This process contributes to the gradient used in chemiosmosis. The electrons are passed through a series of redox reactions, with a small amount of free energy used at three points to transport hydrogen ions across a membrane. The electron transport chain is composed of four large, multiprotein complexes embedded in the inner mitochondrial membrane and two small diffusible electron carriers shuttling electrons between them. The electron transport chain is the portion of aerobic respiration that uses free oxygen as the final electron acceptor of the electrons removed from the intermediate compounds in glucose catabolism. There is no comparison of the cyclic pathway with a linear one. One molecule of either GTP or ATP is produced by substrate-level phosphorylation on each turn of the cycle. The electrons temporarily stored in molecules of NADH and FADH 2 are used to generate ATP in a subsequent pathway. The citric acid cycle is a series of redox and decarboxylation reactions that remove high-energy electrons and carbon dioxide. Chemical potential energy stored within the glucose molecule has been transferred to electron carriers or has been used to synthesize a few ATPs. At this point, the glucose molecule that originally entered cellular respiration has been completely oxidized. The electrons are picked up by NAD +, and the NADH carries the electrons to a later pathway for ATP production. The carbon dioxide accounts for two (conversion of two pyruvate molecules) of the six carbons of the original glucose molecule. During the conversion of pyruvate into the acetyl group, a molecule of carbon dioxide and two high-energy electrons are removed. The resulting acetyl CoA can enter several pathways, but most often, the acetyl group is delivered to the citric acid cycle for further catabolism. ![]() In the presence of oxygen, pyruvate is transformed into an acetyl group attached to a carrier molecule of coenzyme A. 7.3 Oxidation of Pyruvate and the Citric Acid Cycle This produces a net gain of two ATP and two NADH molecules for the cell. Two ATP molecules are invested in the first half and four ATP molecules are formed by substrate phosphorylation during the second half. The second half of glycolysis extracts ATP and high-energy electrons from hydrogen atoms and attaches them to NAD +. ATP is invested in the process during this half to energize the separation. Glycolysis consists of two parts: The first part prepares the six-carbon ring of glucose for cleavage into two three-carbon sugars. It was probably one of the earliest metabolic pathways to evolve and is used by nearly all of the organisms on earth. Glycolysis is the first pathway used in the breakdown of glucose to extract energy. The two processes of ATP regeneration that are used in conjunction with glucose catabolism are substrate-level phosphorylation and oxidative phosphorylation through the process of chemiosmosis. When ATP is used in a reaction, the third phosphate is temporarily attached to a substrate in a process called phosphorylation. Energy derived from glucose catabolism is used to convert ADP into ATP. As ATP is used for energy, a phosphate group or two are detached, and either ADP or AMP is produced. The structure of ATP is that of an RNA nucleotide with three phosphates attached. It allows the cell to store energy briefly and transport it within the cell to support endergonic chemical reactions. ATP functions as the energy currency for cells. ![]() Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License. ![]() We recommend using aĪuthors: Mary Ann Clark, Matthew Douglas, Jung Choi Use the information below to generate a citation. Then you must include on every digital page view the following attribution: If you are redistributing all or part of this book in a digital format, Then you must include on every physical page the following attribution: ![]() If you are redistributing all or part of this book in a print format, Want to cite, share, or modify this book? This book uses the
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