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Phosphorylation is a biochemical reaction where a phosphate group (PO4) is covalently bonded to another organic molecule. An example of phosphorylation is the addition of a phosphate to Adenosine Diphosphate (ADP) to form the molecule Adenosine Triphosphate (ATP)[1]. Enzymes called phosphotransferase or kinases catalyze the transfer action of phosphoryl group to an organic molecule[2]. Oxidative phosphorylation is the chemical pathway in which ATP is synthesised in mitochondria and bacteria. This is driven by the transfer of electrons across an electron transfer chain[3].

Phosphorylation occurs in all domains of life. Its basic function is to switch compounds from one state to another, and back again.

An example of phosphorylation is the conversion of glucose to glucose monophosphate, which is a key initial stage of glycolysis.

Phosphorylation can also occur by activation of protein kinases. They add a phosphate group to proteins which regulate cell activity.


  2. Definition of Phosphorylation [Internet]. MedicineNet. 2018 [cited 23 October 2018]. Available from:
  3. Molecular Biology of the Cell, 5th Edition, Garland Sciences, Alberts et al, Pg 819-821 and Glossary 27.

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