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aerobic respiration I (cytochrome c)

General Background Like |FRAME: Fermentation fermentation|, respiration is a process by which electrons are passed from an electron donor to a terminal electron acceptor. However, in respiration the electrons do not pass directly from the donor to the acceptor. Instead, they pass a number of membrane-bound electron carriers that function as a transport chain, passing the electrons from one to another in steps that follow the electrochemical gradients between the electron donor and the acceptor. Each oxidized member of the electron transfer chain (which can be |FRAME: Flavoproteins|, |FRAME: ETR-Quinones|, |FRAME: Cytochromes|, or other type of electron carrier) can be reduced by the reduced form of the preceding member, and the electrons flow through the chain all the way to the terminal acceptor, which could be oxygen in the case of aerobic respiration, or another type of molecule in anaerobic respiration. Known terminal acceptors include organic compounds (|FRAME: FUM|, |FRAME: DMSO|, or |FRAME: TRIMETHYLAMINE-N-O|), or inorganic compounds (|FRAME: NITRATE|, |FRAME: NITRITE|, |FRAME: NITROUS-OXIDE|, |FRAME: CHLORATE|, |FRAME: CPD0-1385|, |FRAME: MN+3 "oxidized manganese ions"|, |FRAME: FE+3 "ferric iron"|, gold, |FRAME: SELENATE|, |FRAME: ARSENATE|, |FRAME: SULFATE| and |FRAME: Elemental-Sulfur "elemental sulfur"|). During the process of electron transfer, a proton gradient is formed across the membrane due to three potential processes: 1. The use of some of the energy associated with the electron transfer for active pumping of protons out of the cell. 2. Exporting protons out of the cell during electron-to-hydrogen transfers. 3. Scalar reactions that consume protons inside the cell, or produce them outside the cell, without actually moving a proton from one compartment to another. Upon passage of protons back into the cytoplasm, they drive multisubunit |FRAME: EC-3.6.3.14 "ATP synthase"| enzymes that generate ATP. About This Pathway NADH and FADH2 are formed in the glycolytic and TCA cycles. Each of these energy-rich molecules has a pair of electrons with high transfer potential. The free energy liberated during transfer of those electrons can be used for synthesizing ATP. This electron transfer is performed by a series of four large electron carriers complexes also known as complex I-IV (electron transport chain or respiratory chain), present in the inner mitochondrial membrane. These complexes facilitate the passage of electrons from lower to higher redox potentials. Of those complexes, complex I and II are involved in the oxidation of NADH and FADH2. The flow of electrons resulting from this oxidation causes protons to be pumped from the matrix side to the intermembrane space. This flow generates a proton-motive force composed of a pH gradient and a membrane potential. Those protons flow back into the matrix through various routes. Particularly, protons flow back through the ATP-synthesizing complex embedded in the mitochondrial membrane leading to the synthesis of ATP. Aerobic respiration parallels the transport of electrons resulting from the oxidation of NADH and FADH2 with the creation of a proton gradient and accompanying membrane potential, leading to the synthesis of ATP |CITS: [DEY97]|. In contrast to the mitochondrial respiration in mammals and plants (this pathway), the oxidative phosphorylation in |FRAME: TAX-4932| via the respiration chain occurs without complex I. Instead Baker's yeast employs three NADH:ubiquinone oxidoreductases (type II - one internal, two external) which catalyze the reoxidation of cytosolic |FRAME:NADH| to provide |FRAME:NAD| (see |FRAME:PWY-7279|) |CITS:[23086143] [1900238] [9733747] [9696750]|.

from BIOCYC source record: META_PWY-3781
Type: pathway
Taxonomic scope
:
conserved biosystem
BSID:
139750

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