Virology introduction Flashcards
Are humans more closely related to bacteria e.g. E.coli or viruses?
We are far more closely related to E.coli than some viruses are to one another because viruses are massively variable -by grouping them it helps us to understand them
What is the definition of a virus?
Obligate intracellular parasite - they can’t replicate on their own, they require replication machinery of their host cell
They are essentially a protein shell protecting nucleic acids
What are viroids?
very small rod-like RNA molecules, only plant pathogens - they have no protein outer shell = therefore they are not viruses
What are prions?
no nucleic acids, therefore they are also not viruses
- resistant to heat inactivation
- resistant to radiation damage
- resistant to DNAse and RNAse treatment
- Sensitive to urea, SDS, phenol and other protein-denaturing chemicals
What are the key facts to know about viruses?
1) can’t replicate themselves - do not contain cells of any sort (acellular)
2) Cannot make energy or utilise nutrients
3) cannot synthesise anything
4) depend entirely on the cell they infect for all of these functions
What is the Baltimore system?
System of grouping viruses
- based on what is within the cell free particle
1) dsDNA viruses e.g. Herpes virus
2) ssDNA viruses e.g. parvovirus
3) dsRNA viruses e.g. rotaviruses
4) (+) sense RNA viruses e.g. HCV, polio
5) (-) sense RNA viruses e.g. influenza, ebola
6) RNA reverse transcribing viruses e.g. HIV
7) DNA reverse transcribing viruses e.g. HBV - strange virus which means all the groups are divided up with 4 groups of RNA viruses and 2.5 groups are DNA
What is the key difference between all organisms compared to viruses?
All organisms contain DNA and RNA but viruses contain RNA or DNA - never contain both
In simple terms, what do viruses look like?
nucleic acids surrounded by a capsid of proteins to protect the nucleic acids from nucleases
What are the 2 basic structural types of viruses?
Simple and complex
Simple - round or helical, clear symmetry
Complex - no clear symmetry
Viruses cannot be classified by shape like bacteria are
Where do you find helical capsids and what do they look like?
> 90% of viruses but no human viruses with human capsids - only measles and rabies have slight helical structure but don’t form the straight rods
Wedged shaped proteins that are all exactly the same - create an angle of 22 degree
360/22 = 16.3 therefore the 17th protein can’t fit in properly therefore the wedges go up in a spiral
What structure do most human viral pathogens take ?
Icosahedral capsids >90% of human pathogens = 20 triangles arranged in a sphere - internal surface if these triangles are basic and attract acidic DNA or RNA
This structure is much more size constrained so they is a limit to the genome size unlike helical capsid structured viruses
What host proteins within the central dogma does the virus to advantage of?
DNA polymerase
RNA polymerase
Translation machinery
Which viruses plug in to use RNA polymerase?
dsDNA - plug straight into transcription machinery to create products
Which viruses plug in to use translation machinery?
+ssRNA - plug in straight away and start making RNA products
Which viruses plug in to use DNA polymerase?
ssDNA - only need to replicate first and then they use all host machinery
How do host cells replicate RNA viruses?
When the RNA virus infects a cell it also brings along their own RNA polymerase to make
What do antisense and double stranded RNA viruses have to do when they enter the host cell?
they have to make transcripts before they can start making proteins
What signalling do obligate intracellular parasites/viruses always trigger first ?
intracellular sensing = CD8 and CTL
Whereas their extracellular signalling occurs later = CD4 and antibodies
Virus/parasites are presented on MHC class I - these molecules are present on all nucleated cells, therefore all cells have the potential to be infected
What is the consequence of cells infected by an extracellular signal being leaky?
It means that although an infections (eg virus) can be leaked across into MHC class 1 system to generate a cytotoxic T lymphocyte response after they have already induced a CD4 response
What do endogenous and exogenous antigens prime?
Endogenous can prime CD4 (class 2) Exogenous can prime CD8 (class 1)
What are the key mechanisms of actions of directly neutralising antibodies?
Block virus/receptor interaction
Block endocytosis
Block release into cytoplasm
Aggregate virus
- almost all neutralise at the cell surface = lots of vaccines take advantage of this method
What is the link between vaccination and B memory cells?
Immunological memory e.g. B memory cells normally develop during/after an infection
Vaccines are artificial ways of introducing memory against a pathogen - therefore vaccines are mimics of the natural response
What are the 2 major traditional types of vaccines and what are the 2 major new types?
Traditional
1) Live attenuated (BCG, OPV, MMR)
2) Inactivated (pertussis, IPV)
New
1) Recombinant protein (HBV)
2) DNA based (experimental, flu)
What are the features of effective vaccines?
Safe- don’t cause the illness itself
Protective- effective against illness occurring upon exposure to live pathogen
Gives sustained protection - lasts several years
Induces neutralising antibody- stops pathogen infecting cells
Induces protective T cells- particularly intracellular pathogens are more effectively dealt with by T cells so their vaccines induce at cell mediated response
Practical considerations - low cost per dose, biological stability, ease of admin, minimal side effects
