Flashcards in Viruses Deck (24)
What genetic information do viruses contain?
-DNA or RNA not both
-No genes which encode for proteins used in protein synthesis, ie ribosomes
-May/May not encode for enzymes involved in nucleic acid synthesis
Describe the different structures of DNA/RNA found in viruses
-Linear, circular nicked
-ss or ds
-ss can be +sense or -sense
-segmented or unsegmented
What is meant by +sense RNA and -sense RNA?
-+sense can be used directly as mRNA
--sense has to be converted to +sense to be used
Why does segmented DNA/RNA have evolutionary significance?
-Two viruses infect the same cell
-reassortment of segmented DNA/RNA may produce a more virulent form
Can viruses live outside of cells?
-No they are obligate intracellular parasites
How are viruses usually diagnosed?
-Through molecular detection of genome, i.e. PCR
-Through the detection of specific immune responses
How are all viruses arranged? Describe this structure
-Proteins arranged in a way which protects nucleic acid within from the harsh environment
-Helical or icosahedral
-Each individual subunit called capsomer
What is the major classification of viruses?
-Enveloped or naked
How are virus envelopes environmentally adapted?
-Contains lipids/glycoproteins which bind specific receptors on target cell membranes
-Glycoproteins mimic the host cell and the immune system cannot tell self from non-self
How are naked viruses protected from the human immune system?
-Virus infects cell
-Approaches pm and causes budding of the cell membrane in such a way that the virus becomes coated in cell membrane
-Cannot be recognised
What are the different viral classifications based on replication strategy?
-+RNAss -> directly translated
--RNSss -> converted to + to be translated as mRNA
--ssDNA -> has to be converted to dsDNA ->mRNA
-+ssDNA -> has to be converted to dsDNA->mRNA
-+dsRNA->has to be converted to dsRNA->mDNA
What is the inoculation period of viruses?
-asymptomatic replication stage of the virus which results in damage/dysfuction that is the symptom
How are viral infections described in terms of time?
-Acute, subacute, chronic, latent
What are the necessary requirements of a target cell for a virus?
-Must have appropriate cell surface receptors to initiate receptor mediated endocytosis
-Must have appropriate cellular machinery needed for replication
-After replication is successful, the cell must be permissive
What two other mechanisms, other than endocytosis, can viruses enter cells by?
-Fusion with pm
What 4 effects can viruses have on cells?
-Inhibition of cell protein synthesis
What are the cytopathic effects which viruses can have on cells?
-Inclusion bodies -> sites with active viral replication
-Syncytia formation-> giant multinucleate cells formed by fusion of pm
How are newly synthesised virus particles released?
-Bud from the cell
What must be necessary for a virus to cause cancer?
-Integration of all or part of the virus genome into the host cell
-RNA reverse transcriptase to introduce/activate oncogenes
-DNA viruses in non-permissive cells to deactivate tumour suppressor genes
What is the main cause of the resulting damage from infection?
-Inefficient host immune responses rather than microbe toxicity
Name a DNA enveloped virus
Name a naked DNA virus
Name an RNA enveloped virus