Substrate-level phosphorylation

Substrate-level phosphorylation

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Substrate-level phosphorylation is a type of metabolism that results in the formation and creation of adenosine triphosphate
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

 (ATP) or guanosine triphosphate
Guanosine triphosphate
Guanosine-5'-triphosphate is a purine nucleoside triphosphate. It can act as a substrate for the synthesis of RNA during the transcription process...

 (GTP) by the direct transfer and donation of a phosphoryl (PO3) group to adenosine diphosphate
Adenosine diphosphate
Adenosine diphosphate, abbreviated ADP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside adenosine. ADP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase adenine....

 (ADP) or guanosine diphosphate
Guanosine diphosphate
Guanosine diphosphate, abbreviated GDP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside guanosine. GDP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase guanine....

 (GDP) from a phosphorylated reactive intermediate
Reactive intermediate
In chemistry a reactive intermediate is a short-lived, high energy, highly reactive molecule. When generated in a chemical reaction it will quickly convert into a more stable molecule. Only in exceptional cases can these compounds be isolated and stored, e.g. low temperatures, matrix isolation...

. By convention, the phosphoryl group that is transferred is referred to as a phosphate group.

An alternative way to create ATP is through oxidative phosphorylation
Oxidative phosphorylation
Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all aerobic organisms carry out oxidative phosphorylation to produce ATP,...

, which takes place during the process of cellular respiration
Cellular respiration
Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products. The reactions involved in respiration are catabolic reactions that involve...

, in addition to the substrate-level phosphorylation that occurs during glycolysis and the Krebs cycle. During oxidative phosphorylation, NADH is oxidized to NAD+, yielding 2.5 ATPs, and FADH2 yields 1.5 ATPs when it is oxidized. Oxidative phosphorylation uses electrochemical or chemiosmotic gradient of protons (H+) across the inner mitochondrial membrane to generate ATP from ADP, which is a key difference from substrate-level phosphorylation.