Impossible Bacterial Replication
Bacteria are believed to be the oldest domain of life and over billions of years, they have been able to optimize many vital processes. These diverse living things are well known for their extremely rapid growth rate at ideal conditions, which seems to go beyond the impossible. Escherichia coli, the most studied microorganism, is able to duplicate its population every 20 minutes at optimum conditions, but it should take around 40 minutes to replicate its entire chromosome once. How do these bacteria manage to go multiply at such a rate, without losing genetic information?
Replication of the genetic material should be the number-one constrain for cell duplication, but bacteria seem to defy this limit. As replication is the main objective of the cell cycle, chromosomal DNA needs to be prepared, replicated, and separated for mitosis, while still been used to create proteins and direct all cellular processes. Given that the E. coli circular genome is 4.64 million base pares long with a single origin of replication, and that the DNA polymerase replicates DNA at a rate of around a 1000 base pares per second, it would take a bacterial cell around 40 minutes just to replicate its genome once. Moreover, it is a biological principle that, after mitosis, each daughter cell must have the same amount of genetic material as the mother cell. So, how can bacteria defy this intrinsic limit and duplicate twice as fast as their replication rate?
These mesmerizing organisms have been found to set off a new replication cycle before a previous one has been ended. This means that when two bacterial cells separate, their chromosomes are already halfway through a new replication process. Thus, the replication constrain depends only on the time between the setting off of new replication cycles. It is important to take into account that bacteria have to be able to maintain all other vital pathways through the central dogma simultaneously. Once again, bacteria manage to solve intricate design problems that reflect the high optimization process that these organisms have undergone in the last three and a half billion years.
REFERENCES
- L. A. Moran. 2008. DNA replication in E. coli: solution. Sandwalk Blogspot. Extracted online on Oct. 25 2015.
- Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., Walter, P. 2008. Chapter 5: DNA Replication, Repair, and Recombination. Molecular Biology of the Cell. S. Masson, E. Jeffcock, M, Anderson, S. Granum, editors. Garland Science/New York, USA. 281–293
- University of California Santa Cruz Genome Browser. Escherichia Coli K-12 Genome. Extracted online on Oct. 25 2015