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DNA replication




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DNA replication. The double helix is unwound and each strand acts as a template. Bases are matched to synthesize the new partner strands.

DNA replication is the process of copying a double-stranded DNA molecule. Both strands serve as templates for the reproduction of the opposite strand. This process occurs in all life forms with DNA.[1] There are some differences in the control of DNA replication in prokaryotic and eukaryotic organisms.

In a cell, DNA replication begins at specific places in the genome, called origins.[2] As the DNA unwinds at the origin, the synthesis of new strands forms at a replication fork. In addition to DNA polymerase,[3] other enzymes at the fork help to start and continue the DNA synthesis.

DNA polymerase

DNA polymerases are a family of enzymes that carry out all forms of DNA replication.[4] However, a DNA polymerase can only extend an existing DNA strand paired with a template strand; it cannot begin the synthesis of a new strand. To begin synthesis, a short fragment of DNA or RNA, called a 'primer', is created and paired with the template DNA strand.

Many enzymes are involved in the DNA replication fork.

In general, DNA polymerases are extremely accurate, making less than one mistake for every 107 (10 million) nucleotides added.[5] Even so, some DNA polymerases also have 'proofreading' ability: they can remove nucleotides from the end of a strand in order to correct mismatched bases.

DNA repair

DNA in cells is constantly being damaged.[6] The nucleus of cells contains a number of repair mechanisms which fix almost all of this damage. "A large set of DNA repair enzymes continuously scan the DNA and repair any damaged nucleotides.[7]

References

  1. ↑ Most viruses use RNA instead.
  2. ↑ Berg J.M. et al (2002). Biochemistry. W.H. Freeman. ISBN 0-7167-3051-0 .Chapter 27, Section 4: DNA Replication of both strands proceeds rapidly from specific start sites
  3. ↑ The enzyme which synthesizes new DNA by adding nucleotides matched to the template strand.
  4. ↑ Berg J.M. et al (2002). Biochemistry. W.H. Freeman. ISBN 0-7167-3051-0 . Chapter 27, Section 2: DNA Polymerases require a template and a primer
  5. ↑ McCulloch S.D. & Kunkel T.A (2008). "The fidelity of DNA synthesis by eukaryotic replicative and translesion synthesis polymerases". Cell Research 18 (1): 148–61. doi:10.1038/cr.2008.4 . PMID 18166979 .
  6. ↑ Causes include reactive molecules, chemicals and radiation from the environment, and damage caused by heat.
  7. ↑ Alberts B et al 2002. Molecular biology of the cell. 4th ed, Garland. p275. ISBN 0-8153-3218-1

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