Bacterial Cell Cycle and ColE1 Flashcards
how is septum formation associated with doubling time of bacteria?
- a septum is the division in the middle of the mother cell to get a separation and formation of the two resultant daughter cells
- it will always take 20 minutes to form the septum and split the cell into 2
What are the values (minutes) of C and D, and what do C and D stand for?
- It requires 40 minutes to replicate the bacterial chromosome (at normal temperature) known as C
- Completion of replication cycle triggers a bacterial division 20 minutes later known as D
- C+D=60 minutes; this is the total time between the initiation of DNA replication and cell division
- The doubling time of e. Coli can vary over a 10x range, depending on growth conditions
What is a unit cell?
an entity 1.7 micrometers long; one origin per unit cell.
What is the significance of 1.7 microns in terms of the number of origins present in E. coli?
- A rapidly growing cell with two origins will be 1.7-3.4 micrometers long
- At 10 minutes after division, the cell mass increases sufficiently to support an initiation at both origins
- 1.7 microns is used to Measure its length to see if its replicating
- Up to 1.7 microns long - then there is only one origin working - longer than this, it started replication for the daughter cells
- Anything between that will have 2 origins going at the same time
- Keep doubling to see how many origins there will be
How could you experimentally change the copy number of the ColE1 plasmid?
- Change the activity level of the promoter you can alter the copy number
- Not making as much of a negative regulator so it takes longer to shut down replication
- End up with a higher copy number
- Made the promoter that makes the primer strong, you can also increase the final copy number through this mechanism as well
how does rna 1 negative regulator “count” the copy number?
- P-1 promoter regulates the expression level (abundance) of RNA 1 regulatory transcript
- Alter the promoter, alter the copy number
How does the cell know when to initiate the replication cycle?
- Rapidly growing cells are larger and posses a greater number of origins (multi forked chromosomes)
- Initiation occurs at a constant ratio of cell mass to the number of chromosome origins
How is cell mass titrated?
there are two competing models: the current and alternative model
current model for mass titration
Current model suggests that initiation is controlled by the accumulation of a positive acting factor. Accumulation of a critical amount would trigger initiation (this factor is dilute in newly divided cells). DNA A protein is likely the candidate
alternative model for mass titration
Alternative model suggests that initiation is controlled by the accumulation of a negative acting factor (an inhibitor) inhibitor may be synthesized to a fixed level (no initiation) and diluted below at an effective level in larger cells (initiation)
How many replication origins are active in an e. Coli cell that is 2.1 micrometers in size?
2
Xer
- Site specific recombination system to resolve a dimeric genome into monomer genomes after replication
- Enzyme that makes the cut that resolves the two genomes
- Resolvase
Dif
location where Xer makes the cut
how fast does the replication fork move in bacterial replication in the cell cycle?
50,000 bp/min
multifork chromosome
- Fast rate of growth
- The new strands have an active origin and another pair of replication fork forms