Substrate level phosphorylation is a form of metabolic reaction that leads to the formation of adenosine triphosphate (ATP) and GTP. The reaction utilizes a higher energy level substrate to form a lower level energy form of a product. Gibbs free energy is applied in the transfer of a phosphoryl group to an ADP molecule or a GDP molecule to form an ATP or GTP molecule. Given that there is loss of energy in the process, substrate level phosphorylation is an exergonic reaction. The reaction does not require energy to proceed and thus proceeds spontaneously.
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