What are some shapes of viruses

Transmission electron micrograph showing envelope and glycoprotein spikes Coronaviruses ; courtesy of CDC. Transmission electron micrograph of herpes simplex viruses ; courtesy of Dennis Kunkel's Microscopy.

Transmission electron micrograph of the bacteriophage coliphage T4 ; courtesy of Dennis Kunkel's Microscopy. Exercise: Think-Pair-Share Questions We just learned that most viruses are much smaller than bacteria. Compare the sizes of viruses and bacteria. Three or 2 structural proteins make up the papovavirus capsid: in addition, nonstructural proteins are encoded that are functional in virus transcription, DNA replication and cell transformation.

Single-stranded linear DNA, 4—6 kb in size, is found with the members of the Parvovirus family that comprises the parvo-, the erythro- and the dependoviruses. The virion contains 2—4 structural protein species which are differently derived from the same gene product see Ch.

The adeno-associated virus AAV, a dependovirus is incapable of producing progeny virions except in the presence of helper viruses adenovirus or herpesvirus.

It is therefore said to be replication defective. Circular single-stranded DNA of only 1. The isometric capsid measures 17 nm and is composed of 2 protein species only. On the basis of shared properties viruses are grouped at different hierarchical levels of order, family, subfamily, genus and species. More than 30, different virus isolates are known today and grouped in more than 3, species, in genera and 71 families.

Viral morphology provides the basis for grouping viruses into families. A virus family may consist of members that replicate only in vertebrates, only in invertebrates, only in plants, or only in bacteria.

Certain families contain viruses that replicate in more than one of these hosts. This section concerns only the 21 families and genera of medical importance. Besides physical properties, several factors pertaining to the mode of replication play a role in classification: the configuration of the nucleic acid ss or ds, linear or circular , whether the genome consists of one molecule of nucleic acid or is segmented, and whether the strand of ss RNA is sense or antisense.

Also considered in classification is the site of viral capsid assembly and, in enveloped viruses, the site of nucleocapsid envelopment. Table lists the major chemical and morphologic properties of the families of viruses that cause disease in humans. The use of Latinized names ending in -viridae for virus families and ending in -virus for viral genera has gained wide acceptance.

The names of subfamilies end in -virinae. Vernacular names continue to be used to describe the viruses within a genus. In this text, Latinized endings for families and subfamilies usually are not used. Table shows the current classification of medically significant viruses. In the early days of virology, viruses were named according to common pathogenic properties, e.

From the early s until the mids, when many new viruses were being discovered, it was popular to compose virus names by using sigla abbreviations derived from a few or initial letters. Thus the name Picornaviridae is derived from pico small and RNA; the name Reoviridae is derived from respiratory, enteric, and orphan viruses because the agents were found in both respiratory and enteric specimens and were not related to other classified viruses; Papovaviridae is from papilloma, polyoma, and vacuolating agent simian virus 40 [SV40] ; retrovirus is from reverse transcriptase; Hepadnaviridae is from the replication of the virus in hepatocytes and their DNA genomes, as seen in hepatitis B virus.

Hepatitis A virus is classified now in the family Picornaviridae, genus Hepatovirus. Although the current rules for nomenclature do not prohibit the introduction of new sigla, they require that the siglum be meaningful to workers in the field and be recognized by international study groups.

Several viruses of medical importance still remain unclassified. Some are difficult or impossible to propagate in standard laboratory host systems and thus cannot be obtained in sufficient quantity to permit more precise characterization. Hepatitis E virus, the Norwalk virus and similar agents see Ch.

The fatal transmissible dementias in humans and other animals scrapie in sheep and goat; bovine spongiform encephalopathy in cattle, transmissible mink encephalopathy; Kuru, Creutzfeldt-Jakob disease, and Gerstmann-Straussler-Scheinker syndrome in humans see Ch. The agents causing transmissible subacute spongiform encephalopathies have been linked to viroids or virinos i. Some of the transmissible amyloidoses show a familial pattern and can be explained by defined mutations which render a primary soluble glycoprotein insoluble, which in turn leads to the pathognomonic accumulation of amyloid fibers and plaques.

The pathogenesis of the sporadic amyloidoses, however, is still a matter of highly ambitious research. Turn recording back on. National Center for Biotechnology Information , U. Show details Baron S, editor. Search term. General Concepts Structure and Function Viruses are small obligate intracellular parasites, which by definition contain either a RNA or DNA genome surrounded by a protective, virus-coded protein coat.

Classification of Viruses Morphology: Viruses are grouped on the basis of size and shape, chemical composition and structure of the genome, and mode of replication. Nomenclature Aside from physical data, genome structure and mode of replication are criteria applied in the classification and nomenclature of viruses, including the chemical composition and configuration of the nucleic acid, whether the genome is monopartite or multipartite.

Structure and Function Viruses are inert outside the host cell. Classification of Viruses Viruses are classified on the basis of morphology, chemical composition, and mode of replication.

Morphology Helical Symmetry In the replication of viruses with helical symmetry, identical protein subunits protomers self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path. Figure The helical structure of the rigid tobacco mosaic virus rod. Figure Fragments of flexible helical nucleocapsids NC of Sendai virus, a paramyxovirus, are seen either within the protective envelope E or free, after rupture of the envelope. Finally, parasites such as tapeworms can find their way inside the human body and feed on blood and nutrients without killing their host.

Learn more about infectious agents and their impact on human health with this curated resource collection. Even the most basic parts of a cell can enable complex cellular processes, and multifunctional organelles expand these capabilities to make advanced activities possible for higher life-forms.

Organelles are specialized structures that perform various tasks inside cells. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image virus Viruses are microscopic biological agents that invade living hosts and infect their bodies by reproducing within their cell tissue. Photograph by Maryna Olyak. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Some of these drugs stop DNA synthesis, preventing the virus from replicating Although viruses can have devastating health consequences, they also have important technological applications.

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Related Resources. Infectious Agents. Viruses Types. Different Kinds Of Viruses. Common Virus Shapes. Enveloped Icosahedral Virus. Helical Virus Shape. Enveloped Virus Shape. Helical Virus Example. T2 Virus. Virus Shapes And Sizes. Ebola Virus Shape. Lipid Envelope. Types Of Virus Cells.