Introduction to Virology Flashcards
do viruses have a metabolic system of their own?
no
what cells do viruses infect?
prokaryotic cells or eukaryotic cells
what type of genome do viruses have?
DNA or RNA (unique in this)
what is the basic structure of a virus?
nucleic acid genome
protein coat
+/- envelope
what are the three basic types of capsid symmetry?
helical
icosahedral
complex
what virus families have complex symmetry?
bacteriophages
poxviruses
what is the structure of the rabies virus?
helical enveloped
what viruses have an icosahedral naked structure?
picornaviruses
polymaviruses
what viruses have an icosahedral enveloped structure?
herpesviruses
what does it mean for a virus to have an icosahedral structure?
isometric or cubic
what comprises the viral envelope?
lipid bilayer with protein
what may happen if many virions are released simultaneously?
integrity of host cell membrane may be compromised enough to lead to cell death
what are the two basic types of virus-encoded proteins?
structural and non-structural
what do structural proteins typically do?
capsid and genome packaging
what do nonstructural proteins primarily do?
enzymes: genome transcription, replication, and protein processing
if ssRNA serves as a message for translation (the same sense as mRNA), it is referred to as ____________________
positive-sense
if the viral RNA is antisense (or complementary) to that of mRNA- and thus cannot be translated directly- it is said to be ____________________
negative-sense
what are the steps to a virus attacking a host cell?
attachment
penetration
uncoating
multiplication
translation
assembly
release
what is important about viral genetics?
RNA polymerases typically lack error correction ability
viral antigens are important targets for immune response
where do DNA viruses usually replicate?
within the nucleus
where does the replication of most RNA viruses usually take place?
cytoplasm of cells
independent of nuclear machinery
how does the RNA of some animal viruses differ from others?
some have mRNA function and can be directly translated
others have antisense: must first be transcribed into RNAs by a viral-encoded RNA-dependent RNA polymerase
what are the general characteristics of viruses?
smaller than cells
some infect prokaryotic cells, some eukaryotic cells
simple and static structure; no metabolic system of their own
some destroy cells, others persist in latent or persistent state, other cause cellular malignant transformation
how do viruses exit the cell?
enveloped viruses exit via budding
naked virions exit by lysing or exocytosis from the host cell
what viruses only exit via the apical surface?
influenza virus
rabies virus
paramyxovirus
how do viruses impact cell homeostasis?
metabolic derangements
cell lysis or fusion
neoplastic transformation
viral antigens
virus assembly
viral inclusions
reduced host cell DNA, RNA, protein synthesis
what can cell infection result in?
normal
cell death
cytopathology
malignant transformation
what can happen in cytopathology with cell infection?
syncytia
disruption of the cytoskeleton
inclusion bodies
what is pathogenesis?
the origination and development of a disease
acute, chronic, latent, or persistent
susceptibility to infection is a result of a series of factors
what is the pathogenesis of viral infection?
portal of entry
localized vs disseminated infection and tropism
number of cells infected
environmental/host factors
direct and indirect effects
virus-induced immunosuppression
virus-induced immunopathology
evasion of the immune system
what are the host defenses?
physical/chemical barriers
non-specific immune defenses
antibody mediated immunity
cell mediated immunity
what makes viruses a unique class of microorganism?
30-300nm
DNA or RNA genome
obligate intracellular
no cell-free culture
the nucleic acid plus the capsid shell is often called
nucleocapsid
what is the viral envelope derived from?
host cell membranes
no known human or animal viruses have the ________________ structure
naked helical
what does the envelope origin depend upon?
virus and cellular compartment where replication takes place
what do envelope glycoproteins do?
mediate interactions between the virions and cells
what is the genome of poxviruses?
dsDNA whose ends are covalently attached to each other
what viral families have DNA but replicate in the cytoplasm?
poxviruses
iridoviruses
what is a viral family that has RNA but replicates in the nucleus?
orthomyxoviruses
what DNA viruses are associated with oncogenesis?
Marek’s disease virus
bovine, equine, and canine oral papillomaviruses
what RNA viruses are associated with oncogenesis?
retroviridae: avian leukosis virus and feline leukemia virus
the protein coat is formed of structural units called _________________
capsomeres
what viruses are partially double-stranded DNA?
hepadnaviruses
what can a viral genome encode?
a few to greater than 70-100 gene products
what are some examples of evasion of the immune system?
infection of immunologically privileged sites
antigenic variability of virions
inhibition of INF-beta
decrease in MHC class I expression
inhibition in peptide processing and expression of immune system homologous structures
what is an example of immunologic response mediating disease pathogenesis?
Borna disease in horses
what does the host response include?
interferons
cytotoxic T lymphocytes
antibody producing B-lymphocytes
variety of effector molecules
complement
what are some viral propagation methods?
host animals
embryonated eggs
cell/tissue culture
explant culture
primary cell cultures
continuous cell cultures
what are some ways to do indirect enumeration of viruses?
hemaglutination
plaque forming assay
limiting dilution method
what are some virus diagnostics?
virus isolation
Elisa
FA
virus neutralization, HI
PCR, restriction, hybridization, sequencing
RIA
protection tests
collection and submission of specimens
