Virology Flashcards
Viruses cause ___% of human illness
80%
Can obligate intracellular parasites live outside a cellular host?
No
Can obligate intracellular parasites be treated or cured?
No, not with existing medical therapies
What are the smallest known pathogens?
Viroids
What are viroids? How do they replicate?
Naked, circular, single-stranded RNA molecules that do not encode protein yet replicate autonomously when introduced into host plants
A viral particle is a…
virion
What does a virion’s structure consist of?
- Protein coat
- Nucleic acid core
- Envelope (occasionally)
In a laboratory setting, what are the three ways to replicate viruses?
- Cell culture
- Fertilized eggs
- Living animals
Each virus capsid consists of…
identical protein units called capsomeres
The protein coat surround the nucleic acid core is called…
a capsid
Capsomeres bond together and give the capsid…
symmetry
What are the two basic patterns of self assembly of virus capsids?
- Helical symmetry
- Icosahedral symmetry
What is helical symmetry of a capsid?
Protein subunits and nucleic acid are arranged in a helix
What is icosahedral symmetry of a capsid?
Protein subunits assemble into a symmetric shell that covers the nucleic acid containing core
Viruses are characterized by their…
nucleic acid cores
The DNA and RNA is a virus’ core can be ___ or ___
ds (double stranded) or ss (single stranded)
If genetic information is used within a cell to produce the proteins needed for the cell to function, what is occurring?
Expression
Cell metabolizes and grows
If genetic information is being transferred horizontally between cells of the same generation, what is occurring?
Recombination
Recombinant cell with new combinations of genes
If genetic information is being transferred vertically to the next generation of cells, what is occurring?
Replication
Offspring cells produced
What is the most stable viral form/genome?
dsDNA genome
What is an example of a virus with dsDNA genome?
Herpesviridae
What viral form/genome is most prone to mutation?
+ssRNA genome
What is an example of a virus with +ssRNA genome?
Ebola virus
Many viruses that infect mammals are…
enveloped
All envelopes have…
a phospholipid bilayer
Envelopes arise from…
the plasma membrane of the infected host cell
If a virus does not have an envelope, how is it classified?
Naked
Is adenovirus naked or enveloped?
Naked
Is herpesvirus naked or enveloped?
Enveloped
After a virion enters a host cell, its DNA is…
uncoated
Once virion DNA is uncoated, a portion is transcribe, producing…
mRNA that encodes “early” viral proteins
What occurs during biosynthesis of the virus?
Viral DNA is replicated and some viral proteins are made
In late translation, ___ are synthesized
capsid proteins
Once virions are mature, they are…
released
What is a lytic infection?
Host cell fills with virions and bursts resulting in cell death
What are the six steps of lytic infection?
- Attachment
- Penetration
- Uncoating
- Biosynthesis
- Maturation
- Release
What is viral tropism?
Virus binds to specific receptors on host cell
Some virions require ___ for successful attachment to a host cell
co-receptors
What are the steps of virion penetration?
- Adhesion of virus to host receptors
- Engulfment into vesicle
- Viral RNA is released from vesicle
What is uncoating and where can it occur?
Removal of the capsid happens:
* at plasma membrane
* in the cytoplasm
* at the nuclear membrane
After uncoating of viral DNA, ___ makes a DNA copy of the RNA, then uses the new DNA as a template to make complementary DNA strand.
reverse transcriptase
Integration of a viral DNA ;copy into a host chromosome is called…
provirus
Virion maturation involves moving newly made virions to specific sites in the cell for…
- intracellular trafficking
- assembly
What is the most important part of virion assembly?
Placement of the viral genome inside the capsid
Virion is assembled while…
the viral genome is being synthesized
During virion assembly, the viral genome will be inserted into…
already formed capsids
What are the two ways new virions can be released from cells?
- Lysis (non-enveloped)
- Budding (envoloped)
Lysogenic infection is also known as…
latent infection
With a lysogenic infection, what happens to the viral genome?
Viral genome becomes incorporated into host cell’s DNA, remaining for a long period of time
Give three examples of lysogenic/latent infections
- HIV
- Hepatitis B and C
- HPV
Describe the number of virions over the course of an acute infection
Initial number of virions drops for a short eclipse period followed by a longer spike of virions being released from the host cell that peaks and declines
How long will an acute viral infection last?
A matter of days
Describe the number of virions over the course of a persistent infection
Gradual increase in virions followed by a spike
Describe the number of virions over the course of a latent infection
Sudden spike in virions with a later onset than acute infection
How long will a persistent infection last?
Months to years
How long might it take to see a spike in virions from a latent infection?
Months to years
What is antigenic shift?
Process of viral antigenic variation caused by the reassortment of genes
Shuffling of the viral genome in antigenic shift leads to…
major changes in viral proteins
How does the host immune system react to viral proteins changed by antigenic shift?
Host immune system does not recognize the changed proteins
What is antigenic drift?
Process of viral antigenic variation that results from mutations
Can cytotoxic T cells recognize epitopes from antigenic drift?
No
What is the process of viral antigenic variation caused by the reassortment of genes?
Antigenic shift
What is the process of viral antigenic variation that results from mutations?
Antigenic drift
What are three types of vaccines for viruses?
- Live attenuated
- Inactivated (killed)
- Sub-unit
What are the contents of live attenuated vaccines?
Intact viral particles that have been mutated and selected for poor infectivity
What type of vaccine is used for MMR (measles, mumps, rubella) and oral poliovirus (OPV)?
Live attenuated
What are the contents of inactivated vaccines?
“Dead” or non-infectious virus via chemical or physical treatment
What type of vaccine is used for poliovirus?
Inactivated
What are the contents of sub-unit vaccines?
Immunogenic parts of the virus via genetic engineering and recombinant DNA technology
What type of vaccine is used for Hepatitis B?
Sub-unit
What is a prion?
How do they relate to propagation of a disease?
A misfolded protein; the active component of the infectious agent
Propagation of a disease and its features depend on self-replication of prions