Micro Chapter 13(1).ppt - Chapter 13 Viruses Viroids Prions General Characteristics of Viruses \u2022 Obligatory intracellular parasites require living

Micro Chapter 13(1).ppt - Chapter 13 Viruses Viroids Prions...

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Chapter 13: Viruses, Viroids, & Prions
General Characteristics of Viruses Obligatory intracellular parasites: require living within a host to multiply Contain DNA or RNA Contain a protein coat Some are enclosed by an envelope Some viruses have spikes No ribosomes No ATP-generating mechanism
Host Range Spectrum of host cells a virus can infect Most viruses infect only specific types of cells in one host Determined by specific host attachment sites & cellular factors Bacteriophages: viruses that infect bacteria
Virus Sizes Range from 20 nm to 1000 nm in length
Virion Structure Virion: complete, fully developed viral particle Nucleic acid DNA or RNA; single or double strained Double stranded DNA Single stranded DNA Double stranded RNA Single stranded RNA Plus strand RNA Minus strand RNA Capsid: protein coat of virus that surrounds nucleic acid Capsomeres: protein subunit of viral capsid Capsid protects nucleic acid of nonenveloped virus
Virion Structure Envelope: outer covering surrounding capsid of some viruses Spikes: carbohydrate- protein complex that projects from surface of certain viruses
General Morphology Helical virus: resemble long rods; may be rigid or flexible; nucleic acid found in hollow cylindrical capsid Ex. Rabies & Ebola Polyhedral viruses: many sided; capsid is in shape of icosahedron (20 triangular faced with 12 corners) Ex. Adenovirus & poliovirus
General Morphology Enveloped virus: roughly spherical; called enveloped helical or enveloped polyhelical Ex. Influenza virus & herpes simplex virus Complex virus: virus with complicated structure Ex. bacteriophage
Taxonomy of Viruses Group viruses into families based on nucleic acid type, strategy for replication & morphology Order names end in –ales ( Herpesvirales) Family names end in –viridae ( Herpesviridae ) Genus names end in –virus ( Herpesvirus ) Viral species: group of viruses sharing same genetic information & ecological niche (host) Common names are used for species (Human herpes virus HHV) Subspecies are designated by a number (Human herpes virus HHV-1)
Growing Viruses Viruses must be grown in living cells Bacteriophages are grown in bacteria Bacteriophages form plaques (clearings) when grown on a lawn of bacteria Each plaque corresponds to a single virus; can be expressed as plaque- forming units (PFU) Animal viruses may be grown in living animals or in embryonated eggs Used to make some vaccines
Growing Viruses Animal & plant viruses may be grown in cell culture Primary cell line: human tissue cells that grow for only few generations in vitro Continuous cell lines (cancer cells) may be maintained indefinitely Figure 13.8

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