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27 Cards in this Set
- Front
- Back
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Virus
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consist of nucleic acid, protein, and sometimes lipids
can only replication w/in cells incapable of generating metabolic energy and synthesizing protein most abundant living entities on planet |
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How do viruses replicate in other cells?
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They use the cells ribosomes and cellular metabolic energy
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Virion
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viral particle - nucleic acid and protein coat (capsid)
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Capsid
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protein coat that protects nucleic acids
carries any required enzymes composed of identical subunits (capsomers) |
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Nucleocapsid
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capsid + nucleocapsid
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enveloped viruses
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liquid bilayer membrane and matrix protein b/w nucleocapsid and envelope
bilayer derived from plasma or nuclear membrane of host cell |
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naked viruses
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lack envelope; more resistant to disinfectants; more easily transmitted
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Viral genome
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can be double or single stranded DNA or RNA
Positive sense or negative sense segmented or nonsegmented |
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Virus protein components
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Attachment proteins on virion surface recognize receptors on host cells
Matrix protein: links the nucleocapsid w/lipid envelope Nucleic acid binding proteins Enzymes (like for nucleic acid replication) |
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Icosahedral virus
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icosahedral symmetry allows for lowest energy configuration of particles that can interact isotropically on the surface of a sphere
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helical virus
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simplest way to arrange identical protein subunits that can be stacked in disks to form cylinder
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ICVT
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International Committee on Viral Taxonomy
classifies viruses into orders, families, subfamilies, genera, and species based on genome structure, host cells, shape, disease produced, etc |
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Baltimore Classification
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classifies viruses based on genome structure and mode of replication (ex. double stranded or single, RNA, reverse transcriptase etc)
More useful classification |
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Complex virus
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3rd most common virus shape
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Infection Cycle/Viral Replication Steps
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Receptor recognition and attachment to host cell
Viral entry, uncoating, and release of genome Expression of viral proteins Replication of viral nucleic acid Assemble of progeny virions Release of infections virus from cell |
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Viral Replication: Receptor Recognition and attachment to host cell
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proteins on virion bind to cell surface protein
this determines the type of cell infected/species potential target for vaccines and antiviral agents (vaccines can block interaction of receptors and viral proteins) |
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Viral entry, uncoating, and release of genome
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entire virion enters cell in a vacuole via endocytosis
if enveloped, envelope fuses with plasma membrane via its "spikes" and then enters *bacteria enters cell in same way |
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DNA Virus Replication
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Genome transported to nucleus (nucleocapsid targeted to nucleus)
ssDNA -> dsDNA transpcription of viral DNA by host RNA polymerase transport of viral mRNA to cytoplasm and translation by host cell ribosomes replication of viral DNA in nucleus of host cell packaging of viral DNA into capsids or nucleocapsids |
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Where does packaging of viral DNA into capsids occur?
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Host cell nucleus
EXCEPT: poxviruses, which occur completely in cytoplasm b/c bring their own RNA polymerase |
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RNA virus replication - positive sense
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genome transported to cytoplasm
+ strand acts as mRNA and directs protein synthesis |
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RNA virus replication - negative sense or double stranded RNA
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virion has RNA polymerase that generate + sense by using - sense as a template
virus encodes production of additional RNA dependent RNA polymerase |
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Reverse-Transcribing Viruses - Retroviruses (HIV)
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requires RNA dependent DNA polymerase (reverse trasncriptase)
ssRNA enters cytoplasm w/ reverse transcriptase SSRNA converts to dsDNA via RT dsDNA enters nucleus, integrates into host genome genes trasncribed by HOST RNA polymerase to make viral mRNA and viral genome RNA viral genome, RT, and other proteins are packaged in the cytoplasm |
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Reverse transcribing viruses - Hepatitis B virus
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partially ds-DNA genome enters nucleus, transcribed to RNA by host RNA polymerase. yields mRNA and pregenomic RNA
pre genomic RNA packaged w/RT and converted to partially dsDNA genome prior to release |
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Release of infectious virus from cell
Naked viruses |
virion assembly and packaging completed in cytoplasm and released after virus disrupts plasma membrane and causes death of cell
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Release of infectious virus from cell
Enveloped viruses |
Viral attachment proteins insert into plasma membrane and expose on surface of cell
viral matrix protein attaches to cytoplasmic surface of plasma membrane under attachment proteins nucleocapsid associates with matrix protein and virion buds from the cell *does not involve cell death |
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Prion
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infections protein molecules; no associated nucleic acid
"replicate" by inducing conversion of normal PrPc to PrPsc - which aggregates and is toxic to neurons cause of spongiform encephalopathies ex: Scrapie, chronic wasting diseas, BSE, Kuru, Creutzfield-Jakob |
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Viroid
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Infections RNA molecule, circular, single stranded, smaller than RNA genome
DO NOT encode proteins Base pair w/host mRNA and target it for degradation b/c host enzymes cleave dsRNA |
