Micro Chapter5. - Chapter 5 Viruses General Structure of Viruses \u2022 They differ from other microorganisms in their structure biology and

Micro Chapter5. - Chapter 5 Viruses General Structure...

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Chapter 5 Viruses General Structure of Viruses They differ from other microorganisms in their structure, biology, and reproduction . Viruses are microscopic particles that infect cells Genome is DNA or RNA Cannot reproduce on their own Obligate intracellular parasites - A virus uses the biochemical machinery of its host cell to replicate itself Infect both eukaryotes and prokaryotes - Bacteriophage (phage): Viruses that Infects bacteria Classification Taxonomic classification remains difficult , Currently viruses are classified based on : Morphology Nucleic acid type ( DNA & RNA ( Mode of replication Host organism Disease they cause International Committee on Taxonomy of Viruses (ICTV ( Baltimore Classification ( 7 groups ( Classification Order (-virales ( Family (viridae ( Subfamily (virinae ( Genus (virus (
Species (-virus ( For the determination of order, the type of nucleic acid DNA or RNA, single or double stranded, and the presence or absence of an envelope are used. In addition, other characteristics such as the type of host, the capsid shape, immunological properties, and the type of disease the virus causes are also considered for further detailed virus classification . Baltimore Classification( page106 ( System places the virus into one of seven groups distinguishing the viruses on the basis of the relationship between the viral genome and the messenger RNA Group I Group II Group III Group IV Group V Group VI Group VII ) In modern virus classification the ICTV system is used in conjunction with the Baltimore classification system (. Morphology Size varies from very small, approximately 20 nm (parvovirus), to up to 450 nm (poxvirus ( Most cannot be visualized by light microscopy Exception to the size is the Mimi virus found in 2003 - Has a diameter of 750 nm and was found in free-living amoebas - Largest known viral genome (~1000 genes on a double-stranded circular DNA ( - Ebola - 970 n m Morphology Viruses consist of genetic material carried in the viral coat or capsid The capsid consists of proteins coded by viral genes
The capsid is a complex structure and serves as the basis for morphological distinction Subunits referred to as protomeres assemble to form capsomeres , which in turn spontaneously aggregate to form the capsid . General Structure of Animal Virus Morphology Proteins associated with nucleic acids are called nucleoproteins The association of viral capsid proteins with viral nucleic acid is referred to as a nucleocapsid Spikes : Long projections from the nucleocapsid Virion : Fully assembled virus Classification :Based on shape and arrangement of capsomeres of an envelope- classified into 4 morphological types : Helical Viruses Icosahedral Viruses Enveloped Viruses Complex Viruses . Classification by Morphology 1 Helical viruses Capsids with rod-shaped capsomeres Genetic material can be single-stranded RNA (ssRNA) or single-stranded DNA (ssDNA ( Can be naked (e.g., tobacco mosaic virus) or enveloped (e.g., influenza virus (
2 Icosahedral viruses Three-dimensiona

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