Microbiology 4 - Viral properties Flashcards
What is a virus?
Infectious OBLIGATE intracellular PARASITES
Define the nature of viruses.
- Small size
- Dependence on a host
- Structural and genetic diversity
What are the dufferent morphologies of viruses?
- May have a symmetrical protein capsid and no envelope
- May be enveloped using the lipid membrane from a host (pleiomorphic/typical shape)
- May have both a capsid and an envelope
- Bacteriophages are the ones that look like spaceships
What is the central dogma for viral replication?
DNA -> RNA -> Protein
- Makes negative sense RNA (complmentary to the mRNA)
Why do viruses have a high mutation rate?
They use their own polymerases which have no proof reading capacity.
Why are RNA viral genomes limited in size?
RNA is more unstable than DNA
How does viral DNA/RNA appear?
- It can be segmented - similar to human chromosomes, which allows a form of recombination called re-assortment to occur.
- Can have viral sex
Describe the generic virus replication cycle.
- The protein coat binds to viral receptors on the cells (which have other functions)
- When inside, the virus falls apart and the genome is replicated
- Early regulatory proteins are synthesised
- Then late structural proteins
- There is then assembly of the late proteins with the viral genome
How do retroviruses work?
They integrate their DNA with the host DNA.
What is the cytopathic effect?
The virus lysing the cell - due to shut down of host protein synthesis or accumulation of proteins.
What are viral plaques?
A visible structure formed within a cell culture, where viruses replicate and spread to generate regions of cell destruction.
What are syncytia?
Multinucleated giant cells that form when viral proteins cause fusion of cells.
How is immunostaining of viral cells performed?
Antibodies are generated in the lab that bind to viruses and indicate the infected cells
Describe the growth phases of a virus.
1) Infection - an eclipse phase occurs where concentration of viruses outside the cells is low as the viruses all enter the cells
2) Logarithmic phase where the cells rapidly grow
3) Cell death - no cells are left so the graph will plateau
What are the methods of viral diagnosis?
- Detecting the viral genome using PCR
- Detect viral antigen using IFA (immunofluorescence assay/ELISA)
- Detecting virus particels (EM)
- Detecting the cytopathic affect in cultured cells (isolation)
- Detecting antibodies to virus (serology)
What does the method of viral diagnosis used depend on?
- Source of the specimen
- Purpose of test (therapy or surveillance)
- Who will use it and where
- What stage is the disease (active replication or antibody response)
How are viruses attenuated?
- Cells are grown in the lab and as a result they acquire mutations that adapt them to a new host
- This means that are no longer functioning in a human
- Used to make vaccines
How do norovirus cultures move to the target cells?
Enteric bacteria promote norovirus infection of B cells, which may allow the virus to cross the intestinal epithelium
How are viruses manipulated?
- Viral genomes can be synthesised and introduced into permissive cells to direct synthesis of their new component - made de novo
- Allows reverse genetics (create viruses with engineered mutations)
What are viruses named after?
- The disease
- The person who discovered it
- The place it was discovered
- The part of the body affected
- The way it was spread
What is the size range of viruses?
1-10 nm
