Unit 2: Replication connected to the Cell Cycle and Bacterial Replication Initiation Flashcards
Catenation
Circular bacterial chromosomes are linked rungs after being replicated. Must be seperated.
topoisomerases
Enzymes that cut entangled circular bacterial chromosomes after DNA replication.
Doubling time of E.Coli
Can have a 10-fold range. 18 to 180 minutes.
Requires 40 minutes to replicate the bacterial chromosome (at normal temp)
Depending on the doubling time, the replication cycle for next cycle can begin prior to cell division finishing resulting in multiforked chromosomes.
The frequency of initiation of cycles of replication is adjusted to fit the rate at which the cell is growing.
Two “links” between replication and cell growth
The frequency of initiation of cycles of replication is adjusted to fit the rate at which the cell is growing.
The completion of a replication cycle is connected with division of the cell.
9.3 The Shape and Spatial Organization of a Bacterium Are Important During Chromosome Segregation and Cell Division
Bacterial chromosomes are specifically arranged and positioned inside cells.
A rigid peptidoglycan cell wall surrounds the cell and gives it its shape.
The rod shape of E. coli is dependent on MreB, PBP2, and RodA.
Septum formation is initiated mid-cell, 50% of the distance from the septum to each end of the bacterium.
9.1 Introduction - Replication is Connected to the Cell Cycle
A major difference between prokaryotes and eukaryotes is the way in which replication is controlled and linked to the cell cycle.
Chromosomes reside in the nucleus.
Each chromosome consists of many units of replication called replicons.
Replication requires coordination of these replicons to reproduce DNA during a discrete period of the cell cycle.
The decision about whether to replicate is determined by a complex pathway that regulates the cell cycle.
Duplicated chromosomes are segregated to daughter cells during mitosis by means of a special apparatus.
9.2 Bacterial Replication Is Connected to the Cell Cycle
KEY CONCEPTS
The doubling time of Escherichia coli can vary over a range of up to 10 times, depending on growth conditions.
It requires 40 minutes to replicate the bacterial chromosome (at normal temperature).
Completion of a replication cycle triggers a bacterial division 20 minutes later.
If the doubling time is approximately 60 minutes, a replication cycle is initiated before the division resulting from the previous replication cycle.
Fast rates of growth therefore produce multiforked chromosomes.
9.3 The Shape and Spatial Organization of a Bacterium Are Important During Chromosome Segregation and Cell Division
KEY CONCEPTS
Bacterial chromosomes are specifically arranged and positioned inside cells.
A rigid peptidoglycan cell wall surrounds the cell and gives it its shape.
The rod shape of E. coli is dependent on MreB, PBP2, and RodA.
Septum formation is initiated mid-cell, 50% of the distance from the septum to each end of the bacterium.
nucleoid
The nucleoid is an irregularly shaped region within the prokaryotic cell that contains all or most of the genetic material.
The chromosome of a prokaryote is circular, and its length is very large compared to the cell dimensions, so it needs to be compacted in order to fit.
peptidoglycan
a substance forming the cell walls of many bacteria, consisting of disaccharide units interlinked with short peptides (via transglycosylation and transpeptidation)
proteins required to maintain rod-like shape of E.Coli
MreB - resembles actin in eukarytoes (actin polymerizes to form cytoskeletal filaments).
RodA - member of the SEDS (shape, elongation, division, sporulation) family present in all bacteria that have a peptidoglycan cell wall. Helps form peptidoglycan.
PBP2 - penicillin-binding protein 2 is the transpeptidase that interacts with RodA
RodA & PBP2 demonstrate the important principle that shape and rigidity can be determined by the simple extension of a polymeric structure.
Septum
A the middle of the dividing cell, an invagination forms from the surrounding envelope. The septum consists of the same components as the cell envelope.
Divides the two daughter cells entirely.
The end of the cell cycle in a bacterium is defined by the division of a mother cell into two daughter cells.
Septum becomes the new pole for each daughter cell.
9.4 Mutations in Division or Segregation Affect Cell Shape
KEY CONCEPTS
fts mutants form long filaments because the septum that divides the daughter bacteria fails to form.
Minicells form in mutants that produce too many septa; they are small and lack DNA.
Anucleate cells of normal size are generated by partition mutants, in which the duplicate chromosomes fail to separate.
9.5 FtsZ Is Necessary for Septum Formation
KEY CONCEPTS
The product of ftsZ is required for septum formation.
FtsZ is a GTPase that resembles tubulin, and polymerizes to form a ring on the inside of the bacterial envelope. It is required to recruit the enzymes needed to form the septum.
Z-ring
FtsZ functions at an early stage of septum formation. Early in the division cycle, FtsZ is localized throughout the cytoplasm, but prior to cell division FtsZ becomes localized in a ring around the circumference at the mid-cell position.
Rate limiting step in the formation of the septum.
