What are bacteriophages?
obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic material.
What is a lytic or virulent phage?
replicate only via lytic cycle
phage that can only multiply within bacteria and kills the cell by lysis
What is a lysogenic or temperate phage?
replicate via lytic and lysogenic cycle
a phage that can either multiply by lytic cycle or enter a quiescent state in the bacterial dna
What is PhiX174?
- isometric virus with 20 triangular faces
- microvirus
- first to be sequenced
- sense circular ssDNA
- v.small genome of 5000ish nucleotides
- genome infectious by itself
- model for DNA replication
- replication occurs via dsDNA
- some genes overlap
- 4 distinct intergenic regions
What is the life cylce of PhiX174?
- attatchment of virus to bacterial host followed by injection of ssDNA
- due to genomes pos polarity, DNA replication must commence before viral genes can be transcribed
stages.
1. ssDNA->dsDNA
2. amplification of ds molecule
3. ss genomic DNA synthesising and packaging.
What are M14 of F1 phages?
filamentous phages that infect E.coli through pilo and are able to produce new virions without lysing host cell
- circular, ssDNA
- 6.4kb long
- 10 genes in genome.
What are lambda phages?
bacteriophages that infect E.coli nibbled and plaqued by E.coli temperate life cyce lyses cell to produce offspring. *has fast replication cycle during lytic cycle, consists of eclipse period, intracellular accumulation phase lysis and release phase.
What is T4?
Bacteriophage
order:calidoivirales
family myovirdae
*complete genome sequence of 170,000 ishh bp
- encodes about 300 genes
- does not encode RNAP
- phage encoded proteins do sequentially modify ost RNAP
What are CRISPR?
clusters of regularly interspersed short pallindramic repeats
segments of prokaryotic DNA containing short repetitions of base sequences
Each repetition is followed by short segments of “spacer DNA” from previous exposures to a bacterial virus or plasmid.
CRISPRs are often associated with cas genes that code for proteins related to CRISPRs.
CRISPR/Cas system is a prokaryotic immune system that confers resistance to foreign genetic elements such as plasmids and phages
CRISPR spacers recognize and cut these exogenous genetic elements in a manner analogous to RNAi in eukaryotic organisms
What is phage display?
a lab technique or the study of protein protein dna interactions using bacteriophage.
Give an example of bacteria/bacteriophage arms race?
- bacteria have restriction system to protect themselves
- entering DNA is methylated by a modification enzyme and becomes resistant to degradation by restriction endonuclease
- Restriction enzyme cleaves foreign DNA before it has the chance to be methylated.
What affect can some phages have on bacterial host?
some lysogenic phages carry genes that can enthance the virulence of the bacterial host
eg. some phage carry genes that encode toxins
make once harmless bacteria harmful once interfrated into bacterial chromosome.
What are examples of virulence factors carried by phages?
cholerae toxin - chloera. CTX phage
shigalike toxin - hemorrhagic diarrhea - lambda phage
food poisening - clostridial phage
erthogenic toxins - scarlett fever - T12
Describe the lytic cycle
Lytic
- the phage is a free floating separate molecule to the host DNA and replicates separately from it.
- spread through the production of thousands of individual phages capable of surviving and infecting other cells.
Describe the Lysogenic cycle?
- phage DNA first integrates into the bacterial chromosome to produce the prophage.
- bacterium reproduces, the prophage is also copied and is present in each of the daughter cells.
- the daughter cells can continue to replicate with the prophage present or the prophage can exit the bacterial chromosome to initiate the lytic cycle
- lysogenic cycle does not lyse cell.
What do both the lytic and lysogenic cycles have in common?
they both use the hosts biosynthetic material.
