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Dideoxynucleotides triphosphates (DdNTP) are chain terminating nucleotide bases of DNA that, once added to a nucleotide sequence, inhibits DNA polymerase action[1] and include the bases ddATP, ddTTP, ddGTP and ddCTP. Their structure is that of a Deoxynucleotide (dNTP); a triphosphate and base group bound to the 4' and 1' of a pentose sugar (respectively), with the 3'-hydroxyl group replaced by a hydrogen molecule. The 3'-hydroxyl is essential for chain Elongation, and without it, DNA polymerase cannot add further dNTPs beacuse the Phosphodiester bond used to them is formed through a Condensation reaction[2]. DdNTPs are used with PCR and gel electrophoresis in Sanger style DNA sequencing[3]


  1. Lefers, M. (2004). dideoxynucleotides. [Online] Available: http://groups.molbiosci.northwestern.edu/holmgren/Glossary/Definitions/Def-D/dideoxynucleotide.html. [Accessed 24 November 2013].
  2. Canfield, E. (1999). Sanger Method for DNA Sequencing. [Online] Availible: http://www.bio.davidson.edu/Bio111/seq.html [Accessed 24 November 2013].
  3. Sanger, F. Nicklen, S. Coulson, AR. (1977) DNA sequencing with chain-terminating inhibitors. [Online] PubMed. Availible: http://www.ncbi.nlm.nih.gov/pubmed/271968 [Accessed 24 November 2013].
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