In oxidative metabolism, the electron pairs liberated through the oxidation of glucose do not pass directly to O2. The direct oxidants are the coenzymes of various oxidoreductases. The reduced forms of these coenzymes, NADH and FADH2, then transfer these electrons into the electron transport system which is located on the mitochondrial matrix. ATP is formed through an energy coupling process that begins with reoxidation of NADH and FADH2. The electrons passing from NADH and FADH2 travel through a sequential oxidation-reduction process involving a long series of redox centers located within a series of protein complexes in the inner mitochondrial membrane. As electrons pass along the chain, protons are expelled from the mitochondrial matrix by various mechanisms. The free energy stored in the resulting concentration and electric potential gradient (proton motive force) drives the synthesis of ATP as the protons flow back to the mitochondrial matrix through the protein complex ATP synthase.
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Conceptual Vocabulary for Oxidative Phosphorylation
Glycolysis & Pyruvate Dehydrogenase
An anaerobic organism is any organism that does not require oxygen for growth.
Adenosine triphosphate is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer.
Glycolysis is the initial process of most carbohydrate catabolism serving the functions of producing ATP and NADH, pyruvate for the citric acid cycle, and a variety of other compounds which are important for biosynthesis.
Pyruvic acid is an alpha-keto acid which plays an important role in biochemical processes. It is an output of glycolysis.
Glucose 6-phosphate (also known as Robison ester) is glucose sugar phosphorylated on carbon 6.
Fermentation is respiration under anaerobic conditions with no external electron acceptor.
Ethanol fermentation is the biological process by which sugars such as glucose, fructose, and sucrose, are converted into ethanol and carbon dioxide.
A kinase, alternatively known as a phosphotransferase, is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific target molecules.
Phosphorylation is the addition of a phosphate group to a protein molecule or a small molecule.
Fructose 2,6-bisphosphate, is a metabolite that allosterically affects the activity of the enzymes phosphofructokinase 1 and fructose 1,6-bisphosphatase to regulate glycolysis and gluconeogenesis.
A futile cycle is when two metabolic pathways run simultaneously in opposite directions and have no overall effect other than wasting energy.
Fructose 6-phosphate (also known as the Neuberg ester) is fructose sugar phosphorylated on carbon 6. The beta-D-form of this compound is very common in cells.
L-lactate is constantly produced in animals from pyruvate in a process of fermentation during normal metabolism and exercise.
Lactic acid fermentation is a form of anaerobic respiration that occurs in some bacteria and animal cells in the absence of oxygen.
Adenosine monophosphate is an ester of phosphoric acid with the nucleoside adenosine. AMP consists of the phosphate group, the pentose sugar ribose, and the nucleobase adenine.
Substrate-level phosphorylation is a type of chemical reaction that results in the formation of ATP by the direct transfer of a phosphate group to ADP from a reactive intermediate.
The pyruvate decarboxylation reaction links the metabolic pathways glycolysis and the citric acid cycle.
In glycolysis and photosynthesis, 1,3-Bisphosphoglycerate (1,3BPG) is a transitional stage between glycerate 3-phosphate and glyceraldehyde 3-phosphate during the fixation or reduction, respectively, of carbon dioxide.
2-Phosphoglycerate (2PG) is a glyceric acid which serves as the substrate in the ninth step of glycolysis. It is catalyzed by enolase into phosphoenolpyruvate (PEP), the penultimate step in the conversion of glucose to pyruvate.
A hexokinase is an enzyme that phosphorylates a six-carbon sugar, a hexose, to a hexose phosphate.
Enolase, or 2-phospho-D-glycerate hydrolyase, is an enzyme that participates in glycolysis, catalyzing the conversion of 2-phosphoglycerate to phosphoenolpyruvate, the penultimate step in the conversion of glucose to pyruvate.
Pyruvate kinase is an enzyme involved in glycolysis, catalyzing the transfer of a phosphate group from phosphoenolpyruvate (PEP) to ADP, yielding a pyruvate molecule and producing one molecule ATP.
Pyruvate dehydrogenase complex (PDC) is a complex of three enzymes that transform pyruvate into acetyl-CoA.
The Entner-Doudoroff pathway in some prokaryotes describes a series of reactions that catabolize glucose to pyruvate using a different set of enzymes from those used in either glycolysis or the pentose phosphate pathway.
Aldolase A is an enzyme which catalyses one of the aldol reactions of glycolysis in which fructose 1,6-bisphosphate is broken down into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.