Viruses Flashcards
What is a virus?
An intracellular obligate parasite
What is the structure of a virus?
Nucleic acid genome that forms three genes, protected by a capsid and an external envelope. No membrane bound organelles for protein synthesis so require a host
How are viruses classified?
Via their genome which will either be DNA or RNA and Double or Single stranded and Sense or Antisense
What is required to convert antisense to sense?
RNA polymerase converts before translation can occur.
Give the type of genome associated with each classification I-VII.
I - DNA Ds e.g. adenovirus, herpes simplex
II - DNA Ss e.g. parovirus
III - RNA Ds e.g. retrovirus
IV - RNA Ss sense RT e.g. Hep C, polio
V - RNA Ss antisense e..g. influenza, ebola
VI - RNA Ss sense TR e.g. HIV
VII - DNA Reverse transcriptase e.g. Hep B
What shape can capsids be?
Helical e.g. ebola
Cosahedral (20 triangles into a sphere) e.g. adenovirus
What is specific to retroviruses?
Must make a DNA reverse transcript from its RNA genome to integrate into the host’s genome. This makes the infection irreversible e.g. HIV
What happens once a cell is infected?
The viral capsid dissembles and control over synthesis of viral proteins begins
What features does the viral synthesis produce?
Replication factors produce non-structural proteins
Subunits which assemble for form structural proteins for the capsid and virions.
Viral genome is copied.
What is the eclipse phase?
The phase in which components are synthesised and new generations assemble. The virus cannot be recovered in this phase as it is latent.
How are the new viruses released?
Via budding or lysis within minutes or days.
What determines the burst size?
The presence of a lipid membrane.
A small burst is due to a membrane slowing the replication and the spread is slow.
A large burst size is due to the lack of a lipid membrane and the virus spreads fast.
What is tropism?
The binding of a virus to a specific surface receptor of the host.
What determines if a species is resistant to a virus?
The presence of the specific receptor required to infect
What is the tropism of HIV?
HIV GP120 binds to CD4 and CCR5 on macrophages and CD4 T cells causing gradual destruction of the immune cells, progressing to AIDs. Only if bound to both types of receptors will invasion occur.
What is the mechanism of infection of a non-enveloped virus?
e.g. adenovirus and polio
Cytopathic so destroy host cell via LYSIS. Can cause chronic infection by production a low number of particles over a long period.
What is the mechanism of infection of an eveloped virus?
Uses BUDDING to release the virus directly or into vessels.
What test is used to identify the strain of virus?
ELISA - identifies antigens
PCR
What is the difference between a well adapted virus and a poorly adapted?
Well adapted wait until it has finished replicating to infect the host. The best will incorporate into germline via gametes.
New species are usually unstable and poorly transmitting so tend to disappear.
What is a latent infection?
An infection which resides within the nucleus of a host cell, producing no proteins but controlling mRNA transcripts. It is not recognised as no proteins are produced, allowing it to replicate slowly without immune recognition or symptoms.
How does Herpes simplex virus control a host cell?
Via miRNA
How does Human endogenous retrovirus use gametes?
Uses syncytiotrophoblasts to form its envelope and infect the host.
What is the prodromal response?
The commmon set of symptoms that present with a viral infection due to the general response of the innate immune system e.g. fever, headache, long bone pain due to haematopoeisis
How can a virus control a cell?
Decreasing cell synthesis, viral protein synthesis, permeabilisation of the membrane, virus assembly in cytoplasm, cell lysis and release.
What are the proteins of influenza?
Haemagglutinin and Neuramididase - can be present in a varying number combinations
What type of virus is influenza?
Unstable RNA virus.
How does the influenza virus change with time?
Antigenic drift = new pathogen produced by mixing and re-assortment of two strains of the virus together.
What is the mechanism of action of viral vaccines?
To block the cell attachment and preventing intracellular replication
