Virology - Introduction Flashcards
Outline the basic properties of all viruses.
- Either RNA or DNA genome, either ss or ds, and either linear or circular
- Metabolically inert: only replicate after infection of a host and parasitise the host cellular machinery
- ‘Obligate intracellular parasites’
- Can have an enveloped or naked viral partical (virion)
- They are extremely small (~20-400 nm), requires electron microscopy to view
- Has symmetry, e.g. icosahedral, helical, or complex
Outline the strucure of an enveloped virus.
- Structural proteins: the proteins which make up the viral particle
- Non-structural (NS) proteins: enzymes, not incorporated into the virion
- Capsid: protein coat of a virus
- Capsomeres: the structural unit of the capsid
- Nucleocapsid: complex ot the protective protein capsid and the viral nucleic acid
- Virion/viral particle: the whole virus containing the nucleocapsid with its outer envelope (if present)
What is the differece between enveloped and naked viruses?
Naked viruses do not contain an envlope and tend to be more resistant to the environment, whereas enveloped viruses tend to be more susceptible to the environment and are transmitted in a different way to naked viruses.
What different morphologies of viruses are there? [5]
- Polyhedral (e.g. icosahedral)
- Helical
- Spherical
- FIlamentous
- Complex
What is this virus?
Ebola virus
Filamentous, ‘needle’
What is this virus?
Rabies virus
Complex, cylindrical, ‘bullet’
What is this virus?
Poliovirus
Complex, round
What is this virus?
Herpes virus
Icosahedral, enveloped, ‘fried eggs’
What is this virus?
Coronavirus
‘Spiked potato’
What is this virus?
Lassa virus
Round, complex, enveloped
APURAR
Overview the stages of infection. [6]
This is the general cycle, each individual virus has variations on this.
- Attachment: binds to specific receptor (ligand), usually a glycoprotein, e.g. gp120 binds CD4 in HIV, H and N receptors in influenza
- Penetration: endocytosis
- Uncoating: change in pH sheds capsid and releases genome
- Replication: viral replication of viral proteins
- Assembly: form mature virions
- Release: budding (influenze, HIV) or cytolysis
Outline the routes of viral transmission.
Most common:
- Inhaled droplets, e.g. rhinovirus
- Food or water, e.g. hepatitis A
- Direct transfer, e.g. HIV
- Bites of vector arthropods, e.g. yellow fever
There is specificity between virus and host through membrane interactions. Give some examples.
Outline the ways in which genomic RNA of RNA viruses can be transcribed into messenger RNA before translation into proteins.
Only +ve sense RNA can be translated into protein..
- -ve sense strand transcribed by viral RNA polymerase → +ve sense RNA.
- +ve sense strand is used directly.
- Retrovirus +ve sense RNA strand is transcribed into dsDNA by reverse transcriptase into -ve sense DNA. This is then transcribed into +ve sense RNA.
