Lecture 12 Flashcards
(7 cards)
What is a virulent (lytic) bacteriophage?
A virulent bacteriophage always lyses and kills the host cell after infection.
What is a temperate bacteriophage?
A temperate bacteriophage can establish a long-term, stable relationship with the host cell (lysogeny), but is also capable of converting to a virulent (lytic) pathway.
What is the advantage of a bacteriophage being able to switch between lysogenic and lytic lifestyles?
The ability to switch between lysogenic and lytic lifestyles provides a survival advantage to the phage in different environmental conditions.
What ecological conditions would favor the lysogenic pathway over the lytic pathway?
Lysogeny is favored when the environment is unstable and there aren’t many hosts available.
Describe how the lambda repressor (cI) and Cro protein regulate the lytic and lysogenic pathways.
Immediately following the entry of the lambda genome into the cell, there is a race between cI and Cro to establish control of the lambda switch. cI has the highest affinity for the operator OR1, while Cro has the highest affinity for OR3. If Cro is made first, it will bind to OR3, block PRM, and the phage will enter the lytic pathway. If cI is made first, it binds to OR1, blocks PR, and the phage will enter the lysogenic pathway.
How does the lambda phage replicate during the lytic cycle?
During the lytic cycle, Cro protein promotes rightward transcription, leading to the expression of genes necessary for genome replication, phage particle assembly, and host cell lysis. The lambda genome enters into rolling circle replication to produce multiple copies of the viral DNA.
What is specialized transduction?
Phages that integrate into the host genome can sometimes take neighboring bits of host DNA with them when they excise. This process, called specialized transduction, is a mechanism of horizontal gene transfer.
