Week 2 Phage's Flashcards
Give a brief overview of bacteriophages
2 main structures: head and tail, Filamentous
They are viruses that infect bacteria
Can have DNA or RNA which can be DS or SS
Encode proteins for replication of the virus
Usually specific for certain bacterial hosts
List the main types of phage life cycles
lytic - fresh particles are rapidly produced before being released via cell lysis
Lysogenic - Replicates phage genome without destroying the host
Phages that have both are called temperate phages
while phages that only have lytic cycle are virulent phages
How do lytic phages react when plated on agar?
they form plaques (Zone of clearing) in bacteria lawns
lytic lifecycle of bacteriophage Lambda
- Virions bind to surface receptor LamB
- Phage DNA injected into cell
- Replication of DNA
- capsid components are made, DNA packaged, New phages assembled
- Phages released via lysis
Lysogenic life cycle of Lambda phage im E. coli
- Virions bind to surface receptor LamB and inject DAN into cell
- Phage DNA circularizes
- Phage DNA integrates into bacterial chromosome
- Phage DNA is replicated as part of the bacterial chromosome
- lysogenic state stable until phage DNA is induced to excise from the chromosome
Reactivation from lysogenic to lytic life cycle and its causes
- lambda DNA excise for bacterial chromosome
1.5 lytic processes activated - phage DNA is replicated - components assembled - virions released via cell lysis
Can be caused by:
UV light
ROS
DNA damage
Antibiotics
What is transduction and its use?
It is a method for transferring DNA used by a phage it occurs when a phage packages a portion of the host genome instead of its own, with this genes can be donated to other bacteria
Steps of generalised transduction?
- genes of interest present in donor
2.phage infects donor undergoes replication - host genome becomes fragmented
- some fragments become packaged in phage virions
- phage carrying donor DNA are released
- Phages infect a recipient bacterium that lacks the gene of interest
- fragments may recombine with homologous region in recipient genome
What is the packaging limits for Phage Lambda?
it is 52kbp of DNA with the lambda genome being 49kbp meaning there is space for 3kbp
Give an overview of the need and creation of lambda phage insertion vectors
lytic phages have a large segment of genes involved with integration into the chromosome which is not needed for lytic lifecycles, so it is removed with RE this takes the size of the genome from 49 kbp to 35-40 kbp
