Viruses 2 Flashcards
What is the eclipse period in virus growth?
The period of time when it appears like there isn’t any virus present because it has infected a cell and been broken down to its components
What is the latent period in virus growth?
The period of time up until the first appearance of the virus extracellularly
What are the stages of viral replication?
Attachment, penetration, uncoating, genome replication, RNA synthesis, protein synthesis, assembly, release
How does a virus attach to its host cell?
By interacting with a physiological receptor on the plasma membrane
How does HIV gain access to the cell?
HIV has two proteins gp41 and gp120. The peptide on the end of gp41 is very hydrophobic. The CD4 receptor on the CD4 cell binds to gp120 to capture it. This induces a conformational change which forces the hydrophobic region into the extracellular environment and allows the CCR-5 receptor on the CD4 cell to bind to the gp120 protein. Then the hydrophobic peptide of gp41 inserts into the plasma membrane and drags HIV in closer until the viral envelope merges with the plasma membrane and the genome is released into the cell.
What are the two ways which a virus can penetrate a cell?
Viral envelope fusing with the plasma membrane or enter via endocytosis - which then requires exiting from the endosome by exposure of a hydrophobic region or by lysis of the endosome
Where do DNA viruses usually replicate?
The nucleus
Where do RNA viruses usually replicate?
The cytoplasm
What is a DNA virus that doesn’t replicate in the nucleus?
poxvirus
What is an RNA virus that doesn’t replicate in the cytoplasm?
influenza virus
What kind of proteins are made first by RNA?
non-structural proteins
What does a DNA virus use for replication?
The host cell’s DNA dependent DNA polymerase
How does a + sense RNA virus replicate?
The genome translates its proteins using host mechanisms and synthesises its own RNA dependent RNA polymerase
How does a - sense RNA virus replicate?
By bringing their own RNA dependent RNA polymerase with them into the cell
What is class I in the Baltimore Classification?
ds DNA viruses
What is class II in the Baltimore Classification?
ss DNA viruses
What is class III in the Baltimore Classification?
ds RNA viruses
What is class IV in the Baltimore Classification?
+ sense ss RNA viruses
What is class V in the Baltimore Classification?
- sense ss RNA viruses
What is class VI in the Baltimore Classification
retrovirus - creates DNA from RNA by carrying a reverse transcriptase with it - so that it can integrate with the host cell genome
Why does the poxvirus have to carry its own DNA polymerase?
Because it replicates in the cytoplasm
How is translation of proteins done by viruses?
By using host cell ribosomes
How is post translational cleavage of polyproteins done by viruses?
Usually by virus coded proteases
How is glycosylation of envelope glycoproteins done by viruses?
Using the host cell RER and golgi
How do non-enveloped viruses assemble?
By spontaneous assembly to form the energy minimised state or by assembly mechanisms
How do enveloped viruses assemble?
By budding through the cellular membrane or by secretory pathway of the cell
What are the four possible outcomes of the cell after infection by a virus?
Tumor formation, lysis, release without cell death or a latent infection where virus remains in the cell
What are cytopathic effects?
Changes seen under the microscope created by viruses
What cytopathic effect do adenovirus infected cells have?
Nuclear inclusions
What cytopathic effect do reovirus infected cells have?
Cytoplasmic inclusions
What are oncogenes?
Genes encoded by the virus which promote growth in the host cell and lead to uncontrolled proliferation
How do viruses evolve?
Either by mutation, recombination or reassortment (segmental genome)
Why are RNA viruses prone to mutation?
Because their RNA dependent RNA polymerase doesn’t have a proof reading mechanism
How does the body halt the infectious process?
- antibodies to block uptake or neutralise progeny
- killing by NK cells, cytotoxic T cells or antibody mediated mechanisms
- interferon - turns on antiviral mechanisms
- antiviral drugs that block the replication cycle
What is one way in which antiviral drugs are different to antibiotics?
Antiviral drugs are very specific for a certain virus because each virus has a different replication strategy
