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a catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid.

cellular respiration

the most prevalent and efficient catabolic pathway for the production of ATP, in which oxygen is consumed as a reactant along with the organic fuel.

redox reaction

a chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction.


the loss of electrons from a substance involved in a redox reaction.


the addition of electrons to a substance involved in a redox reaction.

reducing agent

the electron donor in a redox reaction.

oxidizing agent

the electron acceptor in a redox reaction.


nicotinamide adenine dinucleotide, a coenzyme present in all cells that helps enzymes transfer electrons during the redox reactions of metabolism.

electron transport chain

a sequence of electron carrier molecules (membrance proteins) that shuttle electrons during the redox reactions that release energy used to make ATP.


the splitting of glucose into pyruvate. Glycolysis is the one metabolic pathway that occurs in all living cells, serving as the starting point for fermentation or aerobic respiration.

citric acid cycle

a chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules to carbon dioxide; occurs within the mitochondrion; the second major stage in cell respiration.

oxidative phosphorylation

the production of ATP using energy derived from the redox reactions of an electron transport chain.

substrate-level phosphorylation

the formation of ATP by directly transferring a phosphate group to ADP from an intermediate substrate in catabolism.

acetyl CoA

acetyl coenzyme A; the entry compound for the citric acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a coenzyme.


an iron-containing protein, a component of electron transport chains in mitochondria and chloroplasts.

ATP synthase

a cluster of several membrane proteins found in the mitochondrial crista (and bacterial plasma membrane) that function in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen ion concentration gradient to make ATP. ATP synthases provide a port through which hydrogen ions diffuse into the matric of a mitrochondrion.


an energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Most ATP synthesis in cells occurs by chemiosmosis.

proton-motive force

the potential energy stored in the form of an electrochemical gradient, generated by the pumping of hydrogen ions across biological membranes during chemiosmosis.


containing oxygen; referring to an organism, environment, or cellular process that requires oxygen.


lacking oxygen; referring to an organism, environment, or cellular process that lacks oxygen and may be poisoned by it.

alcohol fermentation

the conversion of pyruvate to carbon dioxide and ethyl alcohol.

lactic acid fermentation

the conversion of pyruvate to lactate with no release of carbon dioxide.

beta oxidation

a metabolic sequence of that breaks fatty acids down to two-carbon fragments that enter the citric acid cycle as acetyl CoA.

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