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[[DNA|DNA]] replication is a duplication process where exact copies of [[DNA]]&nbsp;within [[Cells|cells]] are replicated, with very low error rate. They typically occur at a rate of 1 in 10<sup>9</sup><sup></sup><sup></sup> bases per replication. In [[Mitosis]], DNA replication occurs during the [[S phase|S phase]]. DNA must be&nbsp;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.&nbsp;DNA replication is [[semi-conservative]].  
[[DNA|DNA]] replication is a duplication process where exact copies of [[DNA]]&nbsp;within [[Cells|cells]] are replicated, with very low error rate. They typically occur at a rate of 1 in 10<sup>9</sup><sup></sup><sup></sup> bases per replication. In [[Mitosis]], DNA replication occurs during the [[S phase|S phase]]. DNA must be&nbsp;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.&nbsp;DNA replication is [[Semi-conservative]].  


== Bacterial enzymes<br> ==
== Bacterial enzymes<br> ==
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Unlike DNA replication in [[Eukaryotes]](e.g. animals), [[Bacteria]]&nbsp;have a limited set of key enzymes associated with this process. These are enumerated below,&nbsp;according to their supposed chronological order during replication in [[E. coli]].  
Unlike DNA replication in [[Eukaryotes]](e.g. animals), [[Bacteria]]&nbsp;have a limited set of key enzymes associated with this process. These are enumerated below,&nbsp;according to their supposed chronological order during replication in [[E. coli]].  


*[[Type I topoisomerase]] - Catalyses a reversible&nbsp;formation of a nick on 1 antiparallel DNA strand. This breakage is at a single point on DNA [[Phosphate backbone]], allowing the dsDNA to unravel<ref name="Topoisomerase">Cooper, G. M. (2000). The Cell: Molecular Approach. 2nd Edition. Washington, D.C: ASM Press.</ref>.  
*[[Type I topoisomerase]] - Catalyses a reversible&nbsp;formation of a nick on 1 antiparallel DNA strand. This breakage is at a single point on DNA [[phosphate backbone]], allowing the dsDNA to unravel<ref name="Topoisomerase">Cooper, G. M. (2000). The Cell: Molecular Approach. 2nd Edition. Washington, D.C: ASM Press.</ref>.  
*[[Dna A]] - Intiates DNA replication by [[OriC]] recognition on bacterial DNA. In addition, it&nbsp;instigates DNA&nbsp;helicase double strand unzipping<ref name="Dna A">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).</ref>.  
*[[Dna A]] - Intiates DNA replication by [[OriC]] recognition on bacterial DNA. In addition, it&nbsp;instigates DNA&nbsp;helicase double strand unzipping<ref name="Dna A">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).</ref>.  
*[[DNA helicase|DNA Helicase]] - Unzips double stranded DNA by breaking [[Hydrogen bonds|hydrogen bonds]] between base pairs, to allow other enzymes to access bases<ref name="Topoisomerase" />.  
*[[DNA helicase|DNA Helicase]] - Unzips double stranded DNA by breaking [[Hydrogen bonds|hydrogen bonds]] between base pairs, to allow other enzymes to access bases<ref name="Topoisomerase" />.  
*[[SSB protein]] - protein that stops unravelled DNA from reforming into a double strand<ref name="SSB protein">Benkovic, S. J, Valentine, A. M., and Salinas, F. (2001). Replisome-mediated DNA replication. Available at: http://www.annualreviews.org/doi/full/10.1146/annurev.biochem.70.1.181?prevSearch=THE%2BDNA%2BREPLICATION%2BFORK%2BIN%2BPROKARYOTIC%2BCELLS&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;searchHistoryKey= (last assessed on 29/11/12).</ref>  
*[[SSB protein]] - protein that stops unravelled DNA from reforming into a double strand<ref name="SSB protein">Benkovic, S. J, Valentine, A. M., and Salinas, F. (2001). Replisome-mediated DNA replication. Available at: http://www.annualreviews.org/doi/full/10.1146/annurev.biochem.70.1.181?prevSearch=THE%2BDNA%2BREPLICATION%2BFORK%2BIN%2BPROKARYOTIC%2BCELLS&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;searchHistoryKey= (last assessed on 29/11/12).</ref>  
*[[DNA Primase|Primase]] - Catalyses the polymerisation of short [[RNA|RNA]] strands (primers) which&nbsp;promote [[DNA polymerase III|DNA polymerase III]] to bind and initiate the replication. Note, this enzyme is functionally an [[RNA polymerase]]<ref name="Topoisomerase" />.  
*[[DNA Primase|Primase]] - Catalyses the polymerisation of short [[RNA|RNA]] strands (primers) which&nbsp;promote [[DNA polymerase III|DNA polymerase III]] to bind and initiate the replication. Note, this enzyme is functionally an [[RNA polymerase]]<ref name="Topoisomerase" />.  
*[[DNA Polymerase|DNA Polymerase III]] - Catalyses the addition of nucleotides ([[DNTPs]]) onto both DNA&nbsp;strands (i.e. leader and lagging). Addition is strictly in 5 '- 3' direction.  
*[[DNA Polymerase|DNA Polymerase III]] - Catalyses the addition of nucleotides ([[DNTPs]]) onto both DNA&nbsp;strands (i.e. leader and lagging). Addition is strictly in 5 '- 3' direction.  
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*[[DNA polymerase I|DNA Polymerase I]] - Catalyses&nbsp;the addition of short DNA&nbsp;fragments in place of&nbsp;now degraded [[Javascript:void(0);/*1354234678397*/|RNA&nbsp;primers]]; also got a&nbsp;proofreading via [[3' to 5' exonuclease]] activity (reduces the error rate<ref name="Topoisomerase" />)
*[[DNA polymerase I|DNA Polymerase I]] - Catalyses&nbsp;the addition of short DNA&nbsp;fragments in place of&nbsp;now degraded [[Javascript:void(0);/*1354234678397*/|RNA&nbsp;primers]]; also got a&nbsp;proofreading via [[3' to 5' exonuclease]] activity (reduces the error rate<ref name="Topoisomerase" />)


