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Flashcards in Viruses Deck (24)
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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

-Into nucleocapsids
-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?

-Coated pits
-Fusion with pm


What 4 effects can viruses have on cells?

-Cytopathic effects
-Cellular death
-Chromosomal damage
-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
-Cellular lysis


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

-Hepatitis B
-Small pox


Name a naked DNA virus



Name an RNA enveloped virus



Name a naked RNA virus