| adenosine diphosphate (ADP) | a molecule that combines with inorganic phosphate to form ATP.
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| adenosine triphosphate (ATP) | the high-energy phosphate compound synthesized and used by cells to release energy for cellular work.
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| aerobic | in the presence of oxygen.
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| anaerobic | without oxygen.
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| ATPase | enzyme capable of breaking down ATP to ADP 1 Pi 1 energy.
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| ATP-PC system | term used to describe the metabolic pathway involving muscle stores of ATP and the use of phosphocreatine to rephosphorylate ADP. This pathway is used at the onset of exercise and during short-term, high-intensity work.
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| beta oxidation | breakdown of free fatty acids to form acetyl-CoA.
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| bioenergetics | the chemical processes involved with the production of cellular ATP.
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| cell membrane | the lipid-bilayer envelope that encloses cells. Called the sarcolemma in muscle cells.
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| chemiosmotic hypothesis | the mechanism to explain the aerobic formation of ATP in mitochondria.
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| coupled reactions | the linking of energy-liberating chemical reactions to "drive" energy-requiring reactions.
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| cytoplasm | the contents of the cell surrounding the nucleus. Called sarcoplasm in muscle cells.
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| electron transport chain | a series of cytochromes in the mitochondria that are responsible for oxidative phosphorylation.
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| endergonic reactions | energy-requiring reactions.
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| energy of activation | energy required to initiate a chemical reaction.
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| enzymes | proteins that lower the energy of activation and, therefore, catalyze chemical reactions. Enzymes regulate the rate of most metabolic pathways.
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| exergonic reactions | chemical reactions that release energy.
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| FAD | flavin adenine dinucleotide. Serves as an electron carrier in bioenergetics.
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| glucose | a simple sugar that is transported via the blood and metabolized by tissues.
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| glycogen | a glucose polymer synthesized in cells as a means of storing carbohydrate.
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| glycogenolysis | the breakdown of glycogen into glucose.
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| glycolysis | a metabolic pathway in the cytoplasm of the cell that results in the degradation of glucose into pyruvate or lactate.
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| inorganic | relating to substances that do not contain carbon (C).
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| inorganic phosphate | (Pi) a stimulator of cellular metabolism; split off, along with ADP, from ATP when energy is released; used with ADP to form ATP in the electron transport chain.
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| isocitrate dehydrogenase | rate-limiting enzyme in the Krebs cycle that is inhibited by ATP and stimulated by ADP and Pi.
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| Krebs cycle | metabolic pathway in the mitochondria in which energy is transferred from carbohydrates, fats, and amino acids to NAD for subsequent production of ATP in the electron transport chain.
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| lactic acid | an end product of glucose metabolism in the glycolytic pathway; formed in conditions of inadequate oxygen and in muscle fibers with few mitochondria.
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| mitochondrion | the subcellular organelle responsible for the production of ATP with oxygen; contains the enzymes for the Krebs cycle, electron transport chain, and the fatty acid cycle.
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| molecular biology | branch of biochemistry involved with the study of gene structure and function.
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| NAD | coenzyme that transfers hydrogen and the energy associated with those hydrogens; in the Krebs cycle, NAD transfers energy from substrates to the electron transport chain.
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| nucleus | membrane-bound organelle containing most of the cell's DNA.
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| organic | describes substances that contain carbon.
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| oxidative phosphorylation | mitochondrial process in which inorganic phosphate (Pi) is coupled to ADP as energy is transferred along the electron transport chain in which oxygen is the final electron acceptor.
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| phosphocreatine | a compound found in skeletal muscle and used to resynthesize ATP from ADP.
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| phosphofructokinase | rate-limiting enzyme in glycolysis that is responsive to ADP, Pi, and ATP levels in the cytoplasm of the cell.
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