DNA is the genetic material of the cell, which has to be distributed to the daughter cells. Hence the entire DNA molecule should be replicated before the cell division. Hence, DNA replication is an important process which takes place in every organisms, be it prokaryotic or eukaryotic. The DNA replication process produces two identical copies of daughter DNA molecules using the existing DNA molecule as template. Replication process in eukaryotic and prokaryotic organisms share a lot similarity with few differences.
We have already uploaded posts on prokaryotic and eukaryotic replication (in two parts; first one on Initiation and second one on Elongation & termination). In this post, we shall see the differences between the prokaryotic and eukaryotic DNA replication.
(Just for info: Also read our post on Transcription in Prokaryotes.)
The differences between prokaryotic and eukaryotic replication mostly arise due to the dissimilarities in the size and the complexity of their genome. The eukaryotic cell has much more DNA content than the prokaryotic cell, which densely packed in the nucleus of the eukaryotic cell as a chromosome. For e.g. the human genome is roughly around 1000 times larger than the E. coli genome.
(Just for info: Also read our post on Chromosome Banding)
The prokaryotic cells have closed circular genome of about 0.6-1.0 Mb in size, within the nucleoid. Prokaryotic cell may even have one or more circular plasmid species of around 2 kb -1.7 Mb. The eukaryotic genome on other hand is linear and condensed into one or more chromosomes. For instance, the human genome which contains around 2.9 billion base pairs are arranged in a pair of 23 chromosmes.
The following are few differences between the prokaryotic and the eukaryotic replication:
1. The prokaryotic replication occurs in the cytoplasm whereas the eukaryotic replication occurs in the nucleus.
2. The replication can take place in prokaryotes at any time, and is followed by the cell division. In eukaryotes, the replication takes place particularly, during the S phase of the cell cycle.
3. Prokaryotic genome has a single origin of replication, that is the site of replication Initiation. As the eukaryotic genome is large, it has multiple origins, to increase the speed of replication.
4. As there is only one Ori, the prokaryotic genome has a single expanding replication bubble. Whereas the eukaryotic genome have a multiple replication bubble to accelerate the speed of complete replication process.
5. The prokaryotic genome has a single termination site on the other side of Ori. In eukaryotes, the termination involves merging of two adjacent replication forks and replication of chromosome ends known as telomeres (see the steps in the previous post DNA Replication: Eukaryotic Elongation and Termination).
Fig 4: Synthesis of telomeric DNA repeats by Telomerase (Verhoeven et al, 2014).
6. DNA polymerases III is the major DNA polymerase involved in the prokaryotic replication.
Eukaryotic replication involves DNA polymerase alpha, delta and epsilon as the major polymerization enzymes. Eukaryotes also have DNA polymerase γ for mitochondrial DNA replication.
7. The replication of the prokaryotes proceeds at a much faster rate than the eukaryotes. Prokaryotic replication proceeds at the rate of about 2000 bp per second while in eukaryotes at around 100 nucleotides per second.
8. The replication is the two types of organisms also exists in the length of the Okazaki fragments. the Okazaki fragments In prokaryotes, around 1000-2000 nucleotides, are longer than that in the eukaryotes, around 100 and 200 nucleotides.
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Read other posts by The Biotech Notes:
Fijalkowska et al (2012) DNA replication fidelity in Escherichia coli: A multi-DNA polymerase affair. FEMS microbiology reviews. 36. 1105-21. 10.1111/j.1574-6976.2012.00338.x.
Boehm et al. (2016) The Many Roles of PCNA in Eukaryotic DNA Replication. Enzymes 39:231-54.
Verhoeven et al (2014). Cellular aging in depression: Permanent imprint or reversible process?: An overview of the current evidence, mechanistic pathways, and targets for interventions. BioEssays 36(10):968-78.