Phosphorylation Definition

Phosphorylation is the addition of a phosphoryl group (containing phosphate) to a molecule. For life science this is vitally important for the energy storage utilizing Adenosine Diphosphate (ADP) and phosphorylating it to Adenosine Triphosphate (ATP). Phosphorylation of ADP is typically through either an oxidative or substrate level process.

What is Oxidative Phosphorylation?

The oxidative phosphorylation of ADP happens through cellular respiration wherein enzymes are used to oxidize nutrients. This process is very efficient in releasing energy in biological systems when compared to fermentation or anaerobic glycolysis. Unlike oxidative phosphorylation, substrate level phosphorylation does not couple phosphorylation and oxidation.

What is Substrate Level Phosphorylation?

Substrate level phosphorylation is a type of ADP phosphorylation that occurs in the cytoplasm of cells (glycolysis) and in the mitochondria (Krebs cycle). Energy storage and generation occurs more quickly than oxidative phosphorylation. Therefore, substrate level phosphorylation is considered less efficient than oxidative phosphorylation.

Substrate Level Phosphorylation - ATP-ADP Cycle Diagram

Diagram featuing the ATP-ADP Cycle in substrate level phosphorylation. Click for larger image.

Phosphorylation in Aerobic Respiration

The diagram below demonstrates oxidative phosphorylation and substrate level phosphorolation in aerobic respiration.

Diagram of phosphorylation in Aerobic Respiration

The above diagram demonstrates oxidative phosphorylation and substrate level phosphorylation in aerobic respiration. Click the image view a printable version.

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