| German_Remote_Sensing_Data_Center Information about remote sensing, evaluation and monitoring, with animated satellite data. |
| InfraMation_-_The_Thermographers_Conference Annual conference to be held September 29 through October 2 in Orlando, Florida, for infrared camera users and thermographers involved in predictive maintenance, online process monitoring and non dest |
| Interactive_Visualizer_and_Image_Classifier_for_Satellites General purpose satellite image visualization software which supports MODIS, ASTER, AVHRR, and VIRS data. |
| Land_Use_and_Land_Cover_Group New York Climate and Health Program study to determine the effects of urban growth on public health and air quality in the greater New York using remote sensing data. |
| Landsat_7 United States Geological Survey (USGS): Landsat 7 satellite images. |
| Manuel_Arbelo_-_Department_of_Physics,_University_of_La_Laguna Personal page of a researcher focused on remote sensing and development of satellite algorithm to derive surface temperature (SST and LST). |
| MODIS_(the_MODerate_Resolution_Imaging_Spectroradiometer) Provides extensive and updated information about the Moderate Resolution Imaging Spectroradiometer, flown on two NASA spacecraft (Terra and Aqua) |
| NASA__Multi-angle_Imaging_SpectroRadiometer Page features remote sensing images on the earth's surface. Page includes list of publications, a 3D globe map, and photographs of the imaging instruments. |
| 123_Photogrammetry James Williamson, Ph.D., uses the available photographs or videos along with the Reports and Statements made by Investigators to provide suitable data to have 2D drawings and expand the 2D drawings in |
| Remote_Sensing_Institute_at_Michigan_Tech Promotes research and education in imaging science, atmospheric science, data/signal processing, data visualization and remote sensing instrumentation. |
| Remote_Sensing_Principles Introduction from the Virtual Science Center. |
| Space_Satellite_Sensing MSN community focused on space imagery and online discussion of related topics. |
| ACT_Conferences Organizer of telecommunications technology conferences including wireless web, satellites, and the internet. |
| Aims_for_Future_of_Engineering_Science_(AFES) Sixth International Scientific Forum. Hong Kong, China; 23--30 March 2005. |
| Business_Communications_Company List of meetings covering advanced materials, chemical, energy, food, beverage, packaging, instruments, sensors, safety, security, and construction. |
| CWUAAT Cambridge Workshop on Universal Access and Assistive Technology, incorporating the Cambridge Workshop Series on Rehabilitation Robotics. Discussions focus on rehabilitation robotics to assist the phy |
| Engineering__Conferences_International Interdisciplinary, international engineering conferences. Lists dates, venues and topics. |
| European_Conference_on_Product_and_Process_Modeling_in_the_Building_Industry_(ECPPM) Provides a review of research, development and industrial implementation of product and process technology as it applies to the construction industry. Held every two years. |
| Geotechnical_Seminars Offers location investigation. Seminars held annually in December in the city of Warrington, Cheshire, UK. |
| Integrated_Design_and_Process_Technology_(IDPT) Focuses on knowledge integration through the study of processes leading to the delivery of better quality products and services. Lists past and present meetings. |
| International_Rolling_Technology_Course_(IRTC) Covers major aspects of hot and cold flat rolling. |
| International_Youth_Nuclear_Congress A network of young people interested in nuclear science and technology meeting every two years. Next meeting: Scandinavia in 2006. |
| ISCORMA_-_International_Symposium_on_Stability_Control_of_Rotating_Machinery An annual forum for industry and academia to share knowledge regarding the causes, behavior, and alleviation of instability phenomena in rotating machinery. |
| Material_Science_Technology_Conferences Sponsors international meetings on topics of interest to both researchers and applied industrial applications. |
| Thermo_Sense Presents recent results in the application of thermal imaging to practical problems. XXVII-th meeting: Orlando, Florida, USA; 28 March -- 1 April 2005. |
| Biology_News_Net Daily updated biology news and articles. |
| Bionews__Latest_Biology_News Recent articles and headlines from the biological sciences, biotechnology, and related fields. |
| Etaerio__A_Plant_News_Weblog An aggregation of plant-related news stories, hosted by the UBC Botanical Gardens. |
| Science_News_Presented_by_BIO,_the_Biotechnology_Industry_Organization Developments in genetics, genomics, biotech, and related fields. |
| Topix_net__Biology News about biology, collected from various sources on the web. [RSS] |
| Cytogenetics_Information_Site Study of chromosomes and the diseases caused by numerical and structural chromosome abnormalities. Karyotypes and FISH images of normal and abnormal chromosomes are included. |
