Transcript Virus

SI Session
Viruses, viroids, and prions
Fall 2009
For Dr. Wright’s Bio 27 Class
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http://micro.magnet.fsu.edu/cells/virus.htm
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Virus, Viroid, Prion
Supplemental instruction
Fall 2010
For Dr. Wright’s Bio 7/27 Class
Picture from: http://www.wiley.com/college/boyer/0470003790/cutting_edge/prions/prion1.gif
Designed by Pyeongsug Kim ©2010 [email protected]
Questions on viruses, viroids, and prions
<< Part I>>
What do we mean when we say a virus is lytic? Temperate? Can a cell shed virus but not itself be killed?
What two structures do all viruses have in common? Why do we say that a virus is not alive (i.e., what does it lack?) What do we
mean when we say a virus is enveloped? How does such a virus get out of the host cell? What do we mean when we say a virus is
naked?
Why would a temperate phage cause a lysogenic infection? What type of stimulus would cause it to become lytic again?
Give two examples of lysogenic conversion?
What is transduction?
What is a viroid made of? What types of organisms does it infect? How can viroid infection be controlled?
What is a prion made of? What types of organisms (and tissues within) does it infect? How can prion infection be controlled?
<< Part II>> (Not Yet) ..
What implications does this have for control of viral activity?
Are all virus genomes the same? What are some types of genomes seen in viruses but not cellular organisms?
How does a latent infection alter the genome of the host cell?
What are the stages of viral infection?
What is the cytopathic effect?
Why can measuring antibody levels indicate that an individual has been infected by a particular virus?
Compare and contrast acute, late, chronic and latent infections?
Give an example of a virus that causes each.
In which of these conditions does the person remain a carrier? (i.e., continue to produce infectious virus?)
Which of these can persist for a long time?
How are such diseases cured?
How can a virus cause tumors?
What type of gene is mutated to give rise to a tumor?
What are two ways that viruses can introduce such mutations?
Are most tumors caused this way?
In animals, viruses attach to specific receptors on host cells. There are no such receptors in plants. How, then, do viruses infect
plants?
-Dr. Wright’s Bio 27 Study guide. Fall 2009
Viruses
-Nonliving
-naked or enveloped
-have a protein capsid
-nucleic acid
~DNA or RNA, but not both
-need the host for replication
infect every living thing
Naked virus
-take over metabolism of the host cell
and kill it.
-Some virus live in harmony with their
hosts.
Enveloped virus
Picture from http://micro.magnet.fsu.edu/cells/virus.htm http://www.csa.com/discoveryguides/avian/images/virus.jpg
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Viroids
-Nonliving
Smallest particle able to replicate
-Naked; without protein coat.
-Nuclec acid
______
RNA only
-single viroid can infect cell
resistant to proteases and nucleases
-replicate autonomously
-Plant phathogens *as far as we know
Picture from http://vegetablemdonline.ppath.cornell.edu/photopages/Potatoes/Viruses/PotVirusFS3.htm http://www.gidabilimi.com/forum/58-genel-mikrobiyoloji/1892-viroidler
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Prions
-Nonliving; infectious _______
proteins
-No nucleic acid
neither DNA or RNA
-involved in human and mammalian prion diseases is called “PrP”
e.g. mad cow disease
-may be removed by autoclaving
__________.
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Viruses
-infect every living thing
-_____________
Bacteriophages(or shortly “phages”)
Viruses that infect bacteria.
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• Lytic
cycle
-Phage(the virus) injects its DNA
makes more phage
the cell lysis
(the bacteria bursts)
• Lysogenic cycle.
:be released from a cell, but not kill the cell.
-Phage(the virus) injects its DNA
-the DNA integrates into the bacaterium's DNA
-if the cell copies itself, the virus DNA is also copied with it.
-the DNA from the virus stays in the cell.
-used commonly as a genetic tool; DNA technology.
-Lysogenic conversion may occur.
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• Temperate phages.
-transfer DNA into the host cells
-multiplies either as plasmid or
integrated into the chromosome of
the host.
- Harmony with the bacteria.
-can either lyse their host or
replicate with it.
-lambda()
• Latent
infection
- show no sign that cell are infected.
- HIV infection
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Lambda()
- Temperate phage
- lysogenizes E. Coli
- Some of bacteria will be lysed,
other bacteria will be lysogenized.
Lytic if bacteria are actively dividing
Otherwise lysogenic.
- Prophage :integrated into host genome
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Picture from Dr. Wright’s Bio27 slide
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•________________
Lysogenic conversion
- When a cell becomes lysogenized,
phage DNA integrated into the
chromosome of the host.
 (occasionally) extra genes carried
by the phage get expressed in the cell.
change the properties of the
bacterial cell.(new strains)
- e.g. Toxins in C.botulism (Botulism)
*After virus infection, “good guy” may become “bad guy” through
lysogenic conversion or the other way around.
In the lab, lysogenic conversion is used for genetic engineering.
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Temperate,
Lysogenic,
Lysogenic conversion, Lytic,
Lytic
_________
Some phases lyse their host cells.
Lysogenic
_________ Some are extruded w/o killing the host.
Temperate Most live in harmony with them.
_________
Lysogenic
conversion The latter often code for gene products that
_________
confer new properties on the host.
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Transduction
_____________
-phage-mediated genetic transfer
-DNA can be transferred from on bacterial
cell to another.
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Transduction (cont’d)
1) Generalized
__________ transduction
- any bacterial gene can be
transferred
Specialized
2) __________
- virus inserted in a specific site
so only genes adjacent to it are
transferred (i.e., temperate phages)
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Genetic transfer from one bacterial cell to another.
Conjugation
__________
- Sex pili; Virus not involved.
Transduction
__________
- Generalized; Specialized.
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