Biological Sciences
Shape of Viruses
Viruses come in various shapes, including helical, icosahedral, and complex. Helical viruses have a rod-like shape, icosahedral viruses have a symmetrical, polygonal shape, and complex viruses have a combination of shapes. These shapes are determined by the arrangement of the viral capsid proteins and play a crucial role in the virus's ability to infect host cells.
Written by Perlego with AI-assistance
Related key terms
1 of 5
8 Key excerpts on "Shape of Viruses"
eBook - PDF- Edward K. Wagner, Martinez J. Hewlett, David C. Bloom, David Camerini(Authors)
- 2009(Publication Date)
- Wiley-Blackwell(Publisher)
78 BASIC VIROLOGY PART II BASIC PROPERTIES OF VIRUSES AND VIRUS–CELL INTERACTION QUESTIONS FOR CHAPTER 5 1 One structural form used in building virus particles is based on the icosahedron. Describe, either in words or in a diagram, the organization (number of capsomers, etc.) of the simplest virus particle of this form. 2 If a virus has a negative-sense RNA genome, what enzymatic activity (if any) will be found as part of the virion and what will be the first step in expression of the viral genome? 3 List three properties of a virus that might be used as criteria for classification (taxonomy). 4 What is the basis of the Baltimore classification scheme? 5 What are some examples of virus structural proteins? What are some examples of proteins that have enzymatic activity included as part of a virus structure? Viruses grouped by genome and host Rhabdoviridae Paramyxoviridae Bunyaviridae Reoviridae Birnaviridae Varicosavirus Totiviridae Partitiviridae Cystoviridae Hepadnaviridae Caulimoviridae Fuselloviridae Plasmaviridae Phycodnaviridae Rhizidiovirus Poxviridae Baculoviridae Polydnaviridae Iridoviridae Poxviridae Herpesviridae Adenoviridae Polyomaviridae Papillomaviridae Iridoviridae Parvoviridae Circoviridae Geminiviridae Inoviridae Retroviridae Metaviridae Pseudoviridae Coronaviridae Picornaviridae Togaviridae Flaviviridae Tobamovirus Furovirus Pomovirus Capillovirus Benyvirus Leviviridae Narnaviridae Invertebrates Vertebrates Plants Fungi Bacteria Host ss R N A- d s R N A s s R N A + s s R N A - R T s s D N A ds D N A d s D N A - R T Fig. 5.5 The virosphere. Classification of a major portion of the currently known genera of viruses (–viridae) using criteria defined by the International Committee on the Taxonomy of Viruses. Major groupings are based on the nature of the viral genome and the nature of the host.
eBook - PDF- G. E. W. Wolstenholme, Elaine C. P. Millar, G. E. W. Wolstenholme, Elaine C. P. Millar(Authors)
- 2009(Publication Date)
- Wiley(Publisher)
The electron microscope is unique in furnishing morphological information about individual virus particles by direct optical imagery; other biophysical methods must not only deal with the average properties of multitudes of particles but also yield morphological information quite indirectly. General appearance of intact virus particles Only a score or so different viruses have so far been obtained in sufficiently purified form to allow significant electron microscopic observations to be made, but from these observa- tions certain generalizations regarding shape and size map be drawn. The largest of the objects properly called viruses are about 300 mp. in diameter, while the smallest yet observed are about one-fifteenth that size. Although detailed variations in morphology are numerous, it appears likely that all viruses fit into a classification of shapes roughly described as spheres, rods, ellipsoids, and sperm-like forms. The largest viruses are 19 20 ROBLEY C. WILLIAMS non-uniform in size and appear to have a compIex structure involving an outer membrane, a less dense peripheral region, and a dense core. The smaller viruses are distinguished, generally, by an electron microscopic appearance of internal homogeneity and of complete uniformity of size and shape. Most of the smaller viruses seem to inhabit the plant world, but the apparent lack of small animal viruses may be due to our inability to separate in identifiable form such small objects from the welter of other similar particles found abundantly in animal tissues (Williams, 1953a; Bachrach and Schwerdt, 1954). Detailed morphology of some viruses The direct nature of electron microscopic observation carries with it a considerable hazard of misleading information arising from the many artifacts involved in specimen prepara- tion.
