Lec 2 - Virus rep cycle Flashcards
Where do RNA vs DNA viruses replicate?
RNA viruses replicate in the cytoplasm
DNA viruses replicate in the nucleus
What are the 6 steps of the viral replication cycle?
- Attachment to host receptors/coreceptors
- Penetration and uncoating to release genome into cell
- Synthesis of early non-structural proteins
- Synthesis of late structural proteins
- Assembly into virion
- Release of virion from cell
What are the functions of early non-structural proteins?
- Inhibit host cell protein synthesis
- Regulate viral gene expression
- Synthesise viral proteins for replication
What is a virus’ tropism?
The specific susceptible cells a virus can infect that support viral replication
What is a virus’ host range?
The range of species a virus can infect
What are the requirements for a successful viral infection?
- Dose = enough virus
- Access to susceptible and permissive cells
- Absent/weakened immune system
Compare the terms permissive, susceptible and resistant.
Permissive = may/not have receptor and supports viral replication
Susceptible = has receptor and may/not support viral replication
Resistant = no receptor and may/not support viral replication
What is cytopathic effect and what are 3 types?
Physical cell damage
1. Syncytium = large multinucleate cells
2. Inclusion bodies = sites of viral replication in cytoplasm or nucleus
3. Transformation = malignant development
What influence do coreceptors have on infection?
Influence the viral load and severity of disease
What are the 8 steps in influenza’s replication cycle?
- HA binds sialic acid on epithelial cell
- Endocytosis
- Uncoating = (-) ssRNA and vRNP to nucleus
- (-) ssRNA -> (+) ssRNA = dstranded template -> copy (-) strand -> mRNA
- mRNA to cytoplasm for translation
- Viral proteins to nucleus for assembly
- vRNPs assemble with other components at cell membrane
- Viral enzyme degrades cell membrane for release
How is a viral envelope made?
Viral envelope proteins glycosylated by cell’s glycosylation pathway and stick out of cell membrane until assembly. That part of the lipid bilayer becomes the envelope.
What are VRCs and how are they formed?
Viral replication complexes are sites of replication made from modified cytoskeleton, ER and Golgi body components
How do viruses spread from cells?
- Extracellular = release of virions from host cell
- Non-extracellular = sideways movement to adjacent cells without contacting extracellular environment
What is the MOI and what sort of assay is used to find it?
Multiplicity of infection refers to the number of virus particles added per cell and is found using a plaque assay
eg 10^7 virus to 10^6 cells has MOI = 10
eg 10^6 virus to 10^7 cells has MOI = 1
How are viruses that don’t form plaques quantified?
End point assay to determine the presence/lack of CPE. Highest dilution/smallest amount of virus with CPE = end point
