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79 Cards in this Set
- Front
- Back
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what must negative strand RNA carry with them?
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RNA dependent RNA polymerase to form positive strand RNA
(like mRNA) |
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what do retroviruses like HIV carry?
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reverse transcriptase enzyme
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how big are viruses?
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smallest infectious agents
20-300nm |
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how can viruses be used beneficially?
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1. vector for gene therapy (tropism)
2. vaccines (for themselves) 3. bacteriophage to kill bacteria 4. oncolytic viruses (reovirus) |
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why are viruses obligate intracell parasites?
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b/c they can't make energy or macromols (DNA, RNA, proteins) w/o the host cell
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what do viral matrix proteins do?
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mediate interxn b/w capsid and envelope
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what are viral envelopes?
how are they acquired? |
composed of viral (glyco)proteins and host cell derived lipids
acquired by budding during release from cell |
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how would you kill enveloped viruses?
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inactivated by detergents, drying, acid, heat
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how are naked viruses transmitted?
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fomites, small droplets, fecal-oral
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how are enveloped viruses transmitted?
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secretions
LARGE droplets (to fit the envelope in) blood or sexual contact (can't go far w/o contact/secretions) NOT by fecal-oral, inactivated by acid in GI, |
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what does the capsid do?
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w/ or w/o the envelope:
mediates attachment to cells elicits humoral, cellular immune response |
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what happens to the cell during viral release?
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enveloped: budding--won't kill cell (immediately)
naked viruses: lysis (cell death) |
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how are viruses classified?
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1. nucleic acid: type, MW, structure
2. capsid: size, symmetry, +/- envelope 3. replication strategy 4. further divisions based on more detailed criteria (special features) |
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how are viruses grouped?
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1. symptomology
2. tropism 3. mode of transmission (arbovirus) 4. Host (bacteriophage) |
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what are some viral names that reflect characteristics?
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1. reovirus (Respir Enteric Orphan)
2. Toga ("mantle" in gr meaning envelope) 3. picorna (Pico-small, rna-RNA) 4. hepadna (hepa-liver tropic, dna) 5. norwalk (norwalk, OH |
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what are the DNA viruses?
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HHAPPPPy viruses:
Herpes (E) Hepadna (E) Adeno Papilloma Polyoma Parvo Pox (E) (E)=enveloped DNA virus |
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what are the major causes of viral meningitis?
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enteroviruses (80-95%): fecal oral trans
echo and coxsackie also HSV-2 (0.5-3%):DNA, envelope "serious" |
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what are the 2 exceptions to the rule that DNA viruses are ds, icosahedral, and replicate in the nucleus?
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1. parvo: one of the smallest DNA viruses w/ ssDNA ("part of a virus")
2. Pox: biggest DNA virus, complex symmetry, replicates in cytoplasm |
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which 3 DNA viruses are enveloped?
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Herpes, Hepadna, Pox
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which 4 DNA viruses are naked?
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Papilloma, Polyoma, Adeno, Parvo
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what are RNA viruses famous for?
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rate of replication and thus mutation
(RNA pol has no proofreading) |
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what are some RNA viruses?
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toga, corona, retro, picorna, calici, reo, orthomyxo, paramyxo, rhabdo, bunya, arena, filo, flavi, delta (HDV)
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what are the 2 types of capsids?
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icosahedral and helical (RNA only)
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Parvovirus
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1 of 2 exceptions to DNA virus rule:
it has ssDNA "it's as simple as playing a ONE PAR hole in golf) |
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Poxvirus
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1 of 2 exceptions to DNA viruses:
opposite end of spectrum from parvo--extremely complex dsDNA complex structure looks like a box replicates in the CYTOPLASM ("POX IN A BOX") |
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what are some generalities about RNA viruses?
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opposite of DNA viruses:
most ss (half +, half -) enveloped, helical capsid symmetry replicate in the cytoplasm toga, corona, retro, picorna, calici, reo, orthomyxo, paramyxo, rhabdo, bunya, arena, filo |
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what are some odd-ball RNA viruses?
