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Phosphates are molecules with the chemical formula PO4-. The presence of a negative charge causes phosphates to act as a nucleophile; it seeks a positive charge, therefore it is always found bound to other atoms or molecules. In organic systems, the phosphate molecule is the form that bodily phosphorus is used mainly in the form of nucleic acids DNA and RNA and the nucleotides that form them.


In DNA and RNA phosphates are used to build the phosphate-sugar backbone, which fixes the nucleotide bases in place. This is achieved by the formation of a phosphodiester bond, in which the phosphate molecule reacts with a hydroxyl group on the ribose sugar forming a bond and releasing water as a byproduct. Without the phosphate attached, the molecule consisting of just the base and the ribose sugar or deoxyribose sugar is called a nucleoside as opposed to a nucleotide[1].


The nucleotides most notably ATP and GTP are all triphosphate molecules which are highly efficient at releasing energy. This is because of the three phosphate molecules bound closely together on the ATP or GTP molecule, the negative charges on each phosphate exhibit repulsive forces between each other, so they can be hydrolysed in order to overcome these repulsive forces, and energy is released from phosphoanhydride bond hydrolysis.

ATP _> ADP + Pi (Pi is an inorganic phosphate)

GTP _> GDP + Pi

These high energy phosphoanhydride bonds, on average, have a ΔG of -30.5 kJ/mol[2]. Thus, the energy released from these bonds will be used for a cellular interaction such as a conformation shape change in a protein in skeletal muscle contraction[3].

It is possible to recycle the ADP and inorganic phosphate using the respiration, where glucose sugars are broken down to produce energy to reform the phosphodiester bond between ADP and Pi, recycling the molecules and forming ATP to be used again as an intermediate for energy release.


  1. Hartl D. L and Ruvolo M. (2012) Genetics, Analysis of Genes and Genomes, Eighth Edition, Burlington, Jones and Bartlett Learning
  2. ATP/ADP [Internet]. Chemistry LibreTexts. 2018 [cited 6 December 2018]. Available from:
  3. Biochemistry, sixth edition, Berg, Tymoczko and Stryer
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