Virology 4 Flashcards
(41 cards)
Stages in virus life cycle
- Adsorption
- Penetration
- Uncoating
- Replication & gene expression
- Assembly
- Release
Bacteriophages discovered by who
- Twort & d’Herelle
who showed that it was DNA not protein that carries genetic info
Hershey & Chase, 1952
Why is there renewed interest in phages as therapeutic drug
Due to AMR
Outcome of lytic infection
Produces bacteriophage virion particles & results in cell lysis
Outcome of Lysogenic infections
- Phage integrates into bacterial genome and replicates w cells
- Doesn’t produce bacteriophage virion particles
- Spontaneous/stress induced induction into lytic cyle - cell lysis
Outcome of chronic infections (filamentous phage)
Produces bacteriophage virions w/o destroying the host cell
What is the phage DNA inserted into the bacterial host genome
Prophage
2 phages that are temperate
- Lambda
- Mu
Difference between lytic and lysogenic phages: which can kill host?
- Lytic cycles both kill & solubilise host bacteria
- Lysogenic phages dont kill host bacteria unless lytic cycle induced
What are temperate/lysogenic phages agents of
Horizontal gene transfer (including virulence genes)
What is transduction
The transfer of genetic material from one bacterium to another by viral (phage) vector
Generalised transduction
DNA derived from any portion of host genome is packeged inside the mature virion in place of the virus genome
(normal lytic events before this - upon lysis normal phage & transducing phage (w/ host cell DNA) released)
Specialised transduction
- DNA from specific region of host genome is integrated directly into virus genome, replacing some of the viral genes
- Only in certain temperate viruses, e.g: Lambda phage
WHat kind of phage does specialised transduction occur in
Certain temperate viruses - phage lambda
How to quantify viruses in lab
- Mix of agar, bacterial cells, diluted phage poured onto plate
- phage plaques form
- count & multiply by dilution factor
- no. of viruses as PFUs (plaque forming units)
(could also do qPCR)
what does the one step growth curve measure
Measures how a virus infects cells, replicates & releases new virions over time
5 phases in one step growth curve for virus/bacteriophage
- Eclipse phase
- Maturation phase
- Latent phase (eclipse & maturation)
- Burst phase
- Plateau phase
Eclipse phase
Virus particles internalised & being replicated but not yet detectable
maturation phase
Newly made genomes being packaged into capsids
Latent phase
- eclipse & maturation collectively
- newly assembled virions not yet present outside cell
Burst phase
Increase in virus particles as newly assembed virions released
Plateau phase
virus production levels off once all host cells are lysed/exhausted
Possible effects of viruses on human/animal cells
- Transformation of normal cells to cancer cells - HPV
- Lytic infection - Herpes Simplex Virus 1 & 2
- Persistant infection - Hep B & C virus
- Latent infection - Herpes Simplex Virus 1 & 2, HIV
