Final; Virus Biology Flashcards
What are the two theories of virus origin
cellular origin
autopoietic origin
This proposes that viruses were once cellular components but over time they evolved separately
cellular origin
This proposes that viruses, once autopoietic entities, became dependent on cells for replication
autopoietic origin
What are the attributes that viruses are classified on
particle structure genome replication features serology stability
What are the components of virus particle structure
composition
stucture
size
This is RNA or DNA in a core that is protected by a protein coat
nucleocapsid
A virus is defined by what
the nucleocapsid structure
What are the different nucleocapsid structures
helical
pleomorphic
icosahedral
A nucleocapsid is comprised of what
repeating protein subunits called capsomeres
This is a virus-modified cellular membrane acquired upon exit from the host
envelopes
This renders enveloped viruses noninfectious
exposure to lipid solvents in the laboratory
True or False
Enveloped viruses may have nucleocapsids with different structures
True
What are the lengths of the smallest and largest virus particle
smallest; 18nm
largest; 300nm
What are the different combinations of the viral genome
double or single stranded
DNA or RNA
What different types of single stranded RNA can you have
plus sense ssRNA
minus sense ssRNA
ambisense
Which type of ssRNA can be used directly for translation
plus sense
What must happen to minus sense ssRNA before translation
a positive (plus sense) copy must be made
What are the different structures (gene arrangement) of the viral genome
linear
circular
segmented
diploid
How can viruses not follow the central dogma
They are able to revert from RNA to DNA via reverse transcriptase
What do most DNA viruses need that RNA viruses do not
access to the nucleus
What do RNA viruses need that DNA viruses do not
the ability to make positive/negative strands
reverse transcriptase
What is the process of viral replication
attachment entry transcription translation replication assembly release
How does a virus attach to a cell
via receptors
the cell does not have viral receptors, the virus binds to already functional receptors on the cell
What type of cell receptors do viruses bind to
signaling
cell adhesion
transport
How to viruses attach to the cell receptors
do not mimic cell receptor ligands
typically spike like projections
may require co-receptor
This is a major determinant of virus tropism (host range)
attachment
True or False
Viruses are only specific to humans
False; viruses are known to infect essentially all forms of life
This is a major factor in eradication
host range
What are the pathways of viral entry
receptor mediated endocytosis
direct penetration of plasma membrane
How can non-enveloped viruses entry the cell
its not well understood
perhaps through pores or membrane disruption
In what ways can enveloped viruses enter the cell
membrane fusion
receptor conformational change (pH; receptor induced)
How does nuclear replication occur
the genome and remaining protein coat are transported to the nucleus to deliver the genome
How does cytoplasmic replication occur
genome is released into cytoplasm to site of replication
many RNA viruses replicate in MACs
dsRNA viruses never release what
their genomic material from the entering particle
DNA viruses rely on what for transcription
cellular RNA polymerases
The genome of what can serve was mRNA
+ssRNA
These RNA viruses must bring their own polymerases into the cell
-ssRNA
dsRNA
All viruses need what to produce proteins
the cells ribosomes
Non-structural proteins are only seen where
inside the infected cell
The order of genomic replication of viruses depends on what
virus genome
This induces innate immune response so the genome stays inside the particle
dsRNA
The dsRNA mRNA is synthesized where
inside the particle and is then transported to the cytoplasm
Why are poxviruses an exception to the DNA viruses needing access to the nucleus
virion contains the necessary RNA polymerase and the genome encodes the DNA polymerase for replication
What is the function of viral assembly
to package new genomes into functional particles
What aids in assembly
localized structural proteins; cellular viral “factories”
the genome contains packaging signals
How does an adenovirus undergo assembly
empty protein coat imports genome
How does a reovirus undergo assembly
RNA packaged during capsid assembly
How does a retrovirus undergo assembly
reassembly on a membrane
What are the different types of viral releases
lysis
weak lysis (impair membrane repair)
budding (enveloped only)
What are the kinetic phases of viral replication
eclipse; attachment and uptake
exponential growth; replication and assembly
plateau; cell death
True or False
There is a variety of the length of time it takes for a virus to go from the start on an infection to the beginning of a plateau
True;
bacteriophage; 30 mins
vaccina; 24 hours
What is the productivity of a virus
measure amplification
vesicular stomatitis virus (VSV) 1:1000
vaccina 1:100
What methods are used to initially discover a virus
disease in host
contaminant in cell culture
What methods are used to confirm a virus
purification
confirmation of disease; animals, eggs, or cell culture (preferred)
What are the principle of detection and quantification methods
infectivity
physical
genome
serological
These methods are useful for viruses that cannot be cultivated
molecular methods
What are four types of infection assays
cytopathic effect (CPE)
fluorescent focus assay
plaque assay
Infectious dose
What are two types of particle assays
electron microscopy
hemagglutinin assau
What are two types of genome assays
PCR
southern (DNA) and northern (RNA) blots
What are three types of serological assays
virus neutralization
enzyme linked immunosorbant assay (ELISA)
western (protein) blot
True or False
Different methods of viral detection and quantification give different answers
True
What is the average diameter of a human virus
30-300nm
