General Virology 2 -Viral Replication Flashcards
Definition of viral replication
The formation of virons (extracellular or intracellular infectious form of a virus) during the infection process in the target host cells
What are viral factories?
Areas within host cell where replication occurs, each family of viruses has different factories (includes location in cytoplasm and nucleus)
nucleus= viral factories
Basic viral replication cycle looks like?
Smaller viruses encode 2-3 proteins for structure and replication, larger viruses encode more proteins that do what?
Proteins that counteract host responses
Give some examples of how large viruses proteins counteract host responses
Produce proteins that stop:
-interpheron signalling
-PRRs (little proteins that recognize pathogens)
-host’s gene protein expressions which stops interferon stimulated genes
Can also mess with immune responses, MHC presentation, cell cycle modulation, apoptosis, and autophagy
All of the above help viruses invade cells
Give the 5 steps of basic viral infection and replication
1) Viral attachment (engagement of viral particle w receptoer) only the capsid attaches
2) Internalization through endocytosis
3) Uncoating- genome exits from nuclear capsid
4) genome replication (form mRNA)
5) Translation to form structural proteins (all viruses do translation some just have more steps for it to be able to happen) happens in the ribosomes
6) Assembly of proteins (ribosomes and Golgi)
7) Exit/ Egress
What period occurs between attachement and maturation? And What is is called?
Eclipse period (2-12 hours)
When uncoating and replication happens
What is the latent period?
Time between attachment to release
Includes uncoating/replication and maturation
What is tissue tropism?
The capacity of a virus to infect cells selectively in particular organs
For a host cell to be susceptible to a virus it must have?
Suitable surface receptors required for attachment and entry into cells
What is Permissivity?
cellular machinery must be able to support viral replication and release of new infectious particles
Viruses need what in order to infect and spread?
Susceptibility and Permissivity
The receptors viruses bind to is that their main function?
NO! receptors are not for viral infection, have a different purpose but viruses uses it
Describe the process of viruses and viral receptors interacting
-Initial contact with target cell and virus is by chance
-viral paricles then specifically attach to receptors on cell surface (example rabies attaches to CD155 )
Can different viruses bind to the same receptor?
Yes!
Can viruses bind to more than one receptor?
Yes!
ex) Both HIV and Rabies can bind to multiple
How do enveloped viruses enter host cells?
Following binding to the receptors there is direct membrane fusion (as envelope is a lipid bilayer), then endocytosis
Remember only the capsid enters!
The glycoproteins on the envelope are …
Similar to glycoproteins on cell membrane
What are the two ways naked viruses enter host cells
receptor mediated endocytosis (by making membrane bound vesicles)
Form pores in the cell membrane for entry (has a viral pore forming peptide accositated with the capsid so that only the genome enters)
Adenoviruses enter how?
naked receptor mediated endocytosis
Picornaviruses enter cells how?
forming holes in cell membranes
Corona viruses enter cells how?
enveloped therefore, direct fusion
Mimivirus is what type of virus and enters how?
Large enveloped virus and enter via phagocytosis
Which step in viral replication is used by all viruses?
Translation
dsDNA viruses replicate where? And what is their replication strategy?
Site: Nucleus
Strategy: uses host cell RNA polymerase 2 to make mRNA+
What is the exception of dsDNA viruses that uses a different strategy? And where do they replicate?
Pox virus, Asfa virus, Irido virus (they are large and carry their own viron transcriptase) and replicate in cytoplasm
Give some example of ds DNA viruses
Adeno
Hepadna
Herpes
Papilloma
Polyoma
ss DNA viruses replicate where? And what is their replication strategy?
Site: Nucleus
Strategy: uses host cell DNA polymerase (to make ds DNA intermediate) then uses host cell RNA polymerase 2 to make mRNA+
Give some examples of ssDNA viruses (2)
Anello
Circo
Parvo
ds RNA viruses replicate where? And what is their replication strategy?
Site: Cytoplasm
Strategy: uses viron RNA dependant RNA polymerase (that it carries so does not need host cell pol) to make mRNA+
Give some examples of dsRNA viruses
Reo
Birna
ssRNA(+) viruses replicate where? And what is their replication strategy?
Site: Cytoplasm
Strategy: Their viral genome act as mRNA
Give some examples of ssRNA(+) viruses (3)
Picona
Flavi
Calici
Astro
Corona
ssRNA(-) viruses replicate where? And what is their replication strategy?
Site: Cytoplasm
Strategy: uses viron RNA dependant RNA polymerase (that it carries so does not need host cell pol) to make mRNA+
Give some examples of ssRNA(-) viruses
Rabdo
Filo
Borna
Paramyxo
Orthomyxo
Bunya
What kind of virus is delta virus? How does it replicate?
It is a ssRNA(-) virus but uses host cell RNA Pol 2 to make mRNA+
Describe how retro viruses replicate
Site: Cytoplasm AND nucleus
Strategy: Virus is ssRNA + and carries reverse transcriptase, integrase and protease. The virus directly fuses with cell membrane it uncoats and the reverse transcriptase makes ssDNA form the viral ssRNA+. Reverse transcriptase then makes complementary DNA strand so now have dsDNA (this happens in cytoplasm) . Integrase then incorporates the dsDNA into the host DNA (in the nucleus). Therefore when cell is undergoing transcription it makes viral mRNA (moves to cytoplasm) and are translated into viral proteins. Viral proteins (including reverse transcriptase, integrase and protease) self assembly . They then bud off from cell membrane, they are immature and called a nascent viron. Protease then cleaves proteins, they are then mature and infective.
Give an example of retro viruses
EIA virus
HIV
Give details of herpes virus entry, replication and egress
Is a dsDNA envoloped virus
-Virus ligand binds with cell receptor and capsid and genome enter
-Viral DNA goes to nucleus
-uses host DNA polymerase to transcribe then translate alpha protein.
-Alpha protein is a regulatory protein so it then re-enters the nucleus and initiates the transcription and subsequent translation of beta regulatory protein
-beta regulatory protein then re-enters the nucleus and initiates the transcription and subsequent translation of gamma regulatory protein
-It renters the nucleus and initiates the transcription of viral structural proteins and capsid proteins.
-The capsid then buds through the NUCLEAR MEMBRANE becoming enveloped that contains glycol proteins.
-It is now called a Progeny virus and goes to ER then Golgi
-then exits the cell via budding= mature
HIGHLY REGULATED PROCESS
Describe entrance, replication and egress of flavivirus
Is a ssRNA+ virus (therefore genomic RNA is infectious)
-Virus enters by receptor mediated endocytosis
-Viral replication then happens in the cytoplasm
-SINGLE polyprotein is translated from genomic RNA and cleaved co/post-translationally
-buds from plasma membrane
How do enveloped viruses leave host cells?
By budding
Does budding lysis the host cell?
No, but weakens or kills it over several days
Examples of enveloped viruses?
Herpes and pox viruses( DS DNA)
Corona (+RNA)
Influenza (-RNA)
NO enveloped ssDNA
How to naked viruses leave host cells?
Lysis! They accumulate in nucleus or cytoplasm causing lysis
Example of naked viruses? (3)
reovirus (RNA)
Parvo (ss DNA)
Papilomma (dsDNA)
do all viruses bud from the cell membrane?
NO! (remember herpes buds from nuclear membrane), can also bud from endoplasmic reticulum, Golgi, apical and basal surface of cell membrane
Release from apical cell membrane surface is advantageous why? What viruses do this?
efficient transport as they exit into a lumen (typically coughed up)
Rabies, influenza, paramyxoviruses
viruses that exit from basal surface cause what? What viruses do this?
Causes lesions because is pushed up
alphavirus, vesicular stomatitis virus, lentivirus
