Viruses 1 - Structure Flashcards
Viruses are non-cellular - what does this mean?
No nucleus
No cytoplasm
No organelles
What are viruses?
Small parasite/particle/agents
Viruses are obligate intracellular parasites - what does this mean?
They cannot reproduce outside of the host
How do viruses produce proteins and nucleic acids needed to reproduce?
- They are inert outside of host
- So they utilise host cell processes to produce proteins and nucleic acid needed to reproduce
What does a virion (entire particle) consist of?
Nucleic acids and protein capsule.
What can be used for classification of viruses?
RNA or DNA with protein structure
What standard organelles do viruses lack?
Mitochondria
Chloroplasts
What is differential diagnosis?
Possible conditions that share the same symptoms - could have many diagnoses.
What are the different ways we can classify viruses?
1) Nature of genome
2) Presence of an envelope
3) Morphology
4) Genome configuration
5) Genome size
6) Virion size
What are examples of poxviridae?
1) Bovine papular stomatitis virus - not in UK
2) Orf in sheep and goats
What are examples of Herpesviridae?
1) Aujeszkys disease in pigs - eradicated from UK but could return
2) Bovine infectious rhinotracheitis (IBR) = common
What’s in the normal cat vaccine?
- Feline herpes virus
- Feline calicivirus
- Feline infectious enteritis
- Feline leukaemia virus
What are examples of Parvoviridae?
- Parvovirus in dogs
- Feline panleukopenia in cats
What are examples of paramyxoviridae?
- Rinderpest = ruminants
- Newcastle disease = major poultry disease (vaccination)
- Canine distemper in dogs (vaccination)
What’s an example of coronaviridae?
- Feline enteric coronavirus
- Feline infectious peritonitis (FIP) = fatal
What is the size of most viruses and what do we need to see them?
20-250 nm
Require electron microscope
What is the size of most bacteria and what do we require to see them?
5-10 um
Light microscope
What is the size of a human erythrocyte and what do we require to see it?
8 um
Light microscope
The genome contains either … or …
DNA or RNA
What viruses are double stranded?
DNA viruses
What viruses are single-stranded?
RNA viruses
DNA replication happens where?
In the nucleus
Where does RNA replication happen?
Mostly in the cytoplasm
Where are DNA genes found and what type of mutation?
All genes are found on a single molecule (mostly small point mutation)
Where are is RNA found and how does it allow for faster mutations?
Found on different molecules and segmented allows for faster mutations
Which has a higher mutation rate - DNA or RNA?
RNA
Are DNA viruses stable or unstable?
By process of elimination what are RNA viruses?
DNA viruses = stable
RNA viruses = unstable
Positive sense vs negative sense are to do with what?
They are to do with the ability to produce viral proteins directly or through intermediate stages
What is antigenic drift?
Where a virus is genetically diverse as a consequence of accumulating and tolerating point mutations
What is antigenic shift?
Where a virus (eg influenza) can reassort their segmented genomes to generate novel viruses with altered host range and virulence
Why can RNA be immediately translated by the host cell?
Positive sense viral RNA is similar to mRNA so can immediately be translated by the host cell
Positive sense means…
Segmented
Negative sense means…
Non-segmented
What components make up an enveloped virion?
matrix
membrane glycoprotein (peplomer)
capsid
lipid envelope
genetic material
What components make up a naked or non-enveloped virion?
Capsid
Genetic material
What is a capsid?
A protective layer surrounding the nucleic acid
Where is a capsid found?
In both enveloped and naked viruses
What is a capsid composed of?
Comprised of capsomeres - proteinaceous
The shape of the capsid is the characteristic of a virus - what 3 forms of symmetry?
Icosahedral
Complex
Helical
Describe a Icosahedral capsid
- Composed of capsomeres - subunits of capsid
- Icosohedron - polyhedron with 20 faces
- Polyhedron = three dimensional shape with flat polygonal faces - straight edges and sharp corners
- Very structural
- Campsomere - repeated protein subunit
efficient and requires less coding as repetitive
What symmetry does a icosahedral have and what may it look like?
- 5-3-2 symmetry
- May look spherical
An icosahedral capsid is very stable and non-enveloped which means …
It can survive months in the environment
What in a normal dog vaccine
- Parvovirus
- Distemper
- Leptospirosis
- Infectious hepatitis
- Kennel cough
Describe a helical capsid
Structural unit = single type of protein arranged around central axis - forms helical structure
Is a helical capsid enveloped or non-enveloped?
Enveloped
What does a helical capsid produce?
Produces rod-shaped or filamentous viruses
Describe a complex capsid?
- Neither icosahedral or helical
- Very large viruses
- Animal viruses - only poxviridae
What is an envelope?
A lipid coating surrounding the virion.
What does an envelop have for binding to receptor sites?
Glycoprotein spikes
How does an envelope affect a virus?
Affects how and where a virus replicates and therefore effects pathogenesis and host immune response
Name the components of a virus?
- Lipid membrane (from the host)
- Proteins spikes (glycoprotein)
What sugars are linked to an envelope?
- Haemaglutinin (HA)
- Neuraminidase (NA)
Name 4 enveloped viruses?
Rhabdoviridae (e.g. Rabies)
Orthomyxoviridae (e.g. Influenza)
Paramyxoviridae (e.g. Canine distemper)
Coronaviridae (e.g. Coronavirus)
Name 2 non-enveloped viruses?
Picornaviridae (e.g. FMD)
Parvoviridae (e.g.Parvovirus)
What are non-enveloped viruses?
- Surface = protein
- Stable in regard to: Temperature, pH, proteases, detergents, drying, released by lysis
- Resistant to detergents
What are enveloped virus?
- Surface = lipids, proteins, glycoproteins
- Labile in regard to:
- Acids, detergents, drying, heat. released by budding
- Easily destroys by detergents
So due to the structure of a non-enveloped virus what does this mean for its functions?
- Easily spread
- Can dry out and retain infectivity
- Can survive adverse events in the gut
many lyse cell to exit
So due to the structure of a enveloped virus what does this mean for its functions?
- Less easily spread - large droplets, secretions, infusions
- Less likely to survive in GIT
- Do not need to destroy cell to be released
What are structural proteins?
Capsid or envelope proteins
What do non-enveloped capsid proteins do?
Protect Genome
And deliver viral nucleic acid to cell to enable attachment
Enveloped glycoproteins are embedded in what layer?
Embedded in lipid layer
Why are glycoproteins encoded and what are they encoded by?
Glycoproteins are encoded by the virus for attachment
What is a non-structural protein?
A protein not involved in structure - often an enzyme.
What is a non-structural protein produced in?
- Produced in host cell by virus following infection
- Virus manipulating host to own advantage
Why are non-structural proteins useful?
Can be useful for identifying viruses
Helps differentiate infected from vaccinated animals