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1. reo--dsRNA, linear, segmented
2. 3 nonenveloped=picorna, calici, reo 3. 5 have icosahedral symm: reo, picorna, toga, flavi, calici (rhabdo helical but bullet shaped) 4. 2 replicate in nuc: retro and orthomyxo |
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which 2 rna viruses replicate in the nucleus?
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orthomyxo (e.g. influenza)
retro |
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viral capsid
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1. contains/protects v genome
2. if naked, mediates attach and has Agenic sites 3. rigid and tough to resist inactivation 4. made of 1 or a few viral encoded protein(s) 5. made of capsomers |
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what is a capsomer?
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structural units of the viral capsid
one or a small number of repeating structural units seen on EM |
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what are the steps of viral replication?
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"RAP US A ViRus!":
Recognition of target/cell Attachment Penetration Uncoating Synth of macromols Assembly Viral Relase |
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What are the phases of viral replication (distinct from the 7 steps of RAP US A ViRus)
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Early phase (before genome rep):RAP, dissassembly/uncoating of viral genome and traffick to approp site
Eclipse period: no viral detection due to dissassembly and start of rep Genome replication Late Phase: synth of macromols, burst |
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what's the burst in viral replication?
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for lytic viruses, can be up to 100.000 virus particles: majority defective (non-infectious) due to muts and assembly errors
occurs at the end of late phase |
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how long does a single viral cycle take?
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depends on virus and the host cell
6-40 hrs |
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what are 2 different types of viral infection?
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productive infection
abortive infection |
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what's a productive infection?
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when viral infection of a cell results in production of infectious progeny
requires a Permissive Cell: cell that supports viral rep |
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whats an abortive infection?
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when viral infection does NOT result in production of infectious progeny virions
may be due to non-permissive cell or defective virus |
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how do viral attachment proteins (VAPs) work?
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via electrostatic interxns:
1. host range (species): tropism may be restricted by VAP specificity 2. naked virus: VAP on capsid 3. enveloped: VAPs=glycoproteins in the env 4. host cell R's: protein, carb, glycopr, or glycolipids |
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how do naked viruses usually enter the cell?
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receptor mediated endocytosis
viropexis(direct penetration of PM) |
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what's viropexis?
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direct penetration of (naked) virus through plasma membrane
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how do enveloped viruses usually enter the cell?
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fusion: fuse w/ PM and release nucleocapsid or genome into cytoplasm
can be pH dependent mediated by viral proteins (e.g. VAP or another prot) |
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how does pH affect the entry of enveloped viruses?
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for some enveloped viruses, fusion occurs at neutral pH on cell surf
others, req acidic pH--receptor mediated endocytosis and fusion occurs in endosomes |
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where does uncoating occur?
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some in the nucleus (rep site for most DNA viruses)
most RNA in cytoplasm *usually nucleoplasmids disassembled to uncoat genome |
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during viral replication, what's the order of synthesis of macromols?
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early mRNA and nonstructural proteins/genes for enzymes and nucleic acid binding proteins
replicate genome late mRNA and structural proteins Post-trans modif of prot |
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what occurs during vDNA replication?
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similar to cellular DNA rep:
initiated at an origin, semi-conserved, require primer small DNA viruses use host DNApol (parvo, papova) lg DNA v encode their own (pox, adeno, herpes) |
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how does replication of hepadna viruses occur?
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by reverse transcription of an RNA intermediate
hepadna--circular dsDNA |
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how do (-) strand RNA viruses rep?
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RNA pol synthesizes (+) strand from (-) strand genome (template)
+ strand then serve as mRNAs for synth of more mRNA and copies of genome |
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what's the only - strand RNA that doesn't have tsc and replication in the cytoplasm?
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influenza virus
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how do tsc and rep work for the dsRNA reo virus?
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1. tsc in core particle in cytoplasm using vDNA pol and (-) strand as template
2. mRNA released from core particle to be trans or encapsulated 3. + RNAs=template for (-) RNA genome rep in new cores reo="REpeatO" virus-dsRNA |
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whats special about retrovirus?
