BIOC20 - Virology Exam Latest Update
Where can viruses spread - ANSWER cell to cell and host to host, can spread across
species barriers
can infect all life forms
What is DNA/ RNA needed for in a virus - ANSWER - replication and expression of viral
genome
- packaging and delivery of the genome to more hosts
- modifying host structure to enhance replication
virion - ANSWER complete virus particle outside the host cell
what essential functions do viruses lack - ANSWER - synthesis of basic biological
molecules
- generation of ATP
- protein synthesis machinery
virion consists of - ANSWER - nucleic acid genome
- protective protein coat (capsid)
- some may also have lipid envelope
how do viruses release genetic material into host - ANSWER inside host cells, virus
particles disintegrate and release their genetic material.
major characteristics used for virus classification - ANSWER - type of genome
- symmetry of capsid
- presence or absence of an envelope
- dimensions
issues that arise with having an RNA genome - ANSWER - mRNA must be synthesized
from an RNA template
- RNA genome must be replicated
do viruses encode their own RNA polymerases - ANSWER Most of them do
Retroviruses - ANSWER have an RNA genome which gets converted to DNA by the host
cell using reverse transcriptase
,the DNA copy is then inserted into the DNA of the host cell
how were viruses distinguished from other microorganisms - ANSWER by filtration
first study to show that viruses exist - ANSWER Tobacco Mosaic Virus
why are bacteriophages used as a model system for viruses - ANSWER small simple and
easy to grow
use of plaque assay - ANSWER to quantify viruses
how do plaque assays work - ANSWER - phage binds to bacterial cells
- replicates and releases progeny
- repeated cycles lead to lysing of cells in the area surrounding infection
- observed as a clear plaque against uninfected cells
how are plaques counted - ANSWER using plaque forming units
what kind of eukaryotes are used in plaque assay - ANSWER in vitro cultures of
eukaryotes can be used
how are eukaryotic plaque assays visualized and why - ANSWER plaques are visualized
by staining the cells, since dead cells dont stain well
this needs to be done because eukaryotes grow in monolayers and therefore light
doesnt get diffracted as much
why are RBCs used for assaying viruses - ANSWER - visible due to color
- can be isolated and stored easily
- have carbohydrate containing receptors on their surface, which allow animal viruses
to bind
hemagglutination assay - ANSWER binding of excess virus which results in RBC
agglutination (clumping)
why does agglutination by viruses occur - ANSWER virus particles form bridges
between adjacent cells (clumps)
one hemagglutinating unit - ANSWER highest dilution of virus that agglutinates a given
aliquot of cells
approx 10^5 virus particles for 10^ RBCs
limitations to hemagglutination assay - ANSWER - sensitive to conditions such as
temperature, pH, buffer composition etc.
- some viruses only cause agglutination in one particular species
,process of visualizing viruses through electron microscopy - ANSWER - viruses are
mixed with an electron dense stain
- viruses don't take up the stain
- background is stained (negative staining)
- count no. of viruses in a given area.
reasons for why the ratio of physical virus particles to infectious particles, might be
greater than one - ANSWER due to defective particles
- disrupted or defective virions
- empty capsids (no genetic material)
- defective genomes (mutations/ deletions)
- cellular anti-viral defenses
- Latent infections (dont reproduce until right conditions)
how are viral replication cycles studied - ANSWER by infecting 10^3 - 10^6 cells to get
enough viral genetic material and proteins
how are all cells infected at the same time to synchronize replication - ANSWER infect
with excess virus to ensure that each cell receives one infectious particle
Multiplicity of Infection (MOI) - ANSWER No. of infectious particles per susceptible cell
normally used MOI is 10-100 PFU.
limitation in MOI method - ANSWER steps in replication cycle overlap, makes it difficult
to study
how to calculate MOI - ANSWER no of viral particles/ no of cells
unit: pfu/ cell
polyomavirus - ANSWER assembled in nucleus and not released till after cell death
, when analyzing virus replication cycle, why might there be an initial drop in infectious
titer? - ANSWER - defective particles
- uncoating inside the host cell
methods used for studying virus replication cycle - ANSWER - radiotracers
- antibodies against specific proteins
- molecular hybridization (labelled DNA or RNA probes)
- PCR
- Gel electrophoresis
- Microscopy
Virus replication cycles vary based on - ANSWER - host cell type
- viral genome
- complexity of virus
steps of virus replication - ANSWER - recognize and bind to a host
- enter host cell or insert genetic material
-viral genome is copied and proteins are made
- genome is enclosed by capsid proteins
- complete virus particle is released.
binding of virus to host cell - ANSWER - can be specific or non specific binding
- generally binds to a non-specific primary receptor followed by a specific secondary
receptor
how do RNA viruses replicate - ANSWER RNA viruses must encode RNA dependent RNA
polymerase (except retroviruses)
Where can viruses spread - ANSWER cell to cell and host to host, can spread across
species barriers
can infect all life forms
What is DNA/ RNA needed for in a virus - ANSWER - replication and expression of viral
genome
- packaging and delivery of the genome to more hosts
- modifying host structure to enhance replication
virion - ANSWER complete virus particle outside the host cell
what essential functions do viruses lack - ANSWER - synthesis of basic biological
molecules
- generation of ATP
- protein synthesis machinery
virion consists of - ANSWER - nucleic acid genome
- protective protein coat (capsid)
- some may also have lipid envelope
how do viruses release genetic material into host - ANSWER inside host cells, virus
particles disintegrate and release their genetic material.
major characteristics used for virus classification - ANSWER - type of genome
- symmetry of capsid
- presence or absence of an envelope
- dimensions
issues that arise with having an RNA genome - ANSWER - mRNA must be synthesized
from an RNA template
- RNA genome must be replicated
do viruses encode their own RNA polymerases - ANSWER Most of them do
Retroviruses - ANSWER have an RNA genome which gets converted to DNA by the host
cell using reverse transcriptase
,the DNA copy is then inserted into the DNA of the host cell
how were viruses distinguished from other microorganisms - ANSWER by filtration
first study to show that viruses exist - ANSWER Tobacco Mosaic Virus
why are bacteriophages used as a model system for viruses - ANSWER small simple and
easy to grow
use of plaque assay - ANSWER to quantify viruses
how do plaque assays work - ANSWER - phage binds to bacterial cells
- replicates and releases progeny
- repeated cycles lead to lysing of cells in the area surrounding infection
- observed as a clear plaque against uninfected cells
how are plaques counted - ANSWER using plaque forming units
what kind of eukaryotes are used in plaque assay - ANSWER in vitro cultures of
eukaryotes can be used
how are eukaryotic plaque assays visualized and why - ANSWER plaques are visualized
by staining the cells, since dead cells dont stain well
this needs to be done because eukaryotes grow in monolayers and therefore light
doesnt get diffracted as much
why are RBCs used for assaying viruses - ANSWER - visible due to color
- can be isolated and stored easily
- have carbohydrate containing receptors on their surface, which allow animal viruses
to bind
hemagglutination assay - ANSWER binding of excess virus which results in RBC
agglutination (clumping)
why does agglutination by viruses occur - ANSWER virus particles form bridges
between adjacent cells (clumps)
one hemagglutinating unit - ANSWER highest dilution of virus that agglutinates a given
aliquot of cells
approx 10^5 virus particles for 10^ RBCs
limitations to hemagglutination assay - ANSWER - sensitive to conditions such as
temperature, pH, buffer composition etc.
- some viruses only cause agglutination in one particular species
,process of visualizing viruses through electron microscopy - ANSWER - viruses are
mixed with an electron dense stain
- viruses don't take up the stain
- background is stained (negative staining)
- count no. of viruses in a given area.
reasons for why the ratio of physical virus particles to infectious particles, might be
greater than one - ANSWER due to defective particles
- disrupted or defective virions
- empty capsids (no genetic material)
- defective genomes (mutations/ deletions)
- cellular anti-viral defenses
- Latent infections (dont reproduce until right conditions)
how are viral replication cycles studied - ANSWER by infecting 10^3 - 10^6 cells to get
enough viral genetic material and proteins
how are all cells infected at the same time to synchronize replication - ANSWER infect
with excess virus to ensure that each cell receives one infectious particle
Multiplicity of Infection (MOI) - ANSWER No. of infectious particles per susceptible cell
normally used MOI is 10-100 PFU.
limitation in MOI method - ANSWER steps in replication cycle overlap, makes it difficult
to study
how to calculate MOI - ANSWER no of viral particles/ no of cells
unit: pfu/ cell
polyomavirus - ANSWER assembled in nucleus and not released till after cell death
, when analyzing virus replication cycle, why might there be an initial drop in infectious
titer? - ANSWER - defective particles
- uncoating inside the host cell
methods used for studying virus replication cycle - ANSWER - radiotracers
- antibodies against specific proteins
- molecular hybridization (labelled DNA or RNA probes)
- PCR
- Gel electrophoresis
- Microscopy
Virus replication cycles vary based on - ANSWER - host cell type
- viral genome
- complexity of virus
steps of virus replication - ANSWER - recognize and bind to a host
- enter host cell or insert genetic material
-viral genome is copied and proteins are made
- genome is enclosed by capsid proteins
- complete virus particle is released.
binding of virus to host cell - ANSWER - can be specific or non specific binding
- generally binds to a non-specific primary receptor followed by a specific secondary
receptor
how do RNA viruses replicate - ANSWER RNA viruses must encode RNA dependent RNA
polymerase (except retroviruses)
