POS - Virology Replicatio Flashcards
How do viruses attach to cell surfaces?
Proteins/glycoproteins on the virus cell surface bind to receptors.
What is tropism?
Virus-receptor interaction determines specificity of viruses for cells and tissues
How does a virus attach to the cell?
Via multiple receptors or co-receptors with spike cleaved by enzymes preparing it for entry.
How does a virus enter the cell?
Via endocytosis, where the virus is released from an endosome by a pH change, and the viral envelope fuses with the endosomal membrane.
Via fusing directly
What is uncoating?
The release of viral nucleic acid from a viral capsid.
- Some capsids only partially disintegrate
- Some are still in a nucleoprotein complex
What is the classic viral replication cycle?
- Viral entry
- Replication
- Transcription and translation
- Assembly
- Egress
What are the 4 things viruses must be able to do?
Replicate the genome
Produce viral protein
Assemble new viral particles
Avoid the immune system
How is mRNA synthesised from DNA viruses?
mRNA is transcribed in the nucleus using cellular RNA polymerase.
mRNA is transported to ribosomes for translation
How is mRNA synthesised from RNA viruses?
Viruses need to use their own enzymes to make messenger RNA (RdRp)
RNA viruses remain in cytoplasm for replication and must avoid degradation
What is the difference between late and early proteins that are translated?
Early proteins - non-structural proteins (regulate viral transcription and replication)
Late proteins - structural proteins (capsid and envelope glycoproteins)
Where does genome replication occur?
DNA viruses - in nucleus
RNA virus - in cytoplasm
What are the exceptions to where genome replication occurs?
Pox viruses - viral factories in the cytoplasm
Influenza - replicates in the nucleus
How are genomes packaged into new particles?
Requires packaging signals to concentrate the viral components and is v complex
What are the three ways a virus can be released?
- Budding from plasma membrane
- Exocytosis
- Lysis of cell
Why grow viruses in the lab?
Research
Vaccine production
Virus as a tool
Diagnostics
What happens when you use chicken eggs to culture viruses?
Use 10 day old eggs - fertilised and requires sterile inoculaiton
Use different spaces depending on the virus: chorioallantoic, aminotic, yolk sac and allantoic
What are the advantages/disadvantages to culturing cells in vitro?
Easy to handle and easy to scale up, easy to obtain as well
How are cell cultures maintained?
Grow and cover the whole flask, treated with trypsin to detach from a plastic and then are passaged to a new flask.
What are primary cell cultures?
From a tissue sample, can survive for 10-15 days before differentation occurs preventing further cell division
What are continuous cell lines?
Immortalised cells that continue to grow and are derived from tumours.
Often lose receptors and have major abnormalities
What are organoids?
3D cell cultures derived from stem cells and can be used to model donors/cell growth etc
What are cytopathic effects?
Visible changes to cells following viral infections
e.g. the cells round up and detach or holes appear
What are syncytia formation?
Cells fuse to create large cells with several nuclei
What are inclusion bodies?
A mass of viral proteins within the cell
What are non-cytopathogenic viruses?
Nor all cells produce a cytopathogenic effect, need staining or qPCR to detect.
What are infectivity assays?
Used to quantify the number of infectious virus particles.
What is plaque assays?
A type of infectivity assay. Its done by 10 fold serial dilutions of virus samples and the virions infect cells giving rise to plaques.
Counting plaques - calculate virus titre