eBook - PDFBiotemplating: Complex Structures From Natural Materials
Complex Structures from Natural Materials
- Simon Robert Hall(Author)
- 2009(Publication Date)
- ICP(Publisher)
Viruses are available in large number and monodisperse in terms of morphology and chemical reactivity. In particular, their marked resistivity to many extremes of environment make them amenable to a range of chemical reactions without appreciable loss of morphology. Moreover, the relationship between shape and chemical reactivity (the precise spatial ordering of the same reactive functional group on the protein capsid) means that viruses are able to direct mineralization in a more morphologically defined manner than the equivalent protein when in solution. a b 156 Biotemplating 7.2 Spherical/polyhedral viruses Morphologically, the simplest form of virus which can be used in biotemplating is the spherical or polyhedral type. The production of capsids with well defined interior dimensions and reactivity enable a range of different mineralizations to be carried out, often with particular viruses being particularly suited chemically to particular reactions. An additional advantage for the biotemplating chemist is the fact that the viral capsid presents an inner and outer surface to the environment, meaning that there exist well defined regions of hydrophilicity and hydrophobicity. One of the first studies on the mineralization of a spherical viral capsid involved the cowpea chlorotic mottle virus (CCMV). In this work, CCMV was used as it presented a heterogeneous reaction environment which directed mineralization almost exclusively to the interior of the capsid 1 . The CCMV capsids are 26 nm in diameter, with an inner cavity size of approximately 20 nm in diameter. The protein shell comprises 180 identical protein subunits, which spontaneously self-assemble into capsid form. On assembly, arginine and lysine amino acid residues adopt a conformation towards the interior of the capsid, thereby imbuing the interior with an appreciable positive charge.
eBook - PDF- M.V. Nermut, A.C. Steven(Authors)
- 1987(Publication Date)
- Elsevier Science(Publisher)
PART I General principles of virus architecture This Page Intentionally Left Blank Nermut/Steven (eds) Animal Virus Structure 0 1987 Elsevier Science Publishers B.V. (Biomedical Division) 3 CHAPTER 1 General principles of virus architecture M.V. NERMUT National Institute for Medical Research, London NW7, U. K. 1.1. Introduction A comprehensive definition of viruses should take into account not only their physical and chemical properties, but also their biological and pathological ’ aspects. In this chapter on the structure of viruses we shall refrain from an attempt at a comprehensive definition and will restrict ourselves to the statement that ‘viruses are organized associations of macromolecules’. This physical-chemical concept of viruses provides a basis for understanding the principles of virus ar- chitecture and the mechanisms of virus assembly. However, we should make it clear that there is no unique morphological entity - the virion - but a great variety of architectural solutions to the fundamental principle of viral pathogenesis: the transfer of viral genome from cell to cell. Nevertheless, there are certain common features and general principles in virus architecture and these will be discussed in this chapter. The architecture of a virus is specified primarily by the properties of its consti- tuent macromolecules. They form the ‘basic structural elements’ of the virion, i.e. the morphological entities, that are often observable in the electron microscope (e.g. capsomers, spikes). These usually associate into ‘structural complexes’ form- ed by two or more different types of ‘basic structural elements’, e.g. an envelope is formed by a lipid bilayer and the glycoprotein spikes, a virus core consists of a core shell and a nucleoprotein complex, more complex viruses comprise a nucleocapsid, core shell and envelope or capsid, etc.
eBook - PDF- G. E. W. Wolstenholme, Maeve O'Connor, G. E. W. Wolstenholme, Maeve O'Connor(Authors)
- 2009(Publication Date)
- Wiley(Publisher)
We ourselves have been particularly con- cerned in recent years with the elucidation, to varying degrees of resolution, of the structures of a number of regular viruses. We shall describe here some of the results on spherical viruses, omitting references to the helical rod-shaped viruses, like tobacco mosaic virus, whose general structure is well known. We shall however be deahg with various rod-shaped tubular structures, since, as we shall see below, these are perhaps more properly classed with spherical viruses than with the simple helical viruses. VIRUSES AS SELF-ASSEMBLING SYSTEMS At first sight, it might appear that there are a great variety of ways in which identical subunits can be assembled to b d d a coat or framework for a virus. On the contrary, it has been shown (Caspar and Klug, 1962) that there are only a limited number of types of efficient design possible for a biological container of this sort. The basic assumption in this theory is that the design of the protein coat is determined by the specific bonding properties of 158 DESIGN A N D STRUCTURE OF REGULAR VIRUSES IS9 the identical structure-units from which it is constructed. If the component parts associate spontaneously under appropriate environmental conditions to form the specific structure, the con- struction is a self-assembly process. One of the clearest examples of self-assembly in biology is provided by the tobacco mosaic virus, where the self-assembly process has been reproduced in uitro (Fraenkel-Conrat and Williams, 1955). In a helical virus of this sort the description of the self-assembly process (Watson, 1954) is fairly straightforward, the virus particle growing by the addition of subunits in identical positions. On the other hand, it is by no means obvious how subunits might assemble themselves to pro- duce a doubly-curved structure such as a spherical shell.
