Ch. 6 Microbiology.docx - Viruses General Characteristics...

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VirusesGeneral Characteristics of VirusesoAre they living organisms?oObligate intracellular parasitesoContain either RNA or DNAoUse the metabolic machinery of host cell to synthesize their own nucleic acidsoThey have no or just few enzymes of their own oCan infect: animals, plants, algae, fungi, and bacteriaoThe size of viruses ranges from 20 to 1,400 nmHistoryoLouis Pasteur – rabies caused by a “living thing” Proposed the term “virus” (poison)oIvanowski – discovered that the tabacco plant causing disease is an agents smaller than bacteriaViral ComponentsoNaked VirusesVirus is composed ofNucleic acidProtein coat – capsidoCapsid is composed of protein subunits called capsomeresoEnveloped virusesSome viruses have the capsid covered with an envelope (lipids, proteins, and carbohydrates)
Morphology of VirusesoBases on capsid structure there are three different morphological types:HelicalPolyhedralComplexHelical virusesoNaked helical virusesLong rodsThe capsid is cylindrical with helical structure (Tobacco mosaic virus)oEnveloped helical virusHelical nucleocapsid placed within an envelope (influenza)Polyhedral VirusesoThe capsid is a regular polyhedron with 20 triangular faces (Poliovirus)oNucleic acid packed in the centerThe Viral EnvelopeoRoughly sphericaloSometimes the envelope is covered with spikes (carbohydrates)oFunction of capsid/envelope:Protection Attachment of viruses to the host cellsIntroduction of nucleic acid into host cellComplex VirusesoBacterial viruses – bacteriophages2
Head – polyhedralTail – helicalTail fibersBacterial cells have structures that are external to the cell wall. Which of these does not fall into that category?oRibosomesAt the Core of a VirusoEither DNA or RNA Double/single stranded DNADouble/single stranded RNASingle stranded RNAoPositive-sense (directly translated into proteins)o

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