DNA replication

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DNA replication is a duplication process where exact copies of DNA within cells are replicated, with very low error rate. They typically occur at a rate of 1 in 109 bases per replication. In Mitosis, DNA replication occurs during the S phase. DNA must be duplicated before the division takes place to main the chromosomal number of the two daughter cells. At the end of the division, two genetically identical daughter cells are formed. DNA replication is called Semi-conservative replication.

Within DNA replication the two strands are replicated in slightly different ways. The leading strand, the strand that runs 5' to 3', is replicated continuously. This is because it is known that the DNA polymerase is only able to synthesize in the 5' to 3' direction so the leading strand is in the correct orientation for the DNA polymerase so it can be replicated continuously. On the other hand, the lagging strand runs from 3' to 5' prime which means that it cannot be replicated continuously because the DNA polymerase can't replicate in that direction. This means that the lagging strand is replicated in fragments, which are given the name Okazaki fragments. The DNA is able to form loops so that the DNA polymerase can synthesize the new strand of DNA in the 5' to 3' direction. Other enzymes are then used to join up the gaps that are created through the replication in fragments[1].

Bacterial enzymes

Unlike DNA replication in Eukaryotes (e.g. animals), Bacteria have a limited set of key enzymes associated with this process. These are enumerated below, according to their supposed chronological order during replication in E. coli.

Here are two YouTube Video's which depict what occurs in DNA replication in bacteria. It highlights some of the enzymes listed above and there function in DNA replication. The first one shows an animation of DNA replication and the other shows replication fork coupling which displays DNA ability to form loops.

  1. https://www.youtube.com/watch?v=0Ha9nppnwOc
  2. https://www.youtube.com/watch?v=QMX7IpME7X8


  1. Burg J M, Tymoczko J L, Gatto, Jr G J, Stryer L. Biochemistry Eighth Edition. 2015. W.H. Freeman and Company. New York. Pg 831
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Cooper, G. M. (2000). The Cell: Molecular Approach. 2nd Edition. Washington, D.C: ASM Press.
  3. Messer, W., Blaesing, F., Majka, J., Nardmann, J., Schaper, S., Schmidt, A., Seitz, H., Speck, C., Tüngler, D., Wegrzyn, G., Weigel, C., Welzeck, M., Zakrzewska-Czerwinska, J.,(1999). Functional domains of DnaA proteins. Available at: http://www.sciencedirect.com/science/article/pii/S0300908499002151 (last assessed on 29/11/12).
  4. Benkovic, S. J, Valentine, A. M., and Salinas, F. (2001). Replisome-mediated DNA replication.
  5. Berg, M. J., Tymoczko, J. L., and Stryer, L. (2002). Biochemistry. 2nd Edition. New York: Freeman and Co.
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