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contain 2 copies of ss (+)RNA genome (diploid), RT, tRNA primers
synth cDNA from +RNA in nucleocapsid (cytoplasm) and deliver to nucleus for integration |
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what kind of genome does HDV have?
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rod-shaped
ssRNA (-) circular extensive intramolecular hybridization helical capsid rep in nucleus by host RNA pol |
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what are infectious nucleic acids?
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some viral genomes infectious in absence of viral proteins
can bypass viral protein-cell R limitations on host range |
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where do viruses assemble?
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site of replication
generally, DNA viruses in nucleus and RNA viruses-cytoplasm icosahedral capsids assembled empty then genome inserted helical capsids form by binding capsomers to genome (and adding RNA pol to - RNA viruses) |
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what does the site of budding depend on for the virus?
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genome type
specific glycoproteins (PM, ER, GA, NucM) |
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what are defective interfering particles?
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since errors common in viral assembly, som defective particles are generated in addition to infectious ones and interfere w their replication
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what kind of virus is picorna
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small ss + RNA
replicates in cytoplasm encodes RNA dependent RNA pol to reproduce itself icosahedral PERCH: Poliovirus Echovirus Rhinovirus Coxsackievirus HAV |
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what kind of virus is rabies?
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- ssRNA, enveloped, carries RDRP in its capsule to make +RNA template
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why is the high mutation rate of influenza significant?
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means we need a new flu vaccine formulation every year
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what's reversion?
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a mutation that results in a change from the mutant genotype to the wt or parental type
*a danger of using live attenuated polio vaccine |
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which kind of nucleic acid virus exists as a "quasi-species"
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RNA viruses, more adaptable than DNA viruses
give rise to spontaneous mutations more frequently |
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what's a lethal mutant phenotype of a virus?
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mutation in essential gene, virus can't replicate
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what's a conditional lethal phenotype mutation of a virus?
what's leakiness? |
mutation that is lethal under one set of conditions (nonpermissive conditions), but not under others ("permissive" conditions)
not all conditional muts are 100% defective under nonperm cond |
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what's a temperature sensitive phenotype mutation of a virus?
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allow replication at low (permissive) but not high (non-permissive) temps
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What's host-range mutatation of a virus?
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mutation that allows replication in one cell type (permissive)
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what's a mutation causing attenuation?
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result in less virulent strain or variant, often developed as vaccine strain
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what's a defective virus?
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lack 1 or more fxnal genes req'd for replication
(require helper activity from another virus in order to rep) |
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what's a defective interfering (DI) virus particle
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spontaneous mutant that interfere w/ replication of helper homologous virus
defective, but retain nl capsid proteins |
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which virus requires an unrelated helper virus?
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HDV
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what's a pseudovirion
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contain only host cell DNA in viral capsid
don't replicate may transduce cellular DNA b/w cells |
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what kinds of interxns occur b/w viruses?
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1. recombination
2. complementation 3. phenotypic mixing |
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what's viral recombination?
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results in progeny that have phenotypic and genotypic differences from either parent
typically by strand brk and recomb or by reassortment |
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what's reassortment?
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viruses w/ segmented genomes can reassort w/ others
ex. influenza, rotovirus |
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what's complementation?
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the interxn of viral gene products in a coinfected cell where 1 or both is defective
1 or both viruses can then replicate (genomes unchanged) using the deficient gene product provided by the other |
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what's phenotypic mixing?
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association of a viral genome w/ a heterologous phenotype:
1. phenotypic maksing or transcapsidation 2. pseudotypes |
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what's phenotypic masking or transcapsidation?
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type of phenotypic mixing where genome of 1 virus incorporated into capsid w/ proteins from another virus (or both)
genetically unstable usually b/w members of same virus family can change tropism of new virion |
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what are pseudotypes?
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type of phenotypic mixing:
nucleocapsid of 1 virus acquires envelope from another virus |
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what's transformation?
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infection can activate or introduce oncogenes
result: uncontrolled growth |
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where are heterophile antibodies found?
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found in pts w/ EBV mononucleosis but nonspecific (variety of viral infections)
None in CMV infection |
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which viruses cause skin rashes?
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rubella, measles, parvo
(mumps and adeno do NOT) |
