Lecture 1: General Virology 2 Flashcards
Define viral replication
Viral replication: formation of virions in host (extracellular or intracellular form)
What does viral replication lead to
- Lead to productive replication
o Can switch between non productive stage (herpes latency)
o Spread in host (via lymphatics or blood) > release (mucosal surface/blood)> transmit
How to detect viral replication?
immunostaining or PCR (genome detect) or electron microscopy (whole virus visualize)
What is the significance for a virus having a larger genome size
- Only a few structural proteins are actual required
- Circovirus: Circular genome with 2 open reading frames (only 2 proteins made)
- Larger DNA viruses can code for many more (more non-structural proteins)
o Extra proteins used to downregulate immune system/cell cycle (regulate MHC1/PRRs/apoptosis pathways…)
What are the 8 steps of viral replication
Steps of Viral Replication
1. Virus attach to receptor
2. Nuclear capsid (genome + capsid) endocytosed (not envelope)
3. Penetrate endosome in cytosol
4. Migrate to relevant part of cell (ex. DNA virus go to nucleus)
5. DNA replication
6. Protein production
7. Assemble proteins + add genome
8. Release new virions
Define the eclipse period in viral replication
- Eclipse period: time after virus enters cell until new viral proteins are maturing
Define the latent period in viral replication
- Latent period: time from viral entry until release (uncoat +maturation)
Describe tissue tropism
Tissue tropism: ability of a virus to infect a particular organ
* Susceptibility: cells have specific receptor
* Permissivity: cell machinery can support viral genome
How do viral particles identify cellss to enter
Viral Receptors
Attach to membrane surface molecules
* Different viruses can bind same receptor or different ones – some have multiple
How to envelope viruses enter cells
- Bind receptor
- Fuse envelope bilary with cell membrane
- Internalize Capsid and genome via endocytosis
- Genome break out of capsid – uncoating
How to naked viruses enter cells (2 ways)
Receptor mediated endocytosis
1. Bind cell receptor
2. Entire virus endocytosed
3. Genome breaks out – uncoat
Pore-forming: picornaviruses
1. Bind receptor
2. Release pore forming peptide (on capsid) – penetrate cell membrane
3. Only genome injected into host cell
What step of protein production is used by all viruses
translation
What enzyme is used in the nucleus to convert DNA to mRNA
DNA dependent RNA polymerase
Poxvirrus carries its own
What types of viruses replicate in the cytoplasm, nucleus, or both?
- RNA virus: cytoplasm – because ssRNA(-) have own RNA dep RNA pol
- DNA virus: nucleus (except Poxvirus) – use host pol
- Hepadnavirus + retrovirus: both cytoplasm (reverse transcription) and nucleus (transcription)
Describe the steps of DNA virus replication? Specifically, herpesvirus
Herpes virus transcription
* Regulated transcription
1. Enter cell and go to nucleus
2. Produce many types of mRNA
o A – Block immune response and stimulate B production
o B – stimulate replication of genome and y production
o Y – stimulate structural protein mRNA production (capsid)
3. Package genome and protein and glycoproteins
4. Pinch off in cell membrane to create envelope
Describe the steps of RNA virus replication
RNA virus replication (flavivirus)
1. Enter cell
2. + sense RNA translated into poly protein
3. Poly protein is modifies via post translational cleavage
Describe the steps of Retroviral virus replication
Retrovirus replication (EIA virus)
1. Enter cell (carrries reverse transcriptase and integrase) via receptor
2. Uncoat
3. Viral RNA > ssDNA via viral reverse transcriptase
4. SsDNA > dsDNA > go to nucleus and integrate into host genome
5. Create viral RNA
6. Package to form nascent virion (not mature) > exit
o Nascent virion still has Gag and Pol glycoproteins – not infectious
7. Cleave glycoproteins extracellularly = mature
What makes retroviruses unique
they incorporate their genome into the host genome
meaning it is LIFELONG infection
Compare exit strategies of enveloped and non-enveloped viruses + examples of enveloped
Enveloped
* Only infectious if it has its envelope
* Via budding from various cell surfaces
* Ex.
o Mucosal surface: Influenza/rabies/paramyxovirus
o Basal cell surface: alphavirus/vesicular stomatitis virus/lentivirus
o ER/golgi: coronavirus/flavivirus/hepadnavirus
o Nucleus: herpes
Non-Enveloped
* Via cell lysis
Viruses cannot replicate in
- plants
- birds
-mammals
-bacteria
-water
water
Which cellular functions are used by all viruses?
A Energy production
B Carbohydrate synthesis
C Transport
D Lipid synthesis
E Nucleic acid synthesis
E Nucleic acid synthesis
An essential component of all virus particles is
A Minerals
B Carbohydrates
C Vitamins
D Proteins
E RNA
D Proteins
Presence of envelopes in some viruses
A Make them resistant to Natural killer cell attack
B Make them susceptible to Natural killer cell attack
C Make them resistant to cytotoxic cell attack
D Make them susceptible to cytotoxic cell attack
E Make them susceptible to chemical detergents
E Make them susceptible to chemical detergents
Some naked viruses deliver the viral genome across host cell membrane by
A Fusion of host cell membrane and viral envelop
B Attaching to a transport protein
C Phagocytosis
D A pore that is formed by protein components of the
viral capsid
E None of the above methods
D A pore that is formed by protein components of the
viral capsid
A unique feature of replication of retroviruses is
A Viral entry via a pore made in the cell membrane
B Egress of progeny viruses by host cell lysis
C Reverse transcription
D Use of cellular machinery for energy metabolism
E Viral protein synthesis in ribosomes
C Reverse transcription
A unique feature of replication of herpesviruses is
A Viral entry via a pore made in the cell membrane
B Egress of progeny viruses by host cell lysis
C Reverse transcription
D Viral replication in viroplasm
E Highly regulated viral replication in host cell nucleus
E Highly regulated viral replication in host cell nucleus
Poxvirus replication when compared to that of other
DNA viruses is unique due to
A Viral entry via a pore made in the cell membrane
B Use of host cell polymerases for DNA replication
C Reverse transcription step during viral replication
D Viral replication in cytoplasm
E None of the above
D Viral replication in cytoplasm