| Deoxyribonucleic_Acid Learn about the structure of DNA, how it replicates, protein synthesis and its history. |
| Did_Human_Genome_Map_Vindicate_Darwin? Evolutionists have claimed that the Human Genome Map has proved man evolved from lower animals. Is this fact or fiction? Response from the Institute for Creation Research. |
| eGenome Catalogs a wide range of genomic landmarks, including transcripts, markers, polymorphisms, large-insert clones, and DNA sequences. |
| Genetic_Health Background on genetics, genetic aspects of specific conditions and diseases, counseling and testing, and clinical trials. |
| The_Greatest_Biological_Development_in_Science_History Article about the human genome and its discovery. Includes diagram of the biological Rosetta Stone and a table of human genome statistics. |
| How_Designer_Children_Will_Work Illustrated narrative about the idea of designing babies . Includes mapping the human genome and genetic prescreening |
| Human_Chromosome_Launchpad Information about each human chromosome. Features links to gene maps, sequences, genetic disorders, identified genes, laboratories, and research. |
| Human_Genetics_Programme World Health Organization program which develops genetic approaches to the control of the most common hereditary diseases and those with a genetic predisposition. |
| The_Human_Genome Eighth grade exhibition project providing an introduction with diagrams. Includes information on genetic mutations, gene testing and therapy, and related links. |
The complex arrangements of macromolecules in the virus shell are minute marvels of molecular architecture. Specific requirements of each type of virus have resulted in a fascinating apparent diversity of organization and geometrical design. Nevertheless, there are certain common features and general principles of architecture that apply to all viruses. In 1956, Crick and Watson proposed on theoretical considerations and on the basis of rather flimsy experimental evidence then available, principles of virus structure that have been amply confirmed and universally accepted.They first pointed out that the nucleic acid in small virions was probablyinsufficient to code for more than a few sorts of protein molecules of limitedsize. The only reasonable way to build a protein shell, therefore, was touse the same type of molecule over and over again, hence their theory ofidentical subunits.The second part of their proposal concerned the way in which the subunitsmust be packed in the protein shell or capsid. On general grounds it wasexpected that subunits would be packed so as to provide each with an identicalenvironment. This is possible only if they are packed symmetrically.Crick and Watson pointed out that the only way to provide each subunit withan identical environment was by packing them to fit some form of CUBICSYMMETRY. A body with cubic symmetry possesses a number of axes aboutwhich it may be rotated to give a number of identical appearances. Thesepredictions were soon confirmed and it became evident that the occurrenceof icosahedral features in quite unrelated viruses was not a matter of chanceselection but that icosahedral symmetry is preferred in virus structure. 
An ICOSAHEDRON is composed of 20 facets, each an equilateral triangle, and 12 vertices, and because of the axes of rotational symmetry is said to have 5:3:2 symmetry
Axes of Symmetry There are, in fact, six 5-fold axes of symmetry passing through the vertices, ten 3-fold axes extending through each face and fifteen 2-fold axes passing through the edges of an icosahedron. Icosahedral symmetry requires definite numbers of structure units to complete a shell. In their discussions, Crick and Watson (1956), thinking in terms of asymmetrical protein subunits packed in such a way that each has an identical environment, pointed out that a virus with 5:3:2 symmetry required a multiple of 60 subunits to cover the surface completely. Each unit would be related identically and asymmetrically with its neighbours, and none of the units would coincide with an axis of symmetry.The introduction of NEGATIVE STAINING (Brenner and Horne, 1959) revolutionized the field of electron microscopyof viruses. Within just a few years, much new and exciting information aboutthe architecture of virus particles was acquired. Not only were the overallshapes of particles revealed but also the symmetrical arrangement of theircomponents. This led to a need for a new terminology to describe the viralcomponents.Lwoff, Anderson and Jacob (1959) proposed the terms "capsid" and"capsomers" to represent, respectively, the protein shell and theunits comprising it, and the term"virion" to denote the complete infectivevirus particle (i.e. a capsid enclosing the nucleic acid). This terminologywas generally accepted although it later proved to be inadequate.As soon as the first high resolution micrographs of negatively stainedicosahedral viruses were obtained (Horne et al., 1959 - adenovirus; and Huxleyand Zubay, 1960 - turnip yellow mosaic virus) it seemed that there was astructural paradox. The number of morphological units observed on the surfaceof known icosahedral viruses at that time was never 60 or multiples of 60,and was often more than 60. Furthermore, the capsomers themselves appearedto be symmetrical and were located on symmetry axes, e.g. herpesvirus.Below is a model of the herpes simplex virus capsid
