Bacteriophages Flashcards
What are the 4 types of phage classification
Ds dna
Ss dna
Ss rna
Ds rna
What happens to dna if it’s ssdna
Replicated then converted to mrna +
Name a ss dna phage
M 13
Why wouldn’t M13 ds dna show up as a PFU
Has no cytopathic effects
It is released without lysis
What is ss dna phages like M13 used for and why
Gene cloning as vectors
They have space in genome for the gene of interest
what is phage displaying usually done on ss dna like M13
It is insertion of the gene (cloning) to detect its function when infecting bacteria
Which phage is most common and give example
Ds dna
Eg T4
What is the advantage of SSRNA (+)
It doesn’t have to be converted to mrna as already sense
It can be translated straight away
What do Ss rna (-) phages use (different in viruses)
Use rna replicase converting it to + mrna
What allows a phage to attach
Tail fibres
Which enzymes allow entry into the bacteria and also exit
Lysozymes
What allows injection of nucleic acid into bacteria
Receptor recognising the phage
Which period can’t detect phage in it outside of the cell
Eclipse period
What is the lag phase in phage graphs
The bottom line
It is the period where the maturation of virion occur before lysing
What is the rise period
The exponential growth where the phage has lysed
Shown on graph
At what phase do PFU stop increasing (after rise period)
Plateau period
What is the name for number of phages released from 1 cell
Burst size
How do you work out burst size
PFU highest value / PFU lowest value
Are T4 ds dna phages lytic?
Yes
What happens to all of the dna when injected
Both host and phage dna are hydrolysed before assembly
At what point does lysozyme production occur/ translation/ assembly
At the exponential phase - causes lysis
What is the main lysogenic phage called
Lamda
What are lysogenic lamda phages good for
Transfer pathogenic/ virulence to the bacteria chromosome
What is it called when the lysogenic lamda genome is incorporated to host chromosome
PROPHAGE
What is a lysogen
Phage which dna is replicated within the host chromosome as a prophage
Which protein in high numbers causes flip to the lysogenic phase
Cl protein
Which protein causes a flip to the lytic cycle
Cro protein
When would lysogenic cycle be favoured
If bacteria are in harsh conditions and not likely survive
Why can lamda phages be used for cloning alongside M13 (ss dna)
1/3 of its genome can be replaced with a gene of interest
Why is T7 used for cloning
They have a specific T7 rna polymerase which only works alongside specific promoters
Used for manipulating expression of genes
Why can phages be used as alternative to antibiotics
Kill bacteria (phage therapy)
And useful in stopping biofilms eg in toothpaste
