DNA polymerase

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DNA polymerase is involved in the process of DNA replication by using a DNA template as a guide for joining nucleotides together. There are different types,some are named below:

  1. DNA Polymerase I - Removes primers and assemble DNA
  2. DNA Polymerase II - Responsible for repair
  3. DNA Polymerase III - The main replicative enzyme

DNA polymerase 3 is thought to be the most important one and is involved in DNA elongation. It is fast (1000 bases per second), processive (1000-5000 bases added before polymerase falls off DNA), accurate and works in the 5' to 3' direction.

DNA polymerase 1 has proof-reading activity. It is slow and non-processive and only adds a few bases to the chain. It also removes RNA primers.

DNA polymerase I has two exonuclease activities and it performs these by working along the strand in two different directions. The proof-reading activity of DNA polymerase I is only carried out in the 3' - 5' direction, whereas in the opposite direction (5' - 3') the function is to remove RNA primers. When proof-reading, a mismatched base is identified which means another nucelotide cannot be added on to the growing chain. The wrong base is then removed and the correct one added so the polymerase can continue to work along the strand adding more bases to carry out the process of DNA replication. In 1957, the first DNA polymerase was discovered [1].


  1. Bruce Alberts et al.2008. Molecular Biology of a cell. 5th edition(5:226)
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