Virus replication, structure, and classification (complete) Flashcards Preview

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how do viruses replicate

by assembly of subunits in infected cells


What are the steps for viral replication

1. attachement
2. penetration
3. uncoating
4. early transcription
5. early translation
6. replication
7. late transcription
8. late translation
9. assembly
10. release


What are the two ways that viruses can kill

causing an overactive immune system (angry macrophages)
inhibiting the immune system


what is the primary example of a virus that kills by causing an over active immune system



what is the primary example of a virus that kills bu inactivating the immune system

Ebloa (also HIV)


What is the main difference between positive and negative RNA virus replication

a positive strand is just like mRNA so it is immediately translated, negative strand mRNA has have a complementary strand made, then have that one translated


although positive and negative RNA virus replication is different, what is one important similarity

they both create double stranded RNA


why is double stranded RNA so important

it is the signal that induces the synthesis of interferon


can viruses resist interferon action



what is a retrovirus

an RNA virus that goes from RNA to double stranded DNA.


what is needed by a retrovirus, and can be the target of antiviral drugs



What is the main target of antibodies against viruses

antibodies against particles on the viral envelope, this prevents them from binding to the cell


What are the different outcomes of a viral infection for the cell

1. Abortive infection
2. Latent infection (can become a productive infection)
3. productive infection (can lead to cell death or a persistent infection)
4. apoptosis


What are the four immune mechanisms that fight viruses and what do they cause

1. interferon - blocks infection, kills infected cells
2. NK cells - kill infected cells
3. B cells/antibody - neutralizes viruses, enhance phagocytosis
4. Cytotoxic T-cells - kills infected cells


What are the TLRs that are important to antiviral activity

TLR 3, 7, 8, and 9


What does TLR3 recognize and result in

TLR 3 recognizes DsRNA and produces IFN-beta


what do TLR 7, and 8 recognize and result in

they recognize viral ssRNAand produce IFN-1 alpha


What does TLR 9 recognize and result in

it recognizes unmethylated CpG, and results in IFN-alpha


what type of cell produces the most IFN-alpha

plasmacytoid dendritic cells


what is the sequence of events from TLR recognition to IFN production

1. TLR recognition
2. signal pathway
3. transcription factors
4. Interferon production
5. Release of interferon
6. protection of non-infected cells


What is type 1 interferon

IFN alpha and beta
produced by immune cells and infected cells


what is type 2 interferon

antiviral and defense against intracellular bacteria and parasites
produced by immune cells only


What are the three ways in which interferons work

1. they inhibit all translation (type 2 IFN only does this)
2. they degrade mRNA and rRNA
3. they inhibit transcription, and viral assembly
(type 1 IFN does all three)


What does STAT do?

it causes IFN to be produced


how can viruses evade antiviral defenses

- Influenza NS1 binds to dsRNA
- Ebola prevents dsRNA from inducing IFN release
- Ebola inhibits RNA silencing
- adenovirus blocks STAT1 from functioning
- Vaccinia prevents IFN from attaching


What are the two ways that a virus can initiate apoptosis

extrinsic (death by instruction)
intrinsic (death by stress)


how is apoptosis carried out

activation of caspases, which basically chew everything in the cell up, then they are and ingested by phagocytes


is apoptosis good or bad for the virus inside the cell

it can be both. Some viruses initiate apoptosis, others prevent it so the cell will stay live and produce more virus


What is a latent viral infection

the viral genome is present, but there are no infectious viral particles


What is lysogeny

when a viral genome integrates into the host genome