Terminology

2,4-Dinitrophenol (DNP) - A chemical which permeabilizes the inner mitochondrial membrane to protons and uncouples oxidative phosphorylation from electron transport. Another such chemical is FCCP.
Amytal - Barbiturate drug that inhibits electron transport by blocking electron flow between NADH and coenzyme Q (Figure 15.9).
Anaerobic - Refers to the absence of oxygen or the absence of a need for it; processes that must or can occur without oxygen are called anaerobic processes.
Antimycin A - A Streptomyces antibiotic that inhibits electron transport by blocking electron flow from cytochrome b to c 1 (Figure 15.9).
Antioxidants - Compounds that help prevent oxidative damage by scavenging oxygen radicals or by chemically reducing oxidized compounds.
Antiport - A transport system that moves two molecules in opposite directions across a membrane.
ATP Synthase Complex - Another name for Complex V (Figure 15.14).
Azide - An inhibitor of electron transport that works by inhibiting cytochrome oxidase (Complex IV). This compound reacts with the oxidized form of the complex (Figure 15.9).
Carbon Monoxide - An inhibitor of electron transport that works by inhibiting cytochrome oxidase (Complex IV). This compound reacts with the reduced form of the complex (Figure 15.9).
Chemiosmotic Coupling - Widely accepted model, originally proposed by Peter Mitchell, that explains the synthesis of ATP in oxidative phosphorylation .
Citric Acid Cycle - Major cyclic oxidative pathway by which acetyl-CoA is metabolized (Figure 15.1).
Coenzyme Q (ubiquinone or CoQ) - Electron acceptor from Complexes I and II of the respiratory chain. It donates electrons to Complex III (Figure 15.3).
Coupling - A phenomenon where two processes are linked with one another such that they are interdependent.
Cristae - Infoldings of the mitochondrial inner membrane that project inside of the mitochondrion (Figure 15.2).
Crossover Point - The place in an electron transport system where a respiratory inhibitor has blocked electron flow. Electron carriers before the block are reduced and carriers after the block are oxidized.
Cyanide - An inhibitor of electron transport that works by inhibiting cytochrome oxidase (Complex IV). This compound reacts with the oxidized form of the complex (Figure 15.9).
Cytochrome Oxidase - A multiprotein complex containing cytochromes a and a 3 of Complex IV (Figure 15.10).
Cytochromes - A group of red-brown heme proteins in the respiratory chain.
Difference Spectra - Laboratory technique that exploits differences in the absorption spectra of oxidized and reduced electron carriers to detemine the oxidation state of each (Figure 15.8).
Dihydroxyacetone Phosphate/Glycerol-3-phosphate Shuttle - A system for transporting electrons from NADH to the electron transport system. It is found in brain and insect flight muscle (Figure 15.11).

Electron Acceptor - In reactions involving oxidation and reduction, the molecule which is reduced is the electron acceptor. Cells commonly use a class of molecules such as flavins and nicotinamides as electron acceptors.

Electron Donor - In reactions involving oxidation and reduction, the molecule which is oxidized. For example, in the citric acid cycle reaction - Succinate + FAD <=> Fumarate + FADH 2, succinate is the electron donor.
Electrochemical Gradient - A gradient of electrical charge brought about by uneven distribution of charge. The mitochondria have such a gradient as a result of proton pumping. Also called proton motive force (pmf) (Figure 15.15).
Electron Transport Chain - A set of proteins and other electron-carrying molecules in the inner membrane of the mitochondrion.
Endergonic - In a nonisolated system, a process that is accompanied by a positive change in free energy (positive G) and therefore is thermodynamically not favored.
Exergonic - In a nonisolated system, a process that is accompanied by a negative change in free energy (negative G) and therefore is thermodynamically favored.
F 0F 1 Complex - ATP Synthase Complex, also known as Complex V (Figure 15.14).
F 1 Spheres - Knoblike structures on the surface of the cristae of mitochondria that are part of Complex V.
Flavin Adenine Dinucleotide (FAD), oxidized - Flavin molecule capable of carrying electrons produced in biological oxidations (Figure 15.1).
Flavin Adenine Dinucleotide (FADH 2), reduced - Flavin molecule that carries electrons. Figure 15.1
Flavin Mono-Nucleotide (FMN) - Prosthetic group of NADH Dehydrogenase.
Glutathione - A biological antioxidant that chemically reduces oxidized sulfurs in proteins. It also helps reduce peroxides.
Heme A - A modified type of heme found in cytochromes a and a 3 (Figure 15.6).
Ionophore - A molecule that permits movement of charged molecules across a membrane.
Iron-Sulfur Centers - Electron carrying groups within the iron-sulfur proteins. They consist of nonheme iron complexed to sulfur (Figure 15.4).
Iron-Sulfur Proteins - Electron carrying proteins in the respiratory chain that contain iron-sulfur centers (Figure 15.3).
Mitochondrial Inner Membrane - Distinct mitochondrial structure that is not freely permeable to most metabolites. It contains the complexes of the electron transport system (Figure 15.