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History General properties of viruses. Structure of viruses. General Morphology of virus. Dr. Dalia M. Mohsen Prof. In microbiology One hundred years ago, researchers could not imagine submicroscopic particles. By the I930s,scientists had begun using the word virus, the Latin word for poison, to describe these filterable agents. Dr. Dalia M. Mohsen Prof. In microbiology The nature of viruses, however, remained elusive until 1935, when Wendell Stanley, an American chemist, isolated tobacco mosaic virus, making it possible for the first time to carry out chemical and structural studies on a purified virus. At about the same time, the invention of the electron microscope made it possible to see viruses. Dr. Dalia M. Mohsen Prof. In microbiology Dr. Dalia M. Mohsen Prof. In microbiology The host range of a virus is the: spectrum of host cells the virus can infect. They can infect : Man Animals Insects Plants Bacteria Dr. Dalia M. Mohsen Prof. In microbiology Viruses that infect bacteria are called bacteriophages, or phages. most viruses are able to infect specific types of cells of only one host species. Dr. Dalia M. Mohsen Prof. In microbiology 1. They are very small in size. 2. They contain one kind of nucleic acid (RNA or DNA ) as their genome. 3. They are obligate intracellular parasites i.e. can only replicate inside living cells. 4. They cannot be grown on artificial culture media and are grown in tissue culture, embryonated eggs or living animals. Dr. Dalia M. Mohsen Prof. In microbiology 1. They vary in size from 20-1000 nm. 2. They can pass through bacterial filters. 3. They are only seen by electron microscope. • Each virus particle or virion is composed of : A • Protein coat (Capsid) B • Nucleic acid core Viruses contain either DNA or RNA but not both. The nucleic acid may be linear or circular. Dr. Dalia M. Mohsen Prof. In microbiology • They employ all four possible nucleic acid types: single-stranded DNA, double-stranded DNA, single-stranded RNA, double-stranded RNA. Dr. Dalia M. Mohsen Prof. In microbiology • Functions of the nucleic acid : a) It is the infectious part of the virus b) It carries information the genetic for virus replication . Dr. Dalia M. Mohsen Prof. In microbiology The nucleic acid of a virus is protected by a protein coat called the capsid. It is composed of small protein subunits called capsomers. Dr. Dalia M. Mohsen Prof. In microbiology 1) It protects the viral genome (DNA or RNA )against inactivation by nucleases. 2) It is responsible for the structural symmetry of virions i.e. icosahedral or helical 3) It participates in attachment of virion to susceptible cells. Dr. Dalia M. Mohsen Prof. In microbiology 4) Capsid proteins are important antigen that induce antibodies that neutralize virus infectivity. 5) Variation in capsid proteins is responsible for the different viral serotypes in non- enveloped viruses. Dr. Dalia M. Mohsen Prof. In microbiology • Many viruses are surrounded by lipid or lipoprotein envelope, which may be covered by glycoprotein spike which attach to host cell receptor during the entry of the virus into the cell Dr. Dalia M. Mohsen Prof. In microbiology • virion : • Is a complete, fully developed, infectious viral particle Composed of nucleic acid and surrounded by a protein coat that protects it from the environment. Dr. Dalia M. Mohsen Prof. In microbiology • Viruses may be classified into several different morphological types on the basis of their capsid archi- tecture: 1.Helical Viruses 2.Polyhedral Viruses 3.Enveloped Viruses 4.Complex Viruses Dr. Dalia M. Mohsen Prof. In microbiology • 1.Helical viruses: Helical viruses resemble long rods that may be rigid or flexible. The viral nucleic acid is found within a hollow, cylindrical capsid that has a helical structure Dr. Dalia M. Mohsen Prof. In microbiology • 2. Polyhedral Viruses: The capsid of most polyhedral viruses is in the shape of an icosahedron. A regular polyhedron with 20 triangular faces and 12 corners. The capsomeres of each face form an equilateral triangle. Dr. Dalia M. Mohsen Prof. In microbiology • 3. Enveloped Viruses: As noted earlier, the capsid of some viruses is covered by an envelope. Enveloped viruses are roughly spherical. When helical or polyhedral viruses are enclosed by envelopes, they are called enveloped helical or enveloped polyhedral viruses. Dr. Dalia M. Mohsen Prof. In microbiology • 4. Complex Viruses : • Some viruses, particularly bacterial viruses, have complicated structures and are called complex viruses. One example of a complex virus is a bacteriophage. Some bacteriophages have capsids to which structures are attached. Dr. Dalia M. Mohsen Prof. In microbiology additional • 4. Complex Viruses : • in this figure, notice that the capsid (head) is polyhedral and that the tail sheath is helical. The head contains the nucleic acid. Dr. Dalia M. Mohsen Prof. In microbiology : • Are composed of viral nucleic acid and proteins but cannot replicate without a helper virus, which provides the missing function. These usually have a mutation or a deletion of part of their genetic material. Dr. Dalia M. Mohsen Prof. In microbiology • Contain host cell DNA instead of viral DNA within the capsid. They are formed during infection with certain viruses when the host cell DNA is fragmented and pieces are incorporated within the capsid. Pseudovirions can infect cell, but they don’t replicate. Dr. Dalia M. Mohsen Prof. In microbiology 1) Are infectious particles that are composed solely of protein. 2) They contain no detectable nucleic acid. Dr. Dalia M. Mohsen Prof. In microbiology • is the process of naming viruses and placing them into a taxonomic system. Morphologys Nucleic acid type Host organisms Type of disease they cause • Most clinically important viruses can be classified into groups according to their structural characters into: A •RNA Viruses B •DNA Viruses Dr. Dalia M. Mohsen Prof. In microbiology • DNAviruses are viruses that have DNA but no RNA 1. Hepadnaviruses. 2. Herpesviridae, 3. Papovaviridae 4. Poxviridae 5. Adenoviridae. Dr. Dalia M. Mohsen Prof. In microbiology • Hepadnaviruses cause serum hepatitis. The hepatitis B virus (HBV): • The hepatitis B virus (HBV) is a common form of this virus that enters the body via hypodermic needles, blood transfusion, or sexual relations Dr. Dalia M. Mohsen Prof. In microbiology DNA Non-Enveloped viruses DNA Enveloped viruses Herpes viruses - HSV 1&2 - Varicella - CMV Adenoviruses Hepadna virus (HBV) Pox viruses (Smallpox, Cowpox) Papiloma virus Parvoviruses Polyomaviruses Dr. Dalia M. Mohsen Prof. In microbiology RNA Non-Enveloped viruses RNA Enveloped viruses Picorna viruses Orthomyxoviruses (Influenza virus) Reoviruses Paramyxoviruses (Measles, Mumps, - Enteroviruses (Polio virus &Coxackievirus) - Hepato virus - Rhinoviruses Parainfluenza) Caiciviruses Rhabdoviruses (Rabies virus) Astro viruses Retroviruses (HIV ) Togaviruses (Encephalitis viruses) Flaviviruses (Yellow fever ,Dengue, HCV) Bunyaviruses Filoviruses Arenaviruses Corona viruses Delta virus • Viral the level of order and follows as thus, with the taxon suffixes classification starts at given in italics: Order • Virales • e.g. Herpesvirales Family • Viridae • e.g. Herpesviridae Dr. Dalia M. Mohsen Genus • Virus • e.g. Herpes simplex virus Prof. In microbiology