eBook - PDF- Frederick A. Murphy, E. Paul J. Gibbs, Marian C. Horzinek, Michael J. Studdert(Authors)
- 1999(Publication Date)
- Academic Press(Publisher)
Some 50 molecules of a small membrane-associated protein, M2 (not shown), form a small number of pores in the lipid bilayer. [A, from J. Mack and R. M. Burnett, in Biological Macromolecules and Assemblies: Virus Structures (F. Jurnak and A. McPherson, eds.), Vol. 1, p. 337. Wiley, New York; 1984; B, from C. F. T. Mattern, Molecular Biology of Animal Viruses (D. P. Nayak, ed.), p. 5. Dekker, New York, 1977.] (also housing attachment ligands but usually not neu- tralizing epitopes) may be seen at higher resolution (Fig- ures 1.11A and 1.11B). Helical Symmetry The nucleocapsid of several RNA viruses self-assembles as a cylindrical structure in which the protein structural units are arranged as a helix, hence the term helical symmetry. It is the shape and repeated occurrence of identical protein-protein interfaces on the structural units that lead to the symmetrical assembly of the helix. In helically symmetrical nucleocapsids the genomic RNA forms a spiral within the nucleocapsid (Figure 1.9). Many of the plant viruses with helical nucleocapsids are rod shaped, flexible or rigid, and nonenveloped. How- ever, in all such animal viruses the helical nucleocapsid is wound into a secondary coil and enclosed within a lipoprotein envelope. Viral Envelopes The virions of the member viruses of many different virus families are enveloped, and in most cases the integrity of 14 1. Viruses as Etiologic Agents I FIGURE 1.10. / I A B C D E F (Upper row) An icosahedron viewed along (A) twofold, (B) threefold, and (C) fivefold axes of symmetry. (Lower row) Differences in the clustering of capsid polypeptides are responsible for the characteristic appearances of particular viruses as seen by negative contrast electron microscopy. (D) When capsid polypeptides are arranged as 60 trimers, structural units themselves are difficult to see; this is the case with foot-and-mouth disease virus.
eBook - PDF- Ellen G. Strauss, James H. Strauss(Authors)
- 2002(Publication Date)
- Academic Press(Publisher)
Electron micrographs of five DNA viruses belonging to different families and of five RNA viruses belonging to different families are shown in Fig. 2.1. The viruses chosen represent viruses that are among the largest known and the smallest known, and are all shown to the same scale for comparison. For each virus, the top micro-graph is of a virus that has been negatively stained, the middle micrograph is of a section of infected cells, and the bottom panel shows a schematic representation of the virus. The structures of these and other viruses are described below. HELICAL SYMMETRY Helical viruses appear rod shaped in the electron micro-scope. The rod can be flexible or stiff. The best studied example of a simple helical virus is tobacco mosaic virus (TMV). The TMV virion is a rigid rod 18 nm in diameter and 300 nm long (Fig. 2.2B). It contains 2130 copies of a single capsid protein of 17.5 kDa. In the right-hand helix, each protein subunit has six nearest neighbors and each subunit occupies a position equivalent to every other capsid protein subunit in the resulting network (Fig. 2.2A), except for those subunits at the very ends of the helix. Each capsid molecule binds three nucleotides of RNA within a groove in the protein. The helix has a pitch of 23 Å and there are 16 1 / 3 subunits per turn of the helix. The length of the TMV virion (300 nm) is determined by the size of the RNA (6.4 kb). Many viruses are constructed with helical symmetry and often contain only one protein or a very few proteins. The popularity of the helix may be due in part to the fact that the length of the particle is not fixed and RNAs or DNAs of different sizes can be readily accommodated. Thus the genome size is not fixed, unlike that of icosahedral viruses. 33 C H A P T E R 2 The Structure of Viruses ICOSAHEDRAL SYMMETRY Virions can be approximately spherical in shape, based on icosahedral symmetry.
eBook - PDF- Nigel J. Dimmock, Andrew J. Easton, Keith N. Leppard(Authors)
- 2015(Publication Date)
- Wiley-Blackwell(Publisher)
H. V. 2008. Encyclopedia of Virology, 3rd edn. Academic Press, San Diego. Richman, D. D., Whitley, R. J., Hayden, F. G. 2009. Clinical Virology, 3rd edn. ASM Press, Washington DC. Zuckerman, A. J., Banatvala, J., Griffiths, P. D., Schoub, B., Mortimer, P. 2009. Principles and Practice of Clinical Virology, 6th edn. John Wiley & Sons, Chichester. Chapter 2 The structure of virus particles All virus genomes are surrounded by proteins which: • protect nucleic acids from nuclease degradation and shearing • contain identification elements that ensure a virus recognizes an appropriate target cell (but plant viruses do not, and enter the cell directly by injection or injury) • contain a genome-release system that ensures that the virus genome is released from a particle only at the appropriate time and location • include enzymes that are essential for the infectivity of many, but not all, viruses • are called structural proteins, as they are part of the virus particle. Chapter 2 Outline 2.1 Virus particles are constructed from subunits 2.2 The structure of filamentous viruses and nucleoproteins 2.3 The structure of isometric virus particles 2.4 Enveloped (membrane-bound) virus particles 2.5 Virus particles with head-tail morphology 2.6 Frequency of occurrence of different virus particle morphologies 2.7 Principles of disassembly: virus particles are metastable All viruses contain protein and nucleic acid with at least 50%, and in some cases up to 90%, of their mass being protein. At first sight it would appear that there are many ways in which proteins could be arranged round the nucleic acid. However, viruses use only a limited number of designs. The limitation on the range of structures is due to restrictions imposed by the considerations of efficiency and stability.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
