Difference Between Substrate Level Phosphorylation and Oxidative Phosphorylation

Key Difference – Substrate Level Phosphorylation vs Oxidative Phosphorylation
 

Phosphorylation is a process that adds a phosphate group into an organic molecule by specific enzymes. It is an important mechanism that occurs in the cell to transfer energy or store energy in the form of high energy bonds between phosphate groups. ATP is formed in cells by phosphorylation. Other important phosphate-containing compounds are also synthesized by phosphorylation. There are different types of phosphorylation. Among them, substrate level phosphorylation and oxidative phosphorylation are common in cells. The key difference between substrate level phosphorylation and oxidative phosphorylation is that in substrate level phosphorylation, a phosphate group from a phosphorylated compound is directly transferred to ADP or GDP to form ATP or GTP without involving another molecules while in oxidative phosphorylation, nutrients or chemicals provide the energy to transfer a phosphate group to ADP and produce high energy ATP with the help of electron or H⁺ transport system.

CONTENTS
1. Overview and Key Difference
2. What is Substrate Level Phosphorylation
3. What is Oxidative Phosphorylation
4. Side by Side Comparison – Substrate Level Phosphorylation vs Oxidative Phosphorylation
5. Summary

What is Substrate Level Phosphorylation?

Direct transfer of a phosphate group from a substrate to ADP for the formation of high energy ATP is known as substrate level phosphorylation. This reaction is mostly catalyzed by the enzyme kinases. Phosphate group donor directly donates or transfers a phosphate group to ADP without the involvement of an intermediate between the donor and ADP. The phosphate group is transferred from the first molecule and received by the second molecule. The energy released during the breakage of the phosphate group is used to phosphorylation of ADP in substrate level phosphorylation, and it is known as reaction coupling. It can be shown by the following equation.

Glycolysis is the commonest example where ATP is synthesized via substrate level phosphorylation when two phosphoenol pyruvate molecules are converted into two pyruvate molecules by pyruvate kinase enzyme under aerobic or anaerobic conditions. Moreover, during the Krebs cycle, ATPs are produced via substrate level phosphorylation.

What is Oxidative Phosphorylation?

Oxidative phosphorylation is a process that phosphorylates ADP to synthesize ATP by transferring electrons along the electron transport chain at the final stage of the aerobic respiration. It uses NADH electron carriers and ATP synthase enzyme for the formation of ATP. The energy is produced from the redox reactions (proton gradient), and the phosphates come from the pool of inorganic phosphates. Oxidative phosphorylation needs molecular oxygen as the final electron acceptor. Hence, oxidative phosphorylation is feasible only under the aerobic conditions, and it occurs in the inner membrane of mitochondria. Oxidative phosphorylation is a process which yields a  higher number of ATP in the aerobic organisms.

Figure 02: Oxidative Phosphorylation

What is the difference between Substrate Level Phosphorylation and Oxidative Phosphorylation?

Summary – Substrate Level Phosphorylation vs Oxidative Phosphorylation

Substrate level phosphorylation is a process that converts ADP into ATP by direct transfer of a phosphate group from a phosphorylated compound to ADP. Oxidative phosphorylation uses proton gradient (H⁺ ion concentration gradient) generated in the electron transport chain to phosphorylate ADP into ATP in aerobic organisms. Substrate level phosphorylation can be seen in glycolysis and Krebs cycle. Oxidative phosphorylation can be seen in electron transport chain. This is the difference between substrate level phosphorylation and oxidative phosphorylation.

Reference:
1.” Substrate-level phosphorylation.” Substrate-level phosphorylation | Open Access articles | Open Access journals | Conference Proceedings | Editors | Authors | Reviewers | scientific events. N.p., n.d. Web. 26 Apr. 2017.
2. Natacha Bochud-Allemann. “Mitochondrial Substrate Level Phosphorylation Is Essential for Growth of Procyclic Trypanosoma brucei.” Journal of Biological Chemistry. N.p., 06 Sept. 2002. Web. 26 Apr. 2017
3.”Substrate-level phosphorylation.” Wikipedia. Wikimedia Foundation, 11 Apr. 2017. Web. 26 Apr. 2017
4.”Oxidative phosphorylation.” Wikipedia. Wikimedia Foundation, 05 Apr. 2017. Web. 26 Apr. 2017

Image Courtesy:
1. “2508 The Electron Transport Chain” By OpenStax College – Anatomy & Physiology, Connexions Web site.  Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia

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