Lysogenic Phage Life Cycle Flashcards
Can all phages do the lytic cycle?
Yes
Can all phages do the lysogenic cycle?
No
What is lysogeny?
The process of a temperate phage integrating into the host genome
Does the phage get replicated when it’s integrated into the host genome?
No new phage get produced, but the viral DNA replicates every time the host divides
What is a prophage?
The viral DNA inside the host genome
What is a lysogen?
Bacterial cell with a prophage integrated into its genome
How does having a prophage alter the behaviour of Vibrio cholerae?
Only cells that have an integrated prophage cause cholera. The toxin gene is actually a viral gene and not a bacterial gene
Why would the lysogenic life cycle be advantageous to a virus?
Allows it to spread throughout the bacterial population without killing their hosts
What are the 9 steps of the lysogenic life cycle?
- Adsorption
- Infection
- Viral DNA circularizes
- Decision
- Expression of integrase and early gene repressor
- integration
- Host replicates
- Induction
- Lytic cycle
Why does the λ phage genome circularize once its in the cell?
COS sites - complementary sticky ends
What happens during the decision step of the lysogenic life cycle?
The phage “decides” to undergo the lytic or lysogenic cycle
What would cause a temperate phage to undergo the lytic cycle?
If the host cell was unhealthy, stressed, or starving
What would cause a temperate phage to undergo the lysogenic cycle?
If the host cell is healthy and not stressed
How does a phage “decide” to undergo the lytic or lysogenic cycle?
It can sense the cell’s environment and detect chemicals that indicate stress
Will plating bacteria on complete media favour the lytic or lysogenic cycle?
Lysogenic
What happens during the lysogenic gene expression step of the lysogenic life cycle?
The phage expresses an early gene repressor protein to block the lytic cycle and expresses integrase
What happens during the integration step of the lysogenic life cycle?
The viral DNA is integrated into the host genome through site specific recombination
What does integrase do?
Catalyzes site specific recombination between attP and attB sites to integrate the phage DNA into the genome
Does the bacterial genome have an attB or an attP site?
attB
Does the phage genome have an attB or an attP site?
attP
Why doesn’t the bacterial chromosome break when the phage becomes integrated?
The phage DNA is also circular. If it was linear it would break the chromosome
What happens during the host cell replication step of the lysogenic life cycle?
The bacterial cells replicate as per usual, and it also replicates the phage DNA and it gets passed onto the daughter cells
What happens during the induction step of the lysogenic life cycle?
The prophage cuts itself out of the genome and undergoes the lytic cycle
How does the prophage know when to cut itself out of the genome?
λ recognizes complexes of RecA and single stranded DNA that results from DNA damage, which causes the early gene repressor protein to be degraded
