Lecture 3D - Viruses Flashcards
What is the genetic structure of viruses?
they are acellular
they contain DNA and RNA
How do viruses reproduce?
inside cells and rely upon the host cell machinery to survive and reproduce
What are prions?
a novel form of infectious proteins which have no DNA at all
Why can prions (and maybe viruses) not be considered as independent living organisms?
they do not possess the machinery to reproduce themselves, but require intracellular enzymes, metabolic pathways and organelles in order to reproduce
What are viruses?
non living obligate intracellular parasites that need a host cell in order to replicate
How do viruses contain genetic info?
they possess their own genetic info in the form of RNA or DNA
What form do viruses also have?
an extracellular form
What can viruses infect?
all types of cellular organisms including plants and animals
What are some strains of virus associated with?
increased risk of cancer
What happens if viruses have genetic information in the form of RNA?
usually it will have to be reverse transcribed back to DNA in order for the virus to replicate
What are the aims of infectious virus particles?
to be able to invade a host cell to replicate and to be able to transmit from one host organism to another
What are successful viruses?
they tend to not kill their host, as it does not help the survival of the viral strain
How are polio and hepatitis A transmitted?
faecal-oral route
How is rabies transmitted?
bite of an infected animal e.g. rabid dog or bat
How is human papilloma virus (warts) transmitted?
skin contact
How is herpes 1&2, HPV, hepatitis B and HIV transmitted?
sexual transmission
How is ebola transmitted?
all body fluids and tissues
How is influenza, colds, measles, mumps, rubella transmitted?
respiratory
How is yellow fever, dengue fever, chikungunya virus transmitted?
insect vectors
What is COVID-19?
a coronavirus which can cause severe acute respiratory syndrome
Extracellular form viral structure?
diverse sizes, shapes and chemical composition
nucleic acid surrounded by protein coat (capsid)+/-lipid envelope
mainly rod shapes with a helical nucleic acid or icosahedral with spherical nucleic acid
What do viruses have surrounding their icosahedral shape?
filamentous fibres
What do viruses have at their core?
their genetic material, either DNA or RNA
and often some enzymes needed for cell entry during infectin and replication
What are viruses with RNA?
retroviruses, the RNA needs to be reverse transcribed in order for the virus to replicate
What is the lipoprotein bilayer on a virus?
envelope (some viruses)
derived from the host
What viruses have lipoprotein bilayer?
DNA = hepatitis B RNA = rabies, rubella
What is the protein shell?
the capsid - nearly all viruses have this
this encapsulates their genomic material
Naked viruses?
DNA = papilloma RNA = hepatitis E
What do the glycoprotein spikes do?
they bind to the target protein in the host and trigger the sequence of events which enables the virus to enter the cell
Size of the largest viruses?
300-400nm across with a 100nm layer of filamentous fibres surrounding their icosahedral shape
Size of COVID-19 virus?
50-150nm in diameter without the spikes
DNA virus replication?
when the DNA is inserted into the host cell, it uses the host cells RNA polymerase to make mRNA, which is the translated by the ribosomes of the host cell
RNA virus replication?
have several ways to replicate
some carry their own RNA polymerase to produce mRNA
some have to carry out an additional step so that the negative or antisense) RNA is converted to positive (sense) RNA, from which mRNA is made
What do retroviruses have to do?
reverse transcribe their RNA into DNA which is then inserted into the host cell genome
How does a virus with a lipid envelope leave the cell after replication?
it wraps itself in the membrane and buds off from the cell, to then travel onto the next target cell
How does a virus without a lipid envelope leave the cell?
it escapes by rupturing the cell membrane (cytosis) as it is released, killing the host cell
it is therefore cytopathic
What are prion protein diseases?
rare, fatal neurodegenerative diseases belonging to amyloid group
What do prion protein diseases affect?
Humans (Creutzfeld jacob disease) and agricultural, zoo and wild animals
Examples of prion protein diseases?
scrapie in sheep
bovine spongiform encephalopathy in cows
chronic wasting disease in elk and deer
Aetiology of prion protein diseases?
genetic, sporadic and infectious
Incubation period of prion protein diseases?
they can have lengthy incubation periods >40 years!
Clinical characteristics of prion protein diseases?
dementia and ataxia
neuronal loss, gliosis and spongiform change in the brain
Immune response to prion protein diseases?
no classical host immune response
Treatment of prion protein diseases?
currently no treatments available for the disease, has to be managed by trying to eliminate the spread
What is a marker of astrocytic gliosis?
glial fibrillary acidic protein
What is detected by antibodies?
the prion protein
What is one of the characteristic of prion diseases?
the accumulation of aggregates of abnormally folded prion protein (PrP)
Structure of the normal prion protein PrPC?
3% beta sheet
monomeric and soluble
protease sensitive (PrPsen)
neuroprotective
Structure of infectious form of the prion protein (PrPSc)?
disease associated form
43% beta sheet
aggregated and insoluble
partially protease resistant (PrPres)
infectious, toxic
What is the infectious agent of prion disease not associated with?
any nucleic acids
there is no detectable viral agent in the infectious particle
Why is PrPC easy to break down?
it has a relatively open structure
What happens when the aggregates of PrPSc are formed?
they are hard to break down and can induce normally folded prion protein to misfold, propagating the number of infectious particles
Prion hypothesis?
prions are transmissable particles that are devoid of nucleic acid and seem to be composed entirely of a modified protein (PrPSc)
How is PrPC converted to PrPSc?
through post translation process during which is acquires a high beta sheet content
What do prions appear to encipher?
strain-specific properties in the tertiary structure of PrPSc
How is PrPSc broken down?
it is protease resistant and can only be broken down at a very slow rate by the cell
What does the misfolding of PrPC require?
the assistance of an additional unknown chaperone protein called protein X
(stanley prusiner 1998)
What does prion mean?
a protein only infectious agent
