Phosphate backbone

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A phosphate backbone is the fixed, structural feature from which nucleic acids protrude in DNA and RNA[1]. This is formed by the repeating sequence of a phosphate group and deoxyribose, connected in sequence by phosphodiester bonds. The phosphate group always sticks out of the double helix of DNA due to the arrangement of the bases within the helix, and because phosphate groups are found throughout the entire DNA molecule, sticking outside the helix, it is referred to as a 'phosphate backbone' (imagine the bones that protrude through the skin along your spine). The sugar-phosphate backbone is negatively charged due to the presence of the phosphate groups hence making it also hydrophilic.

The sugar-phosphate backbone determines the directionality of the molecule, the sugar being at the 3' end and the phosphate at the 5' end of each nucleotide[2].


  1. Berg.J, Tymoczko.J,Styer.L (2012)Biochemistry, 7th edition, New York: W.H. Freemann (Page 4)
  2. Vikram Savkar, Phosphate Backbone, Nature Education, [Online] Available:
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