Lecture 2 - bacteriophage lambda

Question 1

What are bacteriophages?

Answer 1

they are viruses that infect bacteria

Question 2

What is lambda?

Answer 2

a phage (virus) that infects E. Coli

Question 3

What is a virion?

Answer 3

The complete infectious form of a virus

Question 4

What three things happen in the lytic cycle?

Answer 4

the phage replicates its genome, assembles many new phages, and then lyses the cell to release the new phages

Question 5

What happens in the lysogenic cycle?

Answer 5

the phage integrates its genome into the host chromosome

Question 6

What is a prophage?

Answer 6

the integrated phage DNA is called a prophage

Question 7

What do virulent phages undergo?

Answer 7

a lytic cycle

Question 8

What do temperate phages undergo?

Answer 8

both lytic and lysogenic life cycles

Question 9

What are lysogenic genes?

Answer 9

codes for proteins that are needed for recombination

Question 10

What are lytic genes?

Answer 10

codes for proteins that are needed to make new phages, lyse the host cell

Question 11

What happens in the immediate early gene expression of the lytic cycle?

Answer 11

Pr and PL promoters express the genes N and cro only

Question 12

In the middle stage of gene expression of the lytic cycle, what occurs?

Answer 12

N-mediated transcription antitermination allows expression of the Middle genes, which includes the transcription antitermination Q

Question 13

In the late gene expression stage of the lytic cycle, what occurs?

Answer 13

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

Question 14

What is cl?

Answer 14

the lambda repressor

Question 15

What is the function of cl?

Answer 15

to chut off all other lambda genes except itself

Question 16

What is required to establish and maintain lysogeny?

Answer 16

cl

Question 17

What occurs in immediate early gene expression during the lysogenic cycle?

Answer 17

Pr and PL promoters express the genes N and cro only
*the same as the lytic stage

Question 18

What occurs in the middle gene expression stage during the lysogenic cycle?

Answer 18

• 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

Question 19

What is cll?

Answer 19

*it controls expression of cl (the lambda repressor)

Question 20

What two promoters control the expression of cl?

Answer 20

Pre and Prm

Question 21

What does the promoter Pre used for?

Answer 21

Pre is used to express cl when establishing lysogeny

Question 22

What does the promoter Prm used for?

Answer 22

Prm is used to express cl when maintaining lysogeny

Question 23

Since Pre is not active on its own, what must it be activated by?

Answer 23

cll (recall that cll is one of the middle genes)

Question 24

How does cl function as a gene regulator?

Answer 24

cl binds to operator sequences called Or and OL but also represses transcription from Pr and Pl

Question 25

When you shut off Pr, what does that mean for the production of cll?

Answer 25

the cll production will not be produced anymore

Question 26

The activation of what promoter also makes mRNA for cl?

Answer 26

Prm

Question 27

What controls whether the lytic or lysogenic cycle occurs?

Answer 27

a genetic switch

Question 28

What does clll do?

Answer 28

it inhibits a cellular protease that degrades cll

Question 29

What is Cro and what does it bind to?

Answer 29

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

Question 30

What happens if cl wins the race? Same with cro?

Answer 30

*if cl wins, the lysogenic cycle will be established
* if cro wins, the lytic cycle will be established

Question 31

What is the connection between DNA damage and lysogen induction?

Answer 31

RecA protein

Question 32

What is RecA?

Answer 32

a protein that plays a crucial role in the maintenance and repair of DNA

Question 33

What is the second function of RecA?

Answer 33

RecA is also a protease that can cleave cl

Question 34

When does RecA expression increase?

Answer 34

when there is DNA damage