Viruses Flashcards
what do viruses do
- Infect all living things
- Come into contact with viruses through water food air
- Viral genomes are part of our genetic material
what are the 7 different viral families
- Paramyxoviruses 11 types
- Adenoviruses 14 types
- Arboviruses 8 types
- Coronaviruses 4 types
- Novel polyomaviruses 3 types
- Bocaviruses 2 types
- Herpesviruses (many new)
what is the most common human viruses
- Herpesviruses
how many viruses are known to infect humans
- Greater than 200 viruses but not all of them are harmful
- Any tissue in the body can pretty much be infected
Define a virus
- A package of genetic information protected by a protein shell for delivery into a host cell to be expressed and replicated
- They are obligate intracellular parasites that cannot be desicbred as either dead or alive
why is the protein shell important
- Infect other cells
- Identify cells that it can infect
- Protect it from the innate immune system
- Protects itself from the restriction factors
virus classification system
- Kingdom
- Phylum
- Class order – virales
- Family – viridae - paramyxoviridae
- Genus – virus - morbillivirus
- Species – measles virus
How do you classify viruses
Baltimore classification system
whats the defining feature feature of the Baltimore classification system
needs to get to mRNA
- because if you want to make proteins you have to get to mRNA
what is the Baltimore classification system
- I: dsDNA viruses - (e.g. Adenoviruses, Herpesviruses, Poxviruses) double stranded DNA viruses – can make DNA
- II: ssDNA viruses (+)sense DNA (e.g. Parvoviruses) 0 single stranded DNA virsues – must go to double stranded
- III: dsRNA viruses (e.g. Reoviruses) – double stranded RNA viruses – can make mRNA directly
- IV: (+)ssRNA viruses - (+)sense RNA (e.g. Picornaviruses, Togaviruses, SARS-CoV) positive strand single stranded RNA – needs to go to negative then make mRNA
- V: (-)ssRNA viruses – (-)sense RNA (e.g. Orthomyxoviruses, Rhabdoviruses, Flu) – can be used directly
negative single stranded RNA - VI: ssRNA-RT viruses single stranded RNA - reverse trasncirbe RNA into DNA and hten make mRNA (+)sense RNA with DNA intermediate in life-cycle (e.g. Retroviruses)
- VII: dsDNA-RT viruses – double stranded RNA - reverse trasncirbe RNA into DNA and hten make mRNA(e.g. Hepadnaviruses)
describe other classification of viruses
- If they have DNA or RNA as their genetic material
- Their genetic material is single stranded or double stranded, sing stranded RNA viruses can have either positive or negative sense RNA
- Their capsid is shaped as helix an icosahedron or has a complex structure
- Viruses has an envelope surrounding it or not
what makes up the viral structure
glycoprotiens
envelope
caspid
nucleus
describe the envelope as viral structure
– derived from the host cell membranes (cell surface membrane, ER and Golgi) presence of envelope means it is easier for the virus to enter host cells this increases the infectivity, viruses that are enveloped are more prone to environmental stresses such as heat and acid
describe the capsid as viral structure
made up of capsomeres, protects the DNA and RNA from nucleases and acts as antigen in virus lacking envelopes
describe the nucleus as viral structure
- Nucleus contains the genetic material and necessary enzymes required for its translation and replication
describe the golgi as viral structure
act as attachment points to host cells, help viruses fuse with the host cell memrbane and enter the cell – glycoproteins are usually also the antigens which the immune system recognises to mount an immune response, glycoproteins can only bind to specific types of cells
what is the information within a viral genome
- Replication of viral genome
- Assembly and packaging of the genome
- Regulation and timing of the replication cycle
- Modulation of host defences
- Spread to other cells and host
what is the functional of structural proteins
- Protect the genome
- Recognise viral nucleic acid for packaging
- Deliver viral nucleic acid to host cells
- Many shapes and sizes produced by evolution
what are the different types of capsids
- Helical – e.g. tobacco moascic virus, has to have a protien on the RNA in order to stay there, helcal – wraps itself regulary around the RNA
- Icosahedral - has 20 sides, mathematically the best shape to make a capsual of that size
- Complex
How do capsids acquire envelopes
The capsid takes up the right nucleic acid that is the genome of the virus
Goes to cell surface
Protein envelope of the virus is being made in the cell
They specifically meet each other at the same place in the cell surface
Have viral glycoproteins on the outer surface – spikes
The nucleic acid recognises a specific cell type – and the envelope glycoprotein is specific to recognise the cell type – it takes it to the cell that it is required in
- Lipid envelopes are derived from cellular membranes
- Studded with surface projections, spikes or peplomers
- These are usually glycosylated by host systems prior to make them sticky
what cells does viral replication take place in
susceptible and permissive
describe the cell types associated with viral replication
Susceptible cell – has the functional receptor for the virus, the virus can enter the cell Resistant cell – No receptor, virus cannot get in Permissive cell – has the capacity to replicate the virus
describe how viral infection and replication happens
- Host cell membrane receptors interact with viral glycoproteins/capsids
- Viral and host cell fusion
- Capsids opens to let genetic material into the cell – this can happen through different mechanism such as reduced pH in lysosomes
- Viral DNA or RNA hijack translation machinery to make viral proteins
- DNA or RNA is replicated
- DNA or RNA together with the capsomers form a virion (same thing as a virus)
- Virions exit the cell through budding or cell lysis (cells that exit through budding also get an envelope from the cell surface memrbane)
what is viral replciation divided into
- Can be divided into whether they complete their replication in the cytoplasm (most RNA virsues expect retroviruses and orthyomyxoviruses plus poxviruses or whether they complete their replication in the nucleus – most DNA viruses except poxviruses plus orthmyxovirsues
- Both compartments retroviruses such as HIV and hepadnaviruses
