．在膜的形变很小的时候,可以得到系统能量的解析解。     

Geminiviruses: a tale of a plasmid becoming a virus

Background  

Geminiviruses (family Geminiviridae) are small single-stranded (ss) DNA viruses infecting plants. Their virion morphology is unique in the known viral world – two incomplete T = 1 icosahedra are joined together to form twinned particles. Geminiviruses utilize a rolling-circle mode to replicate their genomes. A limited sequence similarity between the three conserved motifs of the rolling-circle replication initiation proteins (RCR Reps) of geminiviruses and plasmids of Gram-positive bacteria allowed Koonin and Ilyina to propose that geminiviruses descend from bacterial replicons.     

Vegetation as a component of a non-nested hierarchy: a conceptual model

Abstract. A general conceptual model of vegetation based on hierarchy theory is presented. The model emphasizes that prediction of vegetation requires consideration of both mechanisms of vegetation change and the constraints within which it occurs. The mechanisms of vegetation change are the responses to and effects upon their surroundings of individual plants. The most general constraints upon vegetation are aspects of the environment not affected by vegetation over successional time, and the pool of species within dispersal range. Examples of such environmental factors include macroclimate and soil parent material. In some cases, vegetation may alter important labile environmental factors such as soil nutrient and water availability. Some vegetation compositions appear to be resistant to changes in the general constraints. Due to both sources, there are multiple possible vegetation compositions given the same general constraints. Disturbance is defined as an abrupt change in the constraints on the vegetation resulting in a change in the vegetation's state or dynamics. Both the recognition of disturbance and the distinction between independent and labile environmental factors depend on the spatial and temporal scale of observation. For example, a particular wildfire at a given stand may be a disturbance, whereas at a larger scale of observation the same event may contribute to the wildfire regime, part of the constraints at that scale. Similarly, levels of soil organic matter may constrain vegetation over short time scales, due to influencing availability of water and nutrients. Over long time scales, the vegetation itself is a primary determinant of soil organic matter content. This model contains elements of both the initial, holistic theory of vegetation and recent, reductionistic approaches. It reiterates the need to considerboth mechanisms and constraints, stressed by contemporary and earlier workers. Hierarchy theory provides new insights concerning sufficient conditions for prediction, possible limits on predictability, and appropriate research strategy.     

Testing a Primary and a Secondary Endpoint in a Group Sequential Design

Summary We consider a clinical trial with a primary and a secondary endpoint where the secondary endpoint is tested only if the primary endpoint is significant. The trial uses a group sequential procedure with two stages. The familywise error rate (FWER) of falsely concluding significance on either endpoint is to be controlled at a nominal level α. The type I error rate for the primary endpoint is controlled by choosing any α‐level stopping boundary, e.g., the standard O'Brien–Fleming or the Pocock boundary. Given any particular α‐level boundary for the primary endpoint, we study the problem of determining the boundary for the secondary endpoint to control the FWER. We study this FWER analytically and numerically and find that it is maximized when the correlation coefficient ρ between the two endpoints equals 1. For the four combinations consisting of O'Brien–Fleming and Pocock boundaries for the primary and secondary endpoints, the critical constants required to control the FWER are computed for different values of ρ. An ad hoc boundary is proposed for the secondary endpoint to address a practical concern that may be at issue in some applications. Numerical studies indicate that the O'Brien–Fleming boundary for the primary endpoint and the Pocock boundary for the secondary endpoint generally gives the best primary as well as secondary power performance. The Pocock boundary may be replaced by the ad hoc boundary for the secondary endpoint with a very little loss of secondary power if the practical concern is at issue. A clinical trial example is given to illustrate the methods.     

Transformation of a psychrotrophic bacterium with a plasmid from a mesophile

The psychrotrophic bacteriumBacillus psychrophilus was transformed with the broadhost-range plasmid pC194. The ability of the transformant to express chloramphenicol (CAM) resistance and the possible effects of such expression on the physiology of the psychrotroph were examined. The transformant exhibited growth rates, filament formation at elevated temperatures, synthesis of cold shock proteins and cold acclimation proteins, similar to the parentalB. psychrophilus.     

Heating of a Local Region of a Branching Streamer as a Starting Point of a Space Leader and a Negative-Leader Step

Plasma Physics Reports - Localized plasma formations called space leaders are observed in streamer coronas of negative leaders of long laboratory sparks. The main leader completes a step when the...