L13 - Intro To Viruses Flashcards
What is the definition of a virus and what are its properties
Nucleoprotein complex which infects cells and uses the cells metabolic processes to replicate. Smallest known infective agent. Metabolically inner - must enter host to replicate.
Describe the viral morphology
- size
- structural components
- genetic content
10-400nm
Nucleocapsid
Envelope +/- (nucleic acid of virus is found in its protein capsid)
DNA/RNA, ss or ds
Linear or circular
Segmented (HIV)
What is the function of viral capsid
Protects nucleic acid and aids transfer between hosts
What is the structure and arrangement of capsid
Protein coat with capsomere arrangement:
- polyhedral, helical, complex
What is the subunit for capsid
Capsomeres
What is the diff between naked vs enveloped viruses?
Some capsid are naked (just the protein with crystal lattice structure) some have additional layer outside capsid made of lipid. Acts as glycoproteins to bind to receptors for DNA entry
Describe the viral envelope in terms of its location, source, components and examples
Location - surrounds capsid
Source - host plasma membrane, nuclear membrane, ER
Components - phospholipids, proteins, glycoprotein spikes
Examples - influenza, rabies, herpes, HIV
What’s the function of envelope glycoprotein spikes
Enables virus to interact with target cells and bind to receptors nd pass across membrane
What kind of virus does not affect human
Helical capsid non envelope
Describe the viral nucleic acid
- shape
- number of genomic segments
- strands
DNA or RNA
Circular or linear
One or more segments
Single stranded or double stranded
Outline the 4 types of strands
Single stranded RNA +ve sense (mRNA)
Single stranded RNA -ve sense (non-coding)
Double stranded DNA
Double stranded RNA
Describe the structure of adenovirus
Non-enveloped with icosahedral capsid, linear ds DNA
Spikes important for binding
Describe the structure of of herpesviridae
Enveloped, icosahrdral capsid, in between the 2 envelopes they have another element for infecting cells
Describe the structure of influenza virus
Less structured spike, helical nucleocapsid, enveloped
Describe the structure of Ebola virus
Helical nucleocapsid, enveloped
Describe the structure of pox virus
Linear ds DNA, enveloped, complex
What are the levels of virus classification
Nucleic acid DNA or RNA
If DNA : envelope yes or no
If yes: polyhedral (icosahedral) and helical cylindrical
Virus classification naming system
Suffix -> genera -> subtypes
What is the Baltimore classification?
All virus must direct the synthesis of mRNA to proteins. It describe the relationship between viral genome and mRNA (start point of synthesis is diff for virus)
- RNA virus is slightly diff
- → +ve sense can act as mRNA (goes thru intermediate to amplify)
- -ve (influenza) can act as mRNA when entering the cell but cant be copied so it is turned into +ve sense RNA to be translated
- ssDNA (parovirus) → dsDNA → gets integrated into genome as cellular genome
- all depends on starting point but all has to go through being mRNA as an intermediate
How are viruses grown?
In tissue culture, fibroblast continuously growing in cell line indefinitely or in fertilised chicken eggs (diff parts of the egg grows diff virus)
How is the plaque assay conducted (virus quantification
- 10 fold serial dilutions are titrated in duplicate
- plaques on the dilution is counted
- title is calculated
- plaque count x 1/dilution = PFU
Virus quantification-cpe
Cytopathic effect - use tissue culture infection to see which dilution of virus gives us critical signs of infection more than 50%