There was direct evidence that capsomers of herpesvirus were hexagonal and pentagonal in section. It is obvious that five-fold capsomers must be located on axes of five-fold symmetry, and six-fold capsomers may be situated on axes of two-fold or three-fold symmetry, or in indifferent sites where they are suited to hexagonal packing. It was therefore clear that the capsomers were not equivalent to the subunits of Crick and Watson (1956). An obvious solution to the problem was provided by supposing that the symmetrical capsomers are built from a number of ASYMMETRICAL SUBUNITS. In this way it is possible to build a variety of complicated bodies in which 5:3:2 symmetry is preserved and in which the number of subunits is a multiple of 60 as predicted by Crick and Watson. The theoretical basis for the structure of isometric viruses was put on afirm foundation by Caspar and Klug (1962) with their concept of identicalelements in quasi-equivalent environments. They defined all possiblepolyhedra in terms of structure units. The icosahedron itself has20 equilateral triangular facets and therefore 20T structure unitswhere T is the TRIANGULATION NUMBER given by the rule: T=Pf
where P can be any number of the series 1,3,7,13,19,21,31 ..(=h
Morphological units can be clustered as 20T trimers, 30T dimersor separated as 60T monomers. The number of morphological units thatwould be produced by a clustering into hexamers and pentamers can be calculatedas follows: There are 10(T-1) hexamers plus 12. (and only 12) pentamers.Caspar and Klug (1962) claimed that most icosahedral viruses fall into2classes:- P=1 and P=3; and that all deltahedra for whichP=>7 are skew, and therefore exist in right and left- handed forms.One "hand" might be selected by the nucleic acid, but there would still bethe chance that mistakes in assembly leading to defective particles mightoccur. The most probable mistake in assembly would be the formation of tubularforms. Tubular structures which have a diameter and surface structure similarto icosahedral virus particles have been observed associated with polyomaand papilloma viruses. In a review of symmetry in virus architecture, Horne and Wildy (1961) showedthat all the viruses then known (with the exception of a few bacteriophages)fell into two main morphological groups:- those with cubic symmetry and the others with HELICAL symmetry. 
"Linear" viral capsids have RNA genomes that are encased in a helix of identical protein subunits. The length of the helical viral nucleocapsid is determined by the length of the nucleic acid. Until 1960, the only known examples of virions with helical symmetry were those of plant viruses, the best studied example being tobacco mosaic virus. 
At that time, the architecture of the myxoviruses was poorly understood.Early electron micrographs of shadow-cast preparations revealed particlesof varying shape and size but little detail could be reported (Bang, 1948).With the advent of negative staining, it became obvious that the myxo-and paramyxo-viruses consisted of an innernucleo-protein component with helical symmetry surrounded by an envelopeof characteristic morphology. This realization of the helical symmetry ofthe myxoviruses laid the foundation for the understanding of the symmetryof other complex groups of viruses such as rabies virus and granulosis virus.In an attempt to clarify the terminology for virus components, Casparet al. (1962) made a number of proposals which were generally accepted.Briefly, the proposals are as follows: The CAPSID denotes the protein shell that encloses the nucleic acid. It is built of structure units. STRUCTURE UNITS are the smallest functional equivalent building units of the capsid. CAPSOMERS are morphological units seen on the surface of particles and represent clusters of structure units. The capsid together with its enclosed nucleic acid is called the NUCLEOCAPSID. The nucleocapsid may be invested in an ENVELOPE which may contain material of host cell as well as viral origin. The VIRION is the complete infective virus particle Go to: Negative Staining EM Images of Animal Viruses © Copyright Linda M Stannard, 1995. This page was written by LindaStannard,on behalf of the Departmentof Medical Microbiology, UCT. Recipient of Key Resource Award 1 border=0> Links2Go Virology Comments are welcomed:- Emailto Stannard@curie.uct.ac.za 