Green 17 - Bacterial Cell Division

Question 1

Describe what happens in the eclipse stage of the initiation of DNA replication.

Answer 1

SeqA inhibits the action of DnaA no DNA replication in this stage levels of DnaA ATP initially falls but then starts to rise again old DnaA ATP -> new DnaA ADP

Question 2

What needs to occur with regards to numbers of DnaA for the initiation of a new round of replication to take place and for the cell to divide?

Answer 2

Ratio of 1 needs to be reached between TOTAL amounts of DnaA ATP:ADP in the cell

Question 3

Describe the initiation of replication @ the oriC

Answer 3

DnaAATP and ADP compete for binding @ OriC DnaAATP recruits components of the membrane bound replisome (helicase and loader) once helicase has separated the strands, DNAP is recruited and replication starts

Question 4

Describe the 3 theories that have been suggested to describe DNA replication.

Answer 4

• sizer = once the cell has reached a certain size, this triggers division - timer = at a specific time through a cell’s life cycle division occurs, irrespective of size - adder = a constant weight / size added on to the birth weight per generation & then the cell divides (chosen theory)

Question 5

Describe the composition and placement of the E. coli divisome.

Answer 5

Divisome placed in the mid cell Contains many proteins on both periplasmic and cytoplasmic faces FtsZ (cytoplasm) involved in formation of the ring and pinching off of said ring FtsK (membrane) involved in chromosome segregation All together - divisome involved in septum remodelling, septum constriction and chromosome segregation

Question 6

Give one example of a + and - regulation of selecting the division site for E. coli.

Answer 6

• Min = depolymerises @ mid cell. polymerises from pole. allows FtsZ formation @ mid cell

SlmA = surrounds nucleoid therefore doesnt allow FtsZ ring formation in the middle when nucleoid is not at a pole

+ FtsK = DNA translocase FtsK moves chromosomes to either pole during later stages of division

Ter linkage = FtsZ linked to terminator regions of chromosomes (last stage of replication). therefore FtsZ knows where the chromosomes will finish replicating and division will occur here

Question 7

Use a diagram to explain endospore formation

Answer 7