*[[Dna ligase|DNA Ligase]] - Joins&nbsp;[[Phosphate backbone]]at&nbsp;the&nbsp;lagging strand (Okazaki fragments<ref name="Topoisomerase" />)  
*[[Dna ligase|DNA Ligase]] - Joins&nbsp;[[phosphate backbone]]&nbsp;at&nbsp;the&nbsp;lagging strand (Okazaki fragments<ref name="Topoisomerase" />)  
*[[Type II topoisomerase]] - Catalyses a reversible formation of a nick on 2 antiparallel DNA strands (at the same position on each). This allows produced circular DNA to escape from parental (segregation).&nbsp; Once again, nicks form at [[Phosphate backbones]]<ref name="Topoisomerase" />.  
*[[Type II topoisomerase]] - Catalyses a reversible formation of a nick on 2 antiparallel DNA strands (at the same position on each). This allows produced circular DNA to escape from parental (segregation).&nbsp; Once again, nicks form at [[phosphate backbones]]<ref name="Topoisomerase" />.  
*[[DNA Polymerase II]] - Involved in DNA repair (e.g. during dimerisation of thymine bases via mutagens of radiation<ref>Berg, M. J., Tymoczko, J. L., and Stryer, L. (2002). Biochemistry. 2nd Edition. New York: Freeman and Co.</ref>)
*[[DNA Polymerase II]] - Involved in DNA repair (e.g. during dimerisation of thymine bases via mutagens of radiation<ref>Berg, M. J., Tymoczko, J. L., and Stryer, L. (2002). Biochemistry. 2nd Edition. New York: Freeman and Co.</ref>)


Revision as of 01:47, 30 November 2012

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 Semi-conservative.

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.

  • Type I topoisomerase - Catalyses a reversible formation of a nick on 1 antiparallel DNA strand. This breakage is at a single point on DNA phosphate backbone, allowing the dsDNA to unravel[1].
  • Dna A - Intiates DNA replication by OriC recognition on bacterial DNA. In addition, it instigates DNA helicase double strand unzipping[2].
  • DNA Helicase - Unzips double stranded DNA by breaking hydrogen bonds between base pairs, to allow other enzymes to access bases[1].
  • SSB protein - protein that stops unravelled DNA from reforming into a double strand[3]
  • Primase - Catalyses the polymerisation of short RNA strands (primers) which promote DNA polymerase III to bind and initiate the replication. Note, this enzyme is functionally an RNA polymerase[1].
  • DNA Polymerase III - Catalyses the addition of nucleotides (DNTPs) onto both DNA strands (i.e. leader and lagging). Addition is strictly in 5 '- 3' direction.
  • RNase H - Catalyses degradation of RNA primers (DNA and RNA hybrids[1])
  • DNA Polymerase I - Catalyses the addition of short DNA fragments in place of now degraded RNA primers; also got a proofreading via 3' to 5' exonuclease activity (reduces the error rate[1])

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Cooper, G. M. (2000). The Cell: Molecular Approach. 2nd Edition. Washington, D.C: ASM Press.
  2. ↑ 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).
  3. ↑ Benkovic, S. J, Valentine, A. M., and Salinas, F. (2001). Replisome-mediated DNA replication. Available at: http://www.annualreviews.org/doi/full/10.1146/annurev.biochem.70.1.181?prevSearch=THE%2BDNA%2BREPLICATION%2BFORK%2BIN%2BPROKARYOTIC%2BCELLS&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;searchHistoryKey= (last assessed on 29/11/12).
  4. ↑ Berg, M. J., Tymoczko, J. L., and Stryer, L. (2002). Biochemistry. 2nd Edition. New York: Freeman and Co.


 

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