| what does a virus consist of? | a virus particle is called a virion.
a virion is composed of its own genome, either DNA or RNA, which is packed in a protein coat called the capsid. sometimes a membrane called the envelope is present |
| what types of RNA can be present in a virion? | positive sense RNA (+)
negative sense RNA (-)
double stranded RNA (+/-)
ambisense RNA |
| what is the nucleocapsid? | the capsid and the genome of the virion together |
| how is a capsid synthesised? | individual proteins assemble to subunits
subunits form protomers
protomers form capsomeres
capsomeres form procapsid
procapsid forms the capsid when the genome is added |
| what are the three shapes of viruses? | helical: capsid has a central cavity with genome in the middle
icosahedral: made up of equilateral triangles fused in a spherical shape, fully enclosing the genome
complex: both helical and icosahedral e.g bacteriophages |
| what are the different steps of viral replication? | 1. recognition
2. attachment
3. penetration
4. uncoating
5. transcription
6. protein synthesis
7. assembly
8. lysis and release |
| what is the host range and tissue tropism of the virus? | host range: the spectrum of species which the virus can infect
tissue tropism: the spectrum of different cell types the virus can infect |
| how does the virion attach to the host cell? | with the capsid itself or with viral attachment proteins such as glycoproteins. |
| what are the different routes of viral transmission between humans? | - respiratory-aerosol route: breathing in droplets of someone's cough, sneeze
- fecal-oral route: ingesting particles of infected feces
- sexual transmission |
| what is the first response of the innate immune system to a virus? | viral RNA, DNA and some viral glycoproteins activate TLRs, this increases body temperature and causes fever, which can already limit replication or destabilize viruses |
| how can the interferons be classified? | interferon-alpha: type I interferon, produced by B cells, epithelial cells, monocytes, macrophages and DCs
interferon-beta: type I interferon, produced by fibroblast
interferon-gamma: type II interferon, produced by activated TH1 cells and NK cells, inhibits viral replication
interferon-lambda: type III interferon, produced at epithelial and endothelial barriers to promote viral infection and healing |
| how are interferons activated? | type I interferons: mostly by double stranded RNA
interferon-lambda: by NK cells |
| what reaction do interferons cause? | 1. interferons bind to receptors on neighboring cells
2. this induces the production of antiviral proteins, antiviral state activated
3. antiviral proteins are activated when bound to double stranded RNA
4. enzymes 2.5-oligoadenylate synthetase and protein kinase R are activated
5. causes inhibition of protein synthesis and mRNA degradation
6. viral replication is inhibited |
| how do NK cells kill? | 1. synapse is formed between NK cell and target cell
2. perforin and granzymes are released to disrupt the target cells
3. apoptosis is induced
interaction of the FasL receptor on the NK cells and Fas protein on the target cell also induces apoptosis |
