Classification & Replication of Viruses (2) Flashcards
Viruses can replicate only in _____ cells of animals, plants, and bacteria
living cells
Viruses are [intermediate/obligate] parasites that are metabolically inert when they are outside of their hosts
obligate
What do viruses rely on?
on the metabolic processes of their hosts to reproduce themselves
the viral diseases we see are due to host’s response to it
What is a prion?
a misfolded protein
not a virus, or any other recognized infectious agent
What do all prions affect?
the structure of the brain or other neural tissue
progressive
have no known effective treatment
always fatal
What are prions resistant to?
resistant to denaturation by chemical and physical agent
What is a proteopathy?
disease of structurally abnormal proteins
a prion is an example of this
What is the structure of a virus?
capsid
envelope
nucleic acid core (DNA or RNA)
Viral proteins are “_______” to their receptor proteins
lock and key - initiating infection
Both the ____ and ______ of a virus are antigenic, meaning that it causes an immune response triggered from antigens on the virus
capsid
envelope
What is the capsid made of?
glycoproteins - capsomeres
T/F: All viruses have an outer envelope
FALSE
What is the function of a capsid?
protect the fragile nucleic acid genome from:
physical damage
chemical damage
enzymatic damage
protein subunits
What are some properties of viruses?
heat sensitive
pH sensitivity
lipid solvents
chemicals
radiation and UV light
humidity
T/F: Enveloped viruses are generally less sensitive to lipid solvents and heat
FALSE - more sensitive
What are the 4 types of virus capsids?
isometric (icosahedral)
helical
complex
filamentous
What’s an example of an icosahedral capsid?
herpes virus
What is the structure of icosahedral capsid?
constructed of 20 equilateral triangular faces
What is the structure of a helical capsid?
tubular construction with the subunits arranged around the nucleic acid in a coil
What are examples of helical capsids?
rabies
flu
coronaviruses
What are the 2 symmetrical types of capsids?
icosahedral
helical
What are the 2 unsymmetrical capsid structures?
complex
filamentous
What are examples of complex viruses?
small pox
phage
What are filamentous viral capsid structures?
pleomorphic (able to assume different forms)
What’s an example of a filamentous capsid viral disease?
ebolavirus
What is the family of viruses?
(-viridae)
What is the genera of viruses?
(-virus)
What is viral taxonomy based on?
morphology of vision, capsid, and envelope
genome (RNA, DNA, SS, DS, etc)
serological relationships (serotypes)
replication strategy
Coronaviridae is a [double/single]-stranded, [enveloped/unenveloped], [helical/icosohedral] [RNA/DNA] virus
single
enveloped
helical
RNA
Capsomeres are assembled from ______ and these can now be crystalized and studied for ________
proteins
receptor binding (spike proteins)
________ are specific to host cell receptors
Capsid proteins
Capsid structural proteins are important for what?
viral stability and attachment
What are non-structural proteins (functional)?
enzymes involved in viral replication
_______ are generally formed against the structural proteins
Antibodies
How do antibodies being found against non-structural proteins help?
can help in differentiating animals vaccinated with inactivated recombinant vaccines, from those naturally infected (DIVA principle)
What are the capsid and envelope responsible for?
recognition of the host cell (receptor binding)
The capsid and envelope initially take the form of binding a specific _______ to a _________
virus-attachment protein to a
cellular receptor molecule
What are the 7 classes of viral genomes?
dsDNA
ssDNA
dsRNA
-ssRNA
+ssRNA
ss+RNA (retrovirus)
gapped dsDNA
= +mRNA
What is a promiscuous virus?
capable of infecting several species (like rabies)
What is a plastic virus?
exhibiting adaptability to change or variety in the environment (like influenza)
SARS-CoV-2 (Coronavirus) is [plastic/promiscuous]
promiscuous - any mammal with ACE 2 receptor is susceptible
What is a strain?
a well-characterized virus
What is virulence?
different strains possessing different properties
What is an isolate?
refers to the virus recovered from a specific host or location
What is a serotype?
generally means that immunity is NOT conferred by previous exposure to a different type
What are the 4 main groupings of viruses on the basis of epidemiological criteria?
enteric viruses
respiratory viruses
arboviruses
oncogenic viruses
What are arboviruses?
“arthropod-born viruses” replicate in their hematophagous arthropod hosts and are then transmitted by bite to vertebrate hosts
T/F: Viruses must replicate in living
TRUE
T/F: All cells will support replication of particular viruses
FALSE - not all do
Both viruses and cells have _____ and an affinity (_______) between them that results in attachment
receptors
complementarity
In the 1930s, _____ was used to titrate influenza virus. Since the 1950s, ______ have been used
embryonated egg
cell cultures
What does syncytia mean?
giant cells
What are cytopathic effects in cell culture?
- cells pile up, losing the property of inhibition and thus form giant cells or syncytia
- form inclusions in the cytoplasm or nucleus
- die
What does cytopathic cell mean?
kill cell becoming the host
T/F: All cells are cytopathic (will kill the host)
FALSE
example: Bovine Viral Diarrhea (BVD), virus is present and replicating but cells look normal
What happens in a persistent, productive viral infection?
no cytopathic effect: little metabolic disturbance
cells continue to divide
may be loss of the special functions of some differentiated cells
What happens in a transformation viral infection?
alteration in cell morphology
cells can be passaged indefinitely
What is a plaque assay? What do you do in this?
area with cells: blue (due to staining)
area with white: where virus grew and killed cells
count the plaques in the highest dilutions - “plaque-forming units” or “pfu/mL”
What is a quantitative assays of viruses - tissue culture infective dose 50?
virus titration experiments which can be used to quantify virus titers by investigating the cytopathic effects of a virus on an inoculated host cell culture4
compared to the widely used plaque assays, TCID50 assays offer the advantage that even viruses that do not form plaques or infect cell monolayers can be quantified.
What is quantitative assays of viruses - tissue vulture infective dose 50 used for?
characterize strain by measuring virulence
used when quantity of virus at various steps is important
producing vaccines
T/F: Viruses can also be grouped based on epidemiological criteria, such as clinical presentation
TRUE
_________ can measure the infectivity of viral particles through quantitative assays that observe cytopathic effects in cell cultures
Laboratories
T/F: The steps of DNA and RNA replication for viruses is completely different
FALSE - however, the mechanism of replication differs significantly
