Chromosome Replication in E. coli
Occurs via binary fission* - chromosome replication triggers initiation of cell division.
- We illustrate this in Escherichia coli; be aware that not all bacteria replicate in this exact manner.
Chromosome Replication in E. coli
Bacterial chromosome replication in E. coli occurs via binary fission - chromosome replication triggers initiation of cell division.
We illustrate this in Escherichia coli; be aware that not all bacteria replicate in this exact manner.
First drawing
Single circular chromosome with inner and outer strands.
In reality, bacterial DNA is arranged in loops. Recall that there is no distinct nucleus, as in eukaryotic cells; instead, DNA lies in the nucleoid region.
Origin of replication is marked by oriC; this is where the replication initiator proteins bind.
Terminus is located opposite oriC; this is the region where DNA replication terminates.
Second drawing
After DNA replication begins:
Outer and inner parental strands begin to separate in bidirectional replication.
The replication "bubble" is the space between the strands.
Two y-shaped replication forks form, one on each side of the bubble.
DNA helicases separate the parental DNA strands in short segments, thus creating the replication forks; if the two strands separated all at once, excessive DNA damage could occur.
Developing daughter strands: each one begins at the origin of its parental strand and grows towards its terminal end.
These complementary daughter strands are synthesized by the
replisome, which comprises DNA polymerase III and other components.
Third drawing
The parental and growing daughter strands are further along in the replication process.
The parental strands have further separated from each other as the daughter strands grow towards the terminal region.
Fourth drawing
Finally, the chromosomes separate after the daughter strands are complete.
DNA replication is semiconservative:
Each new chromosome comprises one strand of DNA from the parental chromosome and one complementary daughter strand.
