Viruses 2 Flashcards Preview

Respiratory > Viruses 2 > Flashcards

Flashcards in Viruses 2 Deck (35)

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?



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