Lecture 2 - bacteriophage lambda Flashcards
What are bacteriophages?
they are viruses that infect bacteria
What is lambda?
a phage (virus) that infects E. Coli
What is a virion?
The complete infectious form of a virus
What three things happen in the lytic cycle?
the phage replicates its genome, assembles many new phages, and then lyses the cell to release the new phages
What happens in the lysogenic cycle?
the phage integrates its genome into the host chromosome
What is a prophage?
the integrated phage DNA is called a prophage
What do virulent phages undergo?
a lytic cycle
What do temperate phages undergo?
both lytic and lysogenic life cycles
What are lysogenic genes?
codes for proteins that are needed for recombination
What are lytic genes?
codes for proteins that are needed to make new phages, lyse the host cell
What happens in the immediate early gene expression of the lytic cycle?
Pr and PL promoters express the genes N and cro only
In the middle stage of gene expression of the lytic cycle, what occurs?
N-mediated transcription antitermination allows expression of the Middle genes, which includes the transcription antitermination Q
In the late gene expression stage of the lytic cycle, what occurs?
Q-mediated transcription antitermination allows expression of the Late genes from the Pr’ promoter, including the proteins needed to assemble new phages and to lyse the host cell
What is cl?
the lambda repressor
What is the function of cl?
to chut off all other lambda genes except itself
What is required to establish and maintain lysogeny?
cl
What occurs in immediate early gene expression during the lysogenic cycle?
Pr and PL promoters express the genes N and cro only
*the same as the lytic stage
What occurs in the middle gene expression stage during the lysogenic cycle?
- the time needed to synthesize N delays expression of the other genes in the early gene operons
*cll is important for lysogeny - the antitermination by N causes the expression of cll
What is cll?
*it controls expression of cl (the lambda repressor)
What two promoters control the expression of cl?
Pre and Prm
What does the promoter Pre used for?
Pre is used to express cl when establishing lysogeny
What does the promoter Prm used for?
Prm is used to express cl when maintaining lysogeny
Since Pre is not active on its own, what must it be activated by?
cll (recall that cll is one of the middle genes)
How does cl function as a gene regulator?
cl binds to operator sequences called Or and OL but also represses transcription from Pr and Pl
When you shut off Pr, what does that mean for the production of cll?
the cll production will not be produced anymore
The activation of what promoter also makes mRNA for cl?
Prm
What controls whether the lytic or lysogenic cycle occurs?
a genetic switch
What does clll do?
it inhibits a cellular protease that degrades cll
What is Cro and what does it bind to?
Cro is a DNA binding protein that can also bind to Or and Ol but with opposite affinities relative to cl
* Cro binds to Or3 and ahuts off Prm
What happens if cl wins the race? Same with cro?
*if cl wins, the lysogenic cycle will be established
* if cro wins, the lytic cycle will be established
What is the connection between DNA damage and lysogen induction?
RecA protein
What is RecA?
a protein that plays a crucial role in the maintenance and repair of DNA
What is the second function of RecA?
RecA is also a protease that can cleave cl
When does RecA expression increase?
when there is DNA damage
