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