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54 Cards in this Set

  • Front
  • Back
What is the nature of the effective antibodies produced by a viral vaccine?
The antibodies are neutralizing antibodies. That is, the antibodies bind to locations on the virus that neutralize the infectivity.
What are the three types of viral vaccines?
1. Killed/chemically inactivated whole virus
2. Live, attenuated whole virus
3. Subunit vaccines (surface protein only)
Against what nine viruses are live vaccines available?
1. Measles
2. Mumps
3. Rubella
4. Varicella
5. Influenza
6. Yellow fever
7. Poliomyelitis (Sabin)
8. Rotavirus (Rotashield)
9. Variola
Against what five viruses are inactivated vaccines available?
1. Poliomyelitis (Salk)
2. Hepatitis B
3. Hepatitis A
4. Rabies
5. Influenza
Against what two viruses are subunit vaccines available?
1. Hepatitis B
2. Genital papilloma
List the five major characteristics of viruses, as described in Dr. Ou's handout.
1. Nucleoproteinic entities
2. Obligatory intracellular parasites
3. Potentially pathogenic
4. Genome is composed of either RNA or DNA but never both
5. Replicate directly from genetic material
What are the two elementary constituents of a virus?
Nucleic acids and proteins
Into what two categories are virus-coded proteins divided?
Virion proteins- structural (or rarely, involved in nucleic acid synthesis)

Nonvirion proteins- nonstructural, involved in nucleic acid synthesis
What is a capsid?
A capsid is a viral protein shell that surrounds nucleic acids.
Describe the two fundamental principles of virion structure.
1. Subunit composition: There is not enough viral genetic information to encode a protein large enough to form a complete viral shell, and it would be impossible to synthesize something so large without debilitating defects, so the virion is necessarily composed of smaller subunits.

Self-assembly: When subunits reach a critical concentration, they crystallize into their shell in a non-energy dependent manner.
Describe the structure of a helical virion capsid.
In a helical virion capsid, subunit proteins are arranged in a helix around an axis of symmetry along which translation occurs. The helical structure forms a tubular shell for nucleic acids.
Describe the structure of a cubic virion capsid.
In a cubic virion capsid, subunits are arranged in near-spherical, closed shells called icosahedrons. Strictly speaking, an icosahedron is composed of twenty equilateral triangular faces with twelve corners, comprised of sixty equivalent subunits. Most cubic viruses have more than sixty subunits and do not fit this exact definition.
How can larger numbers of subunits be accommodated by an icosahedral structure?
Larger numbers of subunits can be accommodated if you imagine the triangular faces of the icosahedron being divided into subtriangles, which have a subunit at each corner. Subunits may also form clusters of five or six called capsomers. The number of capsomers on a shell can be determined by
C=(T-1)x10+12,
where C=capsomers and T=subtriangles
What are naked viruses composed of?
Naked viruses are composed of only nucleic acid and protein capsid. This is also known as nucleocapsid.
What is the envelope of enveloped viruses composed of?

Describe the envelope structure.
The envelope is derived from a cellular lipid membrane, often the plasma membrane of the host cell. It therefore has the lipid bilayer structure of the cell. It has virus-coded glycoproteins extending through it, as well as cellular carbohydrates.

The envelope does not have a geometrical structure like the capsid. It may have an inner surface lining of non-glycosylated matrix protein that establishes a connection between envelope and capsid.
Describe the two methods of viral classification. Which do we use?
1. Horne-Lwoff-Tournier (HLT) classifies based on:
a. RNA vs. DNA
b. Helical vs. cuboidal symmetry
c. Naked vs. enveloped virion
This is the method we use.
2. Baltimore classifies based on virus replicative strategy.
What is the most frequently used virological assay?
ELISA/EIA is used most frequently.

For viral ELISA, the wells of a microtiter plate are coated with antibody to a viral capsid protein. The patient samples are added to the plate and incubated to allow the antibodies to capture viral particles. The plate is then washed and a second virus-specific antibody, conjugated to a reporter enzyme, is added to the plate and incubated. The plate is then washed again and activity of the reporter enzyme is used to assay the amount of viral particles bound to the plate.
Name and briefly describe the less commonly used assays to diagnose viruses.
1. Electron microscopy: direct visualization of viral particles
2. Hemagglutination: aggregation of RBCs can be caused by coat proteins of certain viruses
3. Viral enzyme assays: Some enzymes carry specific enzymes for which enzyme activity can be measured
4. Polymerase chain reaction (PCR): PCR with primers for a nucleic acid sequence specific to a certain viral genetic code can be done to assay for the presence or copy number of a viral genome in blood samples
5. Plaque assay: Cells growing in a petri dish can be infected with a virus and overlaid with agar. If the virus used for infection is lytic, then the infected cells will dye and can be visualized with a red dye. The empty, lysed area is called a plaque.
What is an arbovirus?
An arbovirus is a virus transmitted by an arthropod vector.
Give an example of a naked, icosahedral, positive-stranded RNA virus.
Poliovirus
What are the five stages of the poliovirus growth cycle?
1. Adsorption
2. Penetration
3. Eclipse
4. Maturation
5. Release
Describe the physical requirements for adsorption of poliovirus to the cell surface.
Adsorption of poliovirus is temperature independent, but requires favorable salt and pH conditions, as the interaction between virus and cell is electrostatic.
Describe the concept of tissue tropism.
Tissue tropism is a term describing the specificity of a virus for certain tissues based on its specificity for certain cell receptors that may only be expressed in those tissues.
For what tissues does poliovirus exhibit tissue tropism?
Polivirus exhibits tissue tropism for spinal cord and intestinal tissues, in which it replicates in vivo.
Why does tissue tropism not apply in cell culture?
Tissue tropism does not apply in cell culture because receptor expression may be de-repressed in cells from a tissue which would normally repress expression of a specific receptor.
Describe the mechanism of genome injection in animal viruses.
Animal viruses do not have a mechanism for genome injection, only bacterial viruses do. Animal viruses are dependent on cellular uptake activity.
Describe the factors important for penetration of the poliovirus into the cell.
Cellular entry is temperature-dependent. The VP4 capsid protein appears to be important becaues of the fatty acid attached at its N-terminus, which may interact with the host cell membrane.
What percent of polioviruses successfully adsorb, penetrate, and uncoat to initiate infection?
2%
Describe the eclipse period of viral infection.
The eclipse period occurs after the virus has uncoated within the cell. There is no evidence of virus within lysed cells because the virion has dissociated and the viral genome has yet to be transcribed for viral replication.
How does the nucleus participate in polioviral replication?
It doesn't.
How does mature poliovirus leave the cell?
Eventually, the cell disintegrates and liberates all of the progeny virions. This mechanism is typical of naked viruses.
What viral group do influenza viruses belong to?

What does the prefix myxo- mean?
Orthomyxoviruses

Myxo- means mucus
Name an orthomyxovirus.
Influenza virus is an orthomyxovirus.
Name four paramyxoviruses.
1. Mumpsvirus
2. Measlesvirus
3. Parainfluenza virus
4. Respiratory syncytial virus
To what viral group do mumpsvirus, respiratory syncytial virus, measlesvirus and parainfluenza virus belong?
Paramyxovirus
What three illnesses are caused by mumpsvirus?
1. Salivary gland infections
2. Aseptic meningitis
3. Orchitis (infection of the testes)
What two illnesses are caused by measlesvirus?
1. Measles (rubeola)
2. Subacute sclerosing panencephalitis (SSPE)
What two illnesses are caused by parainfluenza viruses?
1. Pneumonitis
2. Pharyngitis
What is the major member of the rhabdovirus group?

What does the prefix rhabdo- mean?
Rabiesvirus belongs to the rhabdovirus group.

Rhabdo- means rod-shaped.
Name two bunyaviruses.
1. California encephalitis virus
2. Hantavirus
Name three arenaviruses.
1. Lassa virus
2. Machupo (Bolivian hemorrhagic fever)
3. Lymphocytic choriomeningitis virus
To what viral group do lassa virus, machupo, and lymphocytic choriomeningitis virus belong?
Arenavirus
Name two filoviruses.
1. Ebola virus
2. Marburg virus
To what viral group do Ebola and Marburg viruses belong?

Why is the group named as it is?
Ebola and Marburg viruses are filoviruses. They are called filoviruses because they are filament-shaped.
Describe the genome of influenzavirus.
The influenzavirus genome is a single negative strand of RNA. It is composed of eight segments that are essential for infectivity.
Describe the function of hemagglutinin on the influenzavirus surface.
Hemagglutinin facilitates the binding of influenza viruses to N-acetylneuraminic acid on the cell surface.
Describe the function of neuraminidase on the influenzavirus surface.
Neuaminidase helps the influenzavirus to release from the cell.
Describe the capsid structure and envelopment state of the influenzavirus.
Influenza virus has a helical capsid and is enveloped.
What lines the inner surface of the influenzavirus viral envelope?
Nonglycosylated matrix protein lines the inner surface of the viral envelope.
How are influenzavirus HA and NA proteins different from cell surface proteins?
HA and NA are anchored in the matrix proteins below and are not laterally mobile.
Describe the penetration process that the influenzavirus goes through.
The influenzavirus enters the cell via a clathrin-coated pit. Its envelope fuses with the membrane of its endosome/lysosome, releasing the viral capsid into the cytoplasm.
What is primary transcription?
Primary transcription is the process by which a negative-stranded RNA virus first synthesizes mRNA from its genome with the viral RNA polymerase that is packaged within the virion. The mRNA is synthesized as separate monocistronic fragments.
Where are influenzavirus proteins synthesized?
Influenzavirus proteins are synthesized on free ribosomes because they are not glycosylated.
Describe replication in negative-stranded RNA viruses.
A complete positive-stranded RNA is synthesized by viral polymerases, to serve as a template for negative strand replication. These positive strands are used multiple times as templates to synthesize the negative-stranded genome.