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 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
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