Microbio Week 9 - How Viruses Replicate and Change (Exam 3) Flashcards
Are viruses good targets for antivirals?
NO
What do viruses use for replication?
Host cellular products
Name the steps of replication
- Attachment
- Tropism
- Entry
How does a virus attach?
Bind to cellular receptors on host cell
If a cell does not have the viral receptor, the virus cannot do what?
Infect the cell
What helps determine what cells the virus can infect (aka the tropism of the virus)?
The viral receptor
T/F: There are other determinants of tropism other than receptors. For example, some viruses can enter certain cells, but if the cells are missing a cellular factor required for viral replication, the virus will not be able to replicate
True
What determines not only what cell type the virus infects but also the species of animal it can infect?
Tropism
What type of transmission is tropism important in?
Zoonotic
Entry at the cell membrane is mainly used for what type of viruses?
Enveloped
Some enveloped viruses can fuse the lipid bilayer of the virus with what?
The cell membrane
Both enveloped and naked viruses can be ___________
endocytosed
What helps the virus enter the cytoplasm from the endosome?
Lower pH of the endosome
Where does most DNA virus replication occur?
Nucleus
Where does DNA virus replication occur for poxvirus? (exception)
Cytoplasm
Where does DNA virus replication occur for HBV? (exception)
Nucleus + cytoplasm
What are the 3 DNA viruses that do NOT make their own viral DNA polymerase?
Papillomavirus
Polyomavirus
Parvovirus
What do Papillomavirus, Polyomavirus, and Parvovirus use to replicate their viral DNA?
Cellular DNA polymerase
What phase of the cell cycle must the cells be in for Papillomavirus, Polyomavirus, and Parvovirus to replicate their viral DNA?
S-phase
Papillomavirus and polyomavirus can cause cell-cycle ____________ by inhibiting pRb and making the cell go into cycle.
However, if the virus causes cell cycle dysregulation but does not kill the cell, there is a chance for the cell to become ______________
dysregulation; cancerous
Which virus (papilloma, polyoma, or parvo) cannot cause the cell to enter the S-phase and must infect cells already replicating?
Parvovirus
What do poxviruses have to make mRNA?
DNA-dependent RNA polymerase
What does HBV have?
Reverse transcriptase
mRNA is the same as what?
+ssRNA
When +ssRNA viruses enter the cell, what can they do right away?
Make protein
the first thing +ssRNA viruses do when they enter the cell is use the cellular machinery to translate their +ssRNA into a large polyprotein.
What is the exception?
Retroviruses
+ssRNA must cleave the large polyprotein they make into what individual viral __________. This means all +ssRNA viruses have what?
proteins; viral protease
T/F: All RNA viruses must make a viral RNA-dependent RNA polymerase
True!
What 2 things do all +ssRNA viruses have that are excellent targets for antiviral drugs?
Viral protease + polymerase
Retroviruses are +ssRNA viruses with how many copies of the same genetic material?
2
Which virus is diploid?
Retrovirus
Why are retroviruses unique?
Make a DNA copy of themselves using reverse transcriptase as part of their replication cycle
T/F: The reverse transcriptase used by retroviruses is carried into the cell; it is in the virion
True
Once retroviruses make a DNA copy of their genetic material, they integrate that copy into the host cell chromosome.
How long is that viral DNA copy in the cell?
For the life of the cell
Retroviruses use the cellular RNA polymerase to make viral ________ from the integrated viral DNA. This mRNA travels to the ___________, where it is made into _____________
mRNA; cytoplasm; protein
In HIV (a retrovirus), when does the viral protease cleave the viral proteins?
After budding of the virion
What helps mature viral particles from retroviruses?
Protease
What is the first thing -ssRNA viruses do when they enter the cell?
Make mRNA from their -ssRNA
How do -ssRNA viruses make mRNA from their -ssRNA?
Use a viral polymerase that goes into the cell with them in their virion
Do -ssRNA viruses need a protease?
NO - they make mRNA for each viral protein
Which virus is a “defective” virus that must co-infect a cell with HBV in order to replicate?
Hep D virus
What is this describing?
2 viruses of the same type infect the same cell. They might switch parts of their genome by recombination, which can result in several proteins being replaced at a time between the strains, resulting in a large change
Gene recombination
What is needed for gene reassortment?
Segmented genome
Which family of viruses have segmented genomes?
BOAR viruses
(bunya, orthomyxo, arena, reo)
What is it called when two strains of the same segmented virus infect the same cell?
Reassortment
What is this describing?
The resulting viruses have segments from both
infecting stains, resulting in a very different virus from the parental strains
Reassortment
What is responsible for the majority of influenza pandemics?
Reassortment
2 examples of antigenic shift (large changes)
Recombination
Reassortment
Example of antigenic drift (small changes)
Mutation
Different polymerases have different _________; they have different error rates and ability to correct mistakes
fidelity
Rank the following from lowest to highest mutation rate:
DNA viruses
RNA viruses
Higher eukaryotes
Prokaryotes
Higher eukaryotes < Prokaryotes <DNA
viruses< RNA viruses (highest mutation rate)
T/F: A base inserted by mistake will not be corrected by RNA viruses, leading to a higher mutation rate
True
Most RNA viruses cannot do what?
Proofread
T/F: It is possible in chronic infections, when antiviral therapy is started, a virus carrying a mutation resistant to the antiviral is already present. This can be true for HIV and HCV, which is why combination therapy is so necessary
True
If you have a chronic infection, which
allows the virus to replicate many times, you could have lots of different viruses in the body at any one time (HIV and HCV) or put another way, many _______________ of the virus
quasi-species
What helps viruses change rapidly with changing environmental conditions?
Making single nucleotide changes every 1-100 viruses produced
