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Life 205 Chpt.13
Viruses, Viroids, and Prions
91
Microbiology
Undergraduate 2
03/11/2013

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Term
This is a virus that infects a bacteria
Definition
bacteriophage (often shortened to Phage)
Term
Why are viruses difficult to study?
Definition
B/c they are obligate intracellular parasites. (They require another living organism as a host) and they are tiny.
Term
A nucleic acid surrounded by a protein coat.
Definition
a virion
Term
The protein coat of viruses
Definition
a capsid
Term
The nucleic acid together with the protein coat is called a ________.
Definition
nucleocapsid
Term
Viruses that do not have an envelope.
Definition
naked viruses
Term
How are enveloped viruses different than naked viruses?
Definition
In general, enveloped viruses are more susceptible to disinfectants because they damage the envelope and the virus becomes non-infectious.
Term
Most phages are what type of virus?
Definition
Naked
Term
What are three ways that viruses can be transmitted from one organism to another?
Definition
sexual contact,enteric(oral/fecal) respitory or salivary, vector(arthropods)(e.g. tics)(zootonic)
Term
Viruses so named because they are spread by mosquitos, ticks, and sandflies
Definition
arboviruses
Term
These phages exit the host cell by causing it to lyse at the end of an infection cycle.
Definition
Lytic (virulent) phages
Term
Viral infections that result in new virus particles
Definition
productive infections
Term
What are the five phases of the infection cycle of virulent phages?
Definition
1. attachment
2. genome entry
3. synthesis of proteins and genome
4. Assembly(maturation)
5. Release
Term
These phages have the option of either directing lytic or lysogenic infections
Definition
temperate phages
Term
In this type of infection, viral DNA is incorporated into the host cells' genome
Definition
lysogenic infection
Term
A change in the phenotype of a lysogen as a consequence of the specific prophage it carries.
Definition
Lysogenic conversion
Term
Why is lysogenic conversion inportant from a medical standpoint?
Definition
Strains of typical bacteria begin producing toxins that would not be produced by the cell otherwise.
This increases the pathogenicity of certain strains of bacteria.
Term
This type of transduction results from a packaging error during phage assembly. Short DNA fragments can be mistakenly packaged into the phage head during assembly.
Definition
generalized transduction
Term
A phage head that contains only bacterial genes in place of phage genes cannot direct a phage replication. these are called what?
Definition
generalized transducing particles
Term
This type of transduction results from an excision mistake made by a temperate phage during its transition from the lysogenic to the lytic cycle.
Definition
Term
What are the 3 main shapes of viruses?
Definition
Icosohedral, helical, and complex
Term
What type of virus cause productive infections, but do not kill the host cell?
Definition
filamentous
Term
What would be the main cause of a temperate phage remaining in the lysogenic phase?
Definition
Low nutrition usually means the virus will stay in the lysogenic cycle
Term
What is the phage both prevents and maintains the lysogenic state?
Definition
A repressor protein
Term
How does the repressor protein both prevent and maintain the lysogenic state?
Definition
It doesn't allow another phage to enter the cell, but it keeps the one already there in the lysogenic state.
Term
If the DNA of a cell in the lysogenic state is damaged, what happens?
Definition
The SOS repair system will activate protease, the protease destroys the repressor, the prophage will be excised (enter the lytic cycle)
Term
What is one way to count phages?
Definition
Plaque assay (circular zones of clearing due to cell lysis caused by the phage)
Term
What is one way we could possibly target viruses with antiviral drugs?
Definition
Virus replication depends a lot on virally encoded enzymes...they are a good target for antiviral drugs.
Term
What is the 5 step infection process of animal virus replication?
Definition
1. attachment
2. penetration and uncoating
3. synthesis
4. assembly
5. release
Term
What is the main difference between generalized and specialized transduction?
Definition
In specialized transduction, only the bacterial genes adjacent to the integrated phage DNA can be transferred. In general transduction, any gene of the donor may be transferred.
Term
In what way do bacteria defend themselves against phages by deterring attachment of the phage?
Definition
THey cover the receptor on the cell surface so the virus cannot attach
Term
These protect bact
Definition
Term
These protect bacteria from phage infection by quickly degrading incoming foreign DNA by using restriction and modification enzymes.
Definition
Restriction-modification system
Term
What is one tool scientists use to remove genes from one DNA molecule and join them to another?
Definition
restriction enzymes
Term
How does the bacteria protect its own DNA from degradation by restriction enzymes?
Definition
It methylates its own DNA, and only DNA that is unmethylated(phage DNA) will be destroyed.
Term
CRISPR stands for what?
Definition
Clusters of Regularly Interspersed Short Palindromic Repeats
Term
A chromosomal region in the bacterial cell that holds spacer DNA
Definition
CRIPSR
Term
What is the benefit of CRISPR?
Definition
It holds a historical record of phage infections, allowing bacteria and its progeny to block subsequent infections by the same phage.
Term
The concentration of infectious phage particles in the original phage solution
Definition
titer
Term
in absorption, the attachment of what triggers endocytosis?
Definition
Attachment to receptors
Term
What are the two main methods of viral entry? (absorption)
Definition
Endocytosis and membrane fusion
Term
What do viruses usually bind to on the outer cell wall?
Definition
specific receptors , glycoproteins on the plasma membrane (often more than one required)
Term
Why can most viruses only infect a certain species?
Definition
because they bind to specific receptors not usually found in every living animal
Term
In an _____ virus, the entire virion is taken into the cell.
Definition
animal virus
Term
IN this type of penetration and uncoating, the lipid envelope of the virion fuses with the plasma membrane of the host cell and releases the nucleocapsid directly into the cytoplasm.
Definition
membrane fusion
Term
In this type of penetration, the virion exploit normal cell receptor-mediated endocytosis to bring themselves into the cell.
Definition
endocytosis
Term
Where do most DNA viruses multiply in animal cells?
Definition
In the nucleus
Term
IN all viruses, the nucleic acid separeates from its protein coating prior to the start of replication, this is the process of _______.
Definition
uncoating
Term
What two distinct, but interrelated events must occur for the synthesis of viral proteins and replication of the genome?
Definition
1.) expression of viral genes to produce structural and catalytic proteins
2.) synthesis of multiple copies of the viral genome.
Term
What type of viruses use the host cells machinery for DNA synthesis?
Definition
DNA viruses
Term
What is the main difference btwn dsDNA virses and ssDNA viruses in replication?
Definition
The ssDNA must first make a template and then begin making copies.
Term
What type are most RNA viruses?
Definition
ssRNA
Term
Where do most ssRNA viruses replicate?
Definition
in the cytoplasm
Term
What does RNA replication require?
Definition
virally encoded RNA polymerase called replicase
Term
How is the replication of RNA viruses different from DNA viruses?
Definition
RNA viruses must synthesize RNA from an RNA template instead of a DNA template.
Term
Why do RNA viruses generally have higher rates of mutations, and why can this be beneficial for them?
Definition
The replicase (RNA virsu RNA polymerase) does not have proofreading ability=more mistakes. It can be beneficial because RNA viruses can adapt more quickly than DNA viruses.
Term
A type of antigenic variation that may cause a person whose immune system protected against one viral strain to not work against the next.
Definition
antigenic drift
Term
What type of enzyme do reverse-transcribing viruses for?
Definition
reverse transcriptase
Term
What does reverse transcriptase do?
Definition
synthesizes a DNA strand from an RNA strand.
Term
This kind of virus has a (+) RNA strand and carries reverse transcriptase with it.
Definition
retrovirus(HIV)
Term
In what way do most viruses release?
Definition
By budding.
Term
The process of a virus acquiring its envelope
Definition
budding
Term
Where does assembly take place in an animal virus?
Definition
In the nucleus or cytoplasm depending on the virus
Term
How does the virus obtain its viral envelope through budding?
Definition
The virus protein spikes insert themselves into specific regions of the host cells membrane. Matrix proteins accumulate on the inside surface of those regions. Assembled nucleocapsids then extrude from the cell becoming covered by a layer of matrix protein and lipid envelope in the process.
Term
Does budding cause cell death?
Definition
not necessarily. The membranes can be repaired after the viral particles exit.
Term
How are naked viruses released?
Definition
Many viruses trigger apoptosis prior to the release of viral particles.
Term
How do enveloped viruses exit the cell?
Definition
budding
Term
Why are virally encoded enzymes medically important?
Definition
Because they are important in many viral processes and can be targeted to stop the virus from infecting.
Term
What type of infection is characterized by a sudden onset of symptoms and a relatively short duration?
Definition
Acute infections
Term
This type of infection can continue for years or even life
Definition
persistent infection
Term
The silent viral genome
Definition
provirus
Term
genes that stimulate cell growth
Definition
proto-oncogenes
Term
Genes with similar DNA to proto-oncogenes that interfere with the cell's own control mechanisms.
Definition
oncogenes
Term
What are most tumors caused by?
Definition
Mutations in the host genes that regulate cell growth
Term
WHat is an example of a virus that is associated with the development of cancers?
Definition
HPV, EBV(epstein barr virus), HHV-8 (they appear to interfere with the function of an important tumor supressor gene)
Term
What are the most common viral causes of cancer?
Definition
DNA tumor viruses
Term
How can a vaccine prevent cervical cancer?
Definition
The vaccine would hopefully cause the individual to build up immunity to the virus HPV, so that it could not cause cancer
Term
What are some ways to study animal viruses?
Definition
1. innoculate live animals with the virus
2. cell culture (tissue culture)
Term
In this type of culture, animal cells are grown in a liquid medium contained in a special screw-capped flask
Definition
cell culture (also know as a tissue culture)
Term
tissue removed from an animal then processed to get individual cells
Definition
primary culture
Term
Distinct morphological alterations in infected cells.(cells may change shape, detach from surface, or lyse)
Definition
cytopathic effect
Term
a distinct region where the site of viral replication is
Definition
an inclusion body
Term
What is one of the most precise methods for determining the concentration of animal viruses in a sample?
Definition
A plaque assay
Term
How are plaque assays different from animal virus to bacteriophage?
Definition
A monolayer of tissue culture cells is the host instead of the broth with bacterial cells in it.
Term
How can the viral titer be estimated?
Definition
using a quantal assay
Term
in this method, several dilutions of the virus preparation are administered to a number of animals, cells, or chick embryos
Definition
quantal assay
Term
What is the titer of the virus?
Definition
the dilution at which 50% of the inoculated hosts are infected or killed.
Term
How do we measure the titer of the virus?
Definition
ID50: Infective dose
LD50: Lethal dose
Term
WHen red blood cells agglutinate (clump)
Definition
hemagglutination
Term
When does hemagglutination occur?
Definition
When individual viral particles attach to the surface molecules of multiple red blood cells simultaneously.
Term
What does hemagglutination show?
Definition
That there is a high concentration of viral particles in the blood
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