Phosphorylation can be defined as a biochemical process in which a phosphate molecule is added to some organic compound, such as glucose and adenosine diphosphate (ADP).

Inside the cell, the most common type of phosphorylation is the formation of ATP by the addition of phosphate group to ADP.

There are 3 Types of Phosphorylation occurring in a cell

Substrate level phosphorylation

A metabolism reaction that results in the production of ATP or GTP by the transfer of a phosphate group from a substrate directly to ADP or GDP.

Oxidative phosphorylation during cellular respiration

Oxidative phosphorylation (OXPHOS) is defined as an electron transport chain driven phosphorylation by substrate oxidation coupled ATP synthesis through an electrochemical transmembrane gradient.

Difference between Substrate level phosphorylation, Oxidative phosphorylation and Photophosphorylation
Photo phosphorylation in Photosynthesis

The phosphorylation of ADP to form ATP using the energy of sunlight during photosynthesis is called photophosphorylation.

Let’s have a comparison of these 3 types.


Substrate level Phosphorylation

Oxidative Phosphorylation


Source of Phosphate

Organic molecule

Inorganic phosphate PO43-


Inorganic phosphate


Energy Source


High energy phosphate bond of donor

Proton motive force


Proton motive force

Location in Eukaryotes


Cytosol and mitochondrial matrix

Inner membrane of mitochondrion


Thylakoid of chloroplast


Location in Prokaryotes


Cytoplasmic membrane

Thylakoid on chromatophores


Oxygen not involved.

Oxygen as terminal electron acceptor

Oxygen evolved by photolysis of water.

Metabolic pathway

Common in many metabolic pathways like glycolysis, TCA cycle etc

Cellular respiration



Not involved

Not involved

Involved as two photosystems PSI and PSII

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