BIOC20 – VIROLOGY EXAM
QUESTIONS COMPLETE WITH 100%
CORRECT ANSWERS
\.Where can viruses spread - ANSWERS-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 - ANSWERS-- replication and expression
of viral genome
- packaging and delivery of the genome to more hosts
- modifying host structure to enhance replication
\.virion - ANSWERS-complete virus particle outside the host cell
\.what essential functions do viruses lack - ANSWERS-- synthesis of basic biological
molecules
- generation of ATP
- protein synthesis machinery
\.virion consists of - ANSWERS-- nucleic acid genome
,- protective protein coat (capsid)
- some may also have lipid envelope
\.how do viruses release genetic material into host - ANSWERS-inside host cells,
virus particles disintegrate and release their genetic material.
\.major characteristics used for virus classification - ANSWERS-- type of genome
- symmetry of capsid
- presence or absence of an envelope
- dimensions
\.issues that arise with having an RNA genome - ANSWERS-- mRNA must be
synthesized from an RNA template
- RNA genome must be replicated
\.do viruses encode their own RNA polymerases - ANSWERS-Most of them do
\.Retroviruses - ANSWERS-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 - ANSWERS-by
filtration
,\.first study to show that viruses exist - ANSWERS-Tobacco Mosaic Virus
\.why are bacteriophages used as a model system for viruses - ANSWERS-small
simple and easy to grow
\.use of plaque assay - ANSWERS-to quantify viruses
\.how do plaque assays work - ANSWERS-- 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 - ANSWERS-using plaque forming units
\.what kind of eukaryotes are used in plaque assay - ANSWERS-in vitro cultures of
eukaryotes can be used
\.how are eukaryotic plaque assays visualized and why - ANSWERS-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 - ANSWERS-- 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 - ANSWERS-binding of excess virus which results in RBC
agglutination (clumping)
\.why does agglutination by viruses occur - ANSWERS-virus particles form bridges
between adjacent cells (clumps)
\.one hemagglutinating unit - ANSWERS-highest dilution of virus that agglutinates
a given aliquot of cells
approx 10^5 virus particles for 10^ RBCs
\.limitations to hemagglutination assay - ANSWERS-- 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 - ANSWERS-- 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 - ANSWERS-due to defective particles
QUESTIONS COMPLETE WITH 100%
CORRECT ANSWERS
\.Where can viruses spread - ANSWERS-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 - ANSWERS-- replication and expression
of viral genome
- packaging and delivery of the genome to more hosts
- modifying host structure to enhance replication
\.virion - ANSWERS-complete virus particle outside the host cell
\.what essential functions do viruses lack - ANSWERS-- synthesis of basic biological
molecules
- generation of ATP
- protein synthesis machinery
\.virion consists of - ANSWERS-- nucleic acid genome
,- protective protein coat (capsid)
- some may also have lipid envelope
\.how do viruses release genetic material into host - ANSWERS-inside host cells,
virus particles disintegrate and release their genetic material.
\.major characteristics used for virus classification - ANSWERS-- type of genome
- symmetry of capsid
- presence or absence of an envelope
- dimensions
\.issues that arise with having an RNA genome - ANSWERS-- mRNA must be
synthesized from an RNA template
- RNA genome must be replicated
\.do viruses encode their own RNA polymerases - ANSWERS-Most of them do
\.Retroviruses - ANSWERS-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 - ANSWERS-by
filtration
,\.first study to show that viruses exist - ANSWERS-Tobacco Mosaic Virus
\.why are bacteriophages used as a model system for viruses - ANSWERS-small
simple and easy to grow
\.use of plaque assay - ANSWERS-to quantify viruses
\.how do plaque assays work - ANSWERS-- 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 - ANSWERS-using plaque forming units
\.what kind of eukaryotes are used in plaque assay - ANSWERS-in vitro cultures of
eukaryotes can be used
\.how are eukaryotic plaque assays visualized and why - ANSWERS-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 - ANSWERS-- 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 - ANSWERS-binding of excess virus which results in RBC
agglutination (clumping)
\.why does agglutination by viruses occur - ANSWERS-virus particles form bridges
between adjacent cells (clumps)
\.one hemagglutinating unit - ANSWERS-highest dilution of virus that agglutinates
a given aliquot of cells
approx 10^5 virus particles for 10^ RBCs
\.limitations to hemagglutination assay - ANSWERS-- 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 - ANSWERS-- 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 - ANSWERS-due to defective particles
