micro chapter13 2015 - VIRUSES VIROIDS AND PRIONS Chapter...

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VIRUSES, VIROIDS, AND PRIONS Chapter 13
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GENERAL CHARACTERISTICS OF VIRUSES Obligatory intracellular parasites Contain DNA or RNA Contain a protein coat Some are enclosed by an envelope Some viruses have spikes Most viruses infect only specific types of cells in one host Host range is determined by specific host attachment sites and cellular factors
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VIRUS VS. BACTERIA No plasma membrane Do not reproduce by binary fission Don’t possess DNA and RNA simultaneously No ribosomes Don’t make ATP Are not sensitive to antibiotics Contain few or no enzymes of their own
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VIRAL HOST RANGE The spectrum of host cells a virus can infect is called it’s host range Host range is specific Most viruses are only able to infect specific types of cells in specific hosts Viruses that infect only bacteria are called bacteriophages (phages)
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Bacteriophages f2, MS2 Poliovirus Rhinovirus Adenovirus Rabies virus Prion Bacteriophage T4 Tobacco mosaic virus Viroid Vaccinia virus 24 nm 30 nm 30 nm 90 nm 170 × 70 nm 200 × 20 nm 225 nm 250 × 18 nm 300 × 10 nm 300 × 200 × 100 nm Bacteriophage M13 Ebola virus 300 nm E. coli bacterium 3000 × 1000 nm Plasma membrane of red blood cell 10 nm thick Human red blood cell 10,000 nm in diameter Chlamydia bacterium elementary body 800 × 10 nm 970 nm VIRAL SIZE
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VIRION STRUCTURE A completely developed viral particle is called a viron . Nucleic acid DNA or RNA Capsid Capsomeres Envelope Spikes
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VIRAL STRUCTURE: ENVELOPED Roughly spherical Influenza virus Herpes simplex
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ENVELOPED VIRUSES
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VIRAL STRUCTURE: HELICAL Long rods Nucleic acid in a hollow cylindrical capsid Rabies virus Ebola virus
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VIRAL STRUCTURE: POLYHEDRAL Many-sided viruses Many plant and animal viruses of this type Icosahedron Adenovirus Polio virus
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POLYHEDRAL VIRUSES
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COMPLEX VIRUSES bacterial viruses Contain complex structures for transfer of DNA to host cell
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TAXONOMY OF VIRUSES Viruses are grouped into families based on: Nucleic acid type Strategy for replication Morphology The suffix “-ales” is used for orders The suffix “-viradae” is used for families The suffix “-virus” is used as a genus name Common names are used for species.
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