Viral properties Flashcards
What is the definition of a virus?
infectious obligate intracellular parasites (needs to host to complete life cycle)
What is the average size of virus?
100nm
Characteristic of an non-enveloped virus:
- Have protein capsid
- More symmetrical
Characteristics of enveloped virus:
- Proteins around genome
- Lipid envelope around, derived form host membrane
- Premorphic (have different shapes) e.g Ebola
How are viruses classified?
- Nature of genome: DNA/RNA, single stranded/double stranded
- RNA viruses carry RNA as either positive strand: can be directly translated
- Negative strand is antisense
What are the consequences of viral genome type for RNA and DNA viruses?
- RNA and retroviruses
- Use own polymerase to replicated which are pretty error prone and lack proofreading capacity so high mutation rate and faster evolution
- Limited in size because RNA instability
- Often use complicated coding strategies to encode more proteins than expected from small genome
- Proteins may be regulatory or structural
- DNA viruses:
- bigger because DNA more stable so space for accessory genes
- Segments allow for recombination
- Allows opportunity to pick up new genes and evolve
How do viruses replicate?
- Proteins used to attach to cell surface
- Engulfed and taken in as endosome
- Fuses and releases its genome
- Genome enters nucleus, replicates and directs protein synthesis
- Come together to form new virus
What receptors does HIV interact with?
CD4, CCR5/CXCR4
How are viruses studied in laboratory?
Cytopathic effect: death of cell as a result of being infected by virus
How is a plaque assay produced?
- Take sample from patient that contains virus
- Make serial 10 fold dilution
- Take known volume of dilution and put into susceptible cells
- Plaques on susceptible cells show how many viruses in dilution
What is the use of plaque assays?
If you count plaques can measure how many viruses in sample
What are syncytia?
Big bundle of cells stuck together by becoming 1 big cell with many nuclei
What viruses form syncytia?
Surface proteins that fuse at neutral pH
What are the 5 in which viral genomes detected?
- Detect viral genome
- e.g PCR
- Use primers unique to virus
- Detecting viral antigen
- indirect fluorescent antibody (IFA)
- Detecting antibody to virus (immunostain)
- Serology in blood
- Use flu
- Detecting viral particles
- Detecting virus cytopathic effect in cultured cells
- Virus isolation
What is the difference between primary and continuous cell lines
Primary cell cultures:may include several different cell types and may retain aspects of the original tissue.
Continuous cell lines:are monocultures propagated indefinitely due to their transformation.
How are viruses altered?
Reverse genetics techniques: engineering cDNA that represents the sequence of the virus genome, introducing it into cells and recovering an altered virus.
Growing the virus under different conditions,
induce changes in the genome and studying their effects.
