viruses and bacteriophage Flashcards
describe the structure of viruses
- a piece of nucleic acid (could be DNA, RNA, ds, ss, circular, linear) sorrounded by a protein capsid
- sometimes there are lipids
why is it so hard to create antivirals
there are so few components
are viruses cells
no; they’re obligate parasites
-they have no ribosomes so cant replicate themselves; they use another cells resources
how big are virus genomes
5-1000 genes
which proteins do virus genomes code for; name 3
only those genes that cant be stolen from the host and those that are absolutely necessary;
i) lysozyme to enter cell
ii) reverse transcriptase if genome is RNA
iii) DNA polymerase
name animal, plant and bacteria viruses
animal; HIV, influenza
plant; tobacco mosaic virus
bacteria; lambda bacteriophage
discuss the lytic replication cycle
- virus nucleic acid enters cell and leaves its protein capsid outside
- nucleic acid remains extrachromosomal replicates its nucleic acid and synthesises viral protein particles own circular DNA which is then cut at cos sites
- the nucleic acid is packaged into particles before lysing the cell and bursting out to infect other cells
what are the usual characteristics of a bacteriophage
dsDNA
naked; protein and nucleic acid
what is lambda
- a bacteriophage virus which infects e.coli cells
- docks to maltose on a cell membrane using its tail fibres
- pushes DNA from head, through tail into the cell while the protein remains outside the cell
discuss the two life cycles of lambda
for both cycles the virus inserts only the DNA which then circularises
lysogenic; DNA incorporates itself into the genome and is passed on via vertical transfer to daughter cells
-can leave lysogenic cycle and enter lytic cycle due to stress etc
lytic; nucleic acid remains outside of the e.coli genome and is expressed as capsid protein using e.coli ribosomes.
-the e.coli DNA is digested and the virus then replicates its own Dna and packages it into the capsid before lysing the cell wall and bursting out of the cell
what is a cryptic virus
a virus that becomes so mutated it cant remove itself from the host genome
this sometimes happens when the viral DNA has been incorporated for many generations
how are viruses grown
- grown on a lawn of e.coli which have been grown on the culture medium
- a plaque is an area where a single virus has killed the sorrounding bacteria and divided
- titre; number of viruses per unit
how is the viral growth curve different to the bacterial growth curve
bacterial;lag, log, plateau
viral;eclipse (decrease in titre as phages enter bacterial cells), sudden rise, plateau
discuss how viruses provided evidence for the fact that DNA contains genetic material and not proteins
- many people believed that protein contained genetic information because DNA only has 4 bases whereas proteins are much more complicated
- in two different experiments, viruses either had their phospherus labelled red or there sulphur labelled blue (phosphorus only appears in DNA and sulphur only appears in protein)
- bacteria were infected then centrifuged so that bacterial cells were pelleted and viruses were in supernatent; pellet was red and supernatuent was blue suggesting that protein was left outside of e.coli
discuss some possible uses of bacteriophages
1) phage therapy; engineer genes that would be transferred to a host to cure a disease
2) clone DNA
3) cDNA and genomic libraries
4) removal of biofilms;engineering dispersinB into bacteriophages
what are the 4 advantages of bacteriophages
1) are very specific and target specific cells
2) rely on bacteria to grow so when bacteria grow so do they
3) evolve faster than abcteria
4) penetrate deap wounds
what are the 6 drawbacks of phages
1) public scepticism due to origin; originally found in seweges
2) using lysogeny cycle creates possibility of horizontal transfer
3) they are so specific that using them clinically requires deep investigation of the bacteria causing the problem; this means often a cocktail of bacteriophages are used; not scientifically sound and doesnt establish cause and effect
4) hard to get IP for them so difficult to get a return on investment; remain unexplored
5) often are removed by host immune system; if theya re to be used clinically they need to act fast
6) bacterial lysis sometimes leads to host inflamation and ill health
