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 cell
How do viruses produce proteins and nucleic acid to reproduce?
- they are inert outside of host
- so utilise host cell processes to produce proteins and nucleic acid 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 genome 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?
- nature of genome
- presence of an envelope
- morphology
- genenome configuration
- genome size
- virion size
What are examples of poxviridae?
- Bovine papular stomatitis virus - not in UK
- orf in sheep and goats
What are examples of Herpesviridae?
- Aujeszkys disease in pigs - eradicated from UK but could return
- Bovine infectious rhinotracheitis (IBR) = common
What’s in the normal cat vaccine?
- cat flu = feline herpes virus and 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 on a single molecule (mostly small point mutation)
Where are is RNA found and how does it allow for faster mutations?
- different molecules and segmented allows for faster mutations
Which has a higher mutation rate - DNA or RNA?
- RNA
Are DNA viruses stable or unstable?
and by process of elimination what are RNA viruses?
- DNA viruses are stable
- RNA viruses are unstable
Positive sense vs negative sense are to do with what?
- to do with ability to produce viral proteins directly or through intermediate stage
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 such as 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
What viruses can a capsid be 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
- helical
- complex
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?
- all 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?
= 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
- must sat wet
- 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
Hosts can develop antibodies against glycoproteins if what is present?
-
What is a non-structural protein?
- Not part of structure often enzymes
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
