1. Viruses, viroids, and prions For Dr. Wright’s Bio 27 ClassSI
Biology
SI Session
Viruses, viroids, and prions
Fall 2009
For Dr. Wright’s Bio 27 Class
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2. Supplemental instruction For Dr. Wright’s Bio 7/27 Class
Virus, Viroid, Prion
Supplemental instruction
Fall 2010
For Dr. Wright’s Bio 7/27 Class
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3. 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

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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
-take over metabolism of the host cell and kill it.
-Some virus live in harmony with their hosts.
Naked virus
Enveloped virus
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Viroids
-Nonliving
Smallest particle able to replicate
-Naked; without protein coat.
-Nuclec acid
______ only
-single viroid can infect cell
resistant to proteases and nucleases
-replicate autonomously
-Plant phathogens *as far as we know
RNA
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Prions
-Nonliving; infectious _______
-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 __________.
proteins
autoclaving
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Viruses
-infect every living thing
-_____________
Viruses that infect bacteria.
Bacteriophages(or shortly “phages”)
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cycle
-Phage(the virus) injects its DNA
makes more phage
the cell lysis
(the bacteria bursts)
Lytic
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.
Lysogenic
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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()
Temperate
infection
- show no sign that cell are infected.
- HIV infection
Latent
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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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________________
- 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)
Lysogenic conversion
*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.
_________ Some are extruded w/o killing the host.
_________ Most live in harmony with them.
_________ The latter often code for gene products that
confer new properties on the host.
Lysogenic
Temperate
Lysogenic conversion
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_____________
phage-mediated genetic transfer
DNA can be transferred from on bacterial cell to another.
Transduction
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Transduction (cont’d)
1) __________ transduction
- any bacterial gene can be transferred
2) __________
- virus inserted in a specific site
so only genes adjacent to it are transferred (i.e., temperate phages)
Generalized
Specialized
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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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