Virus Replication Flashcards
What is a permissive cell?
A cell in which a virus is able to replicated
What is a non-permissive cell?
Cells in which a factor or factors needed for viral replication is not present or one detrimental to viral replication is present
What is the multiplicity of infection (MOI)?
Refers to number of virions that are added p/cell during infection
The eclipse period is after uncoating and before 1st appearance of what kind of virus particle?
Intracellular
The latent period is after uncoating and before 1st appearance of __________ new virus particle
Extracellular
What are the 4 components of the one-step virus curve growth?
- Adsorption
- Eclipse period
- Latent period
- Burst size
What is adsorption?
Virus attaches to and enters cells; titer of free virus in medium may actually decline
What is burst size?
Number of infectious virions released per average cell
What are the 6 steps in virus replication?
- Attachment
- Penetration
- Uncoating
- Synthesis of Viral components (Nucleic acid and protein)
- Assembly and maturation
- Release in large numbers
T/F: Virus attachment to receptor(s) on host cells is/are very specific, like lock-key
True
Attachment to host cell surface is mediated by what two interactions?
Interactions between virus and complimentary receptor on host cell surface
T/F: In some cases, attachment requires an additional cell surface molecule, or co-receptor
True
What are two ways non-enveloped/naked viruses penetrate and uncoat host cell?
- Receptor mediated endocytosis (common)
2. Pore mediated penetration
What are two ways enveloped viruses penetrate and uncoat host cell?
- Surface membrane fusion (pH independent fusion protein)
2. Receptor mediated endocytosis (pH dependent fusion protein)
With is another/uncommon mode of entry for viruses?
Antibody-mediated attachment and penetration
What is an example of receptor mediated endocytosis for non-enveloped viruses?
Clathrin-mediated endocytosis
For an enveloped virus, surface membrane fusion occurs directly on host cell surface and is facilitated by pH (independent or dependent?) fusion protein
Independent
Receptor mediated endocytosis for enveloped viruses, fusion protein requires (high or low?) pH to get activated and is thus pH (dependent or independent?).
Low pH
pH dependent
What happens during virus uncoating?
- Release of viral genome in host cell
2. Virion can no longer be detected
Once uncoating is done, virions have a loss of __________
infectivity
What two functions does the parent virus have?
- Multiple copies for new viruses
2. Viral proteins for capsid and successful replication
What is reverse transcriptase?
Used by retroviruses for conversion of viral RNA to cDNA during virus replication
T/F: During processing of primary RNA transcript (pre-mRNA), the viral mRNA must conform to requirements of host cell translation system
True
What are the 3 series of modifications, known as processing of primary RNA transcript (pre-mRNA)?
- Capping
- Addition of PolyA tail
- Splicing
After processing of primary RNA transcript (pre-mRNA), mRNA is translated in the _________
Cytoplasm
Capping is the addition of 7-methylguanosine to the ____ end of RNA
5’
Addition of poly-adenylated tail is at the ______ end of RNA
3’
RNA splicing is a process that removes __________ and joins ____________ in a primary transcript
- Introns
2. Extrons
What are two types of viral mRNA?
- Monocistronic
2. Polycistronic
Monocistronic viral mRNA encode how many polypeptides?
One
Polycistronic encode how many polypeptides?
Several
T/F: Assembly and maturation of virus genome and proteins into new virions follow any order
False, follow a specific order
Assembly and maturation may take place in what 3 cellular locations?
- Nucleus
- Cytoplasm
- Plasma/cell membrane (most enveloped viruses
How do naked virions release progeny virions?
Lysis of host cell
How do enveloped virions release progeny virions?
Budding
Why can’t naked virions exit host cell via budding?
Lack envelope
Viruses that acquire envelope while budding from ER, Golgi apparatus or nucleus membrane leave infected host cell by _______________
Exocytosis
What are two ways retroviruses replicate?
- Reverse transcriptase (RNA to DNA)
2. Integrase (integrate viral DNA into host genome)
What are the two ways viruses acquire lipid envelope?
- Host cell
2. Budding
What are 3 ways of cell-to-cell spread of viruses?
- Extracellular spread
- Intracellular spread
- Nuclear spread of virus genome
What 3 things result from intracellular spread of viruses?
- Rapid virus dissemination
- Evasion of immune system
- Persistent infections
T/F: An exon codes for amino acids and an intron does not code for amino acids
True
