Virus Lecture Sep 9 Flashcards
In what three ways are human viral pathogens classified?
- virion structure
- genome organization
- replication strategy
WHat is the infectious virus particle called?
virion
How do viruses produce disease? How do they NOT produce disease?
They produce disease by multiplying. THey do not cause disease by producing toxins.
Viral genomes are —loid, except for retroviruses which are —loid.
Viral genomes are haploid except for retroviruses whch are diploid.
What are the different possible genomic orgnizations?
dsDNA
ssDNA (+ or -)
dsRNA
ssRNA (+ or -)
they can be linear or circular (some linear RNA genomes are segmented)
Where are the capsomeres encoded?
In the viral genome
In general, what are the two potential capsid shapes?
helical (cylindrical) or icosahedral (cubic)
What are viral attachment proteins?
WHere are they located in naked viruses? In eveloped viruses?
The VAPs are proteins that interact with receptor on the target cell to facilitate penetration.
In naked viruses the VAPs are located on the capsid itself.
In enveloped viruses the VAPs are located on the envelope.
They just need to be on the outside of the cell.
What two roles do VAPs play in enveloped proteins?
VAPs help the virus adhere and penetrate cells.
Then when new viral particles are being assembled, VAPs are placed in the host cells cytoplasmic membrane and signal whhere the virions should bud out.
As they bud out they take the membrane with the VAPs with it to form the envelope
What’s special about retroviridae viruses?
They are the only ones that are diploid.
What’s special about orthomyxoviridae viruses?
They have segmented linear genomes
Will helical-capsid viruses always have an envelope or never have an envelope?
They always have an envelope
What three things does viral host range depend on?
- Can the virus enter the cell?
- Can the virus find/use the appropriate cellular machinery?
- Can the virus exit the cell?
What is the difference between a productive infection and a non-productive infection?
Viral infections of cels that yield new infectious viruses are called productive (lytic)
Non-productive viral infections occur when the viral genetic material persists in a cell (latent state) but no infectious virus is formed
What are the 6 phases of viral multiplication?
- attachment
- penetration
- uncoating
- virus component synthesis
- assembly
- release
What are cytopathic effects?
Cytopathic effects are morphological changes to the host cell that result from the synthesis of viral proteins and viral effects on host macromolecular synthesis
Examples are cell rounding, cell fusion, etc.
Some herpes viruses have the ability to synthesize a protein in their envelope which allows the enveop to fuse with the host cell. Because the protein stays in the host cell membrane, infected cells will adhere to uninfected cells forming multinucleated giant cells
How does a naked virus release it’s nucleic acid into the cytoplasm of the cell?
How do enveloped viruses release their nucleic acid into the cytoplasm? THere are two ways.
When the virus penetrates the cell it’s placed into a lysosome, where the capsid is degraded, releasing the nucleic acid.
An enveloped virus can do one of two things. It’s membrane to can fuse with the cytoplasmic membrane, dumping the nucleic acid out into the cytoplasms.
Or…It the virus can penetrate without losing its envelope, in which case it’s brought into a lysosome. The viral envelope then fuses with the lysosomal membrane and the nucleocapsid is ejected.
Where do DNA viruses replicate?
Where do RNA viruses replicate?
What are the two big exceptions to this rule?
All DNA viruses replicate in the nucleus because it needs the DNA polymerase enzymes that are only located in the nucleus.
THe vast majority of RNA viruses replicate in the cytoplasm.
The two big exceptions are AIDs and Influenza virus, both of which replicate in the nucleus.
What is a viroporin?
A small hydrophobic virus-encoded protein that oligomerize at host cell membrane where they are involved in enveloped virus budding and non-enveloped virus cellular lysis
THey have several cytopathogenic effects on the cell including the formation of hydrophilic pores and alterations of calcium and hydrogen gradients
How do naked proteins get out of a cell?
How do enveloped viruses get out of a cell?
Naked viruses lyse the cell
Enveloped viruses bud out
If enveloped viruses can leave host cells through budding, how does the host cell die because of the infection?
BUdding does not lyse the cell.
The cell is attacked by the immune response because budding requires that the VAPs be placed on the host cell’s cytosolic membrane.
The immune response then recognizes the cell as forieng and mounts a response against it.
Describe a one step growth cycle for a virus.
What is the eclipse period?
What is the latent period?
FIrst there is an initial dip when the virions per cell reaches almost 0 – this occurs because all the first viruses get absorbed into the cell.
After a while, you get infectious virus formed. Up to the time point when virions begen to form WITHIN the cells is the eclipse period.
As time passes, these intracellular virions mature and leave the cell. The time up to this point is the latent period.
When the curve reaches its peak, that is the yield or burst size. The total number of virions produced.
Will a cell that is actively replicating host a virus with a shorter or longer eclipse period?
Shorter. The cell is already replicating and the virus will therefore multiple much faster.
Describe the one step growth cycle for mRNA, DNA, early protein, and late protein within a host cell.
- THe first to form is the mRNA
- Soon after the mRNA beings to icnrease, a series of early viral proteins are translated. These early proteins are involved in the replication of nucleic acid
- About 6 hours after adsorption, DNA begins to increase
- Shorterly after this, early protein synthesis subsides and late proteins are synthesized. Late proteins are the structural proteins of the virus such as the envelope proteins or the nucleocapsid proteins.
Are all negative sense RNA viruses enveloped or naked?
enveloped
Why must RNA viruses produce their own replicase/transcriptase?
Because they replicate in the cytoplasm and the host cell doesn’t have cytopasmic RNA polymerase
What two families of RNA viruses do NOT replciate in the cytoplasm?
Orthomyxoviruses (i.e. influenza)
and retroviruses (HIV)
All ss RNA viruses (except retroviruses) repliecate via a ———- ——— intermediate.
All ssRNA viruses except retroviruses replicate via a ds RNA intermediate
Describe the genome organization of replication strategy of hepadnaviruses.
WHat is the classic example of a hepadnavirus?
Why do HIV medications work on hepadnaviruses?
Their genome is interesting because it is partially double stranded DNA.
They replicate their DNA in the nucleus via a RNA intermediate.
This involves an RNA-dependent DNA polymerase–reverse transcriptase
They can transform cells–linked to liver carcinoma
- The partial dsDNA goes into the nucleus
- Covalently closed circular DNA is made
- From the dsDNA, pre-genome RNA is synthesized–this is a full legnth RNA copy of the DNA
- THe RNA leaves the nucleus and enters the cytoplasm
- In the cytoplasm more copies of the RNA are made plus individual messages (for the nucleocapsid proteins)
- As the RNA move sto the surface, it is acted on by reverse transcriptase to make dsDNA.
- The RNA is degraded as it is read
- THe core particle with viral DNA escapes the cell
Hepatitis B is the classic example.
HIV retrovirals that target reverse transcriptase will often be given for this as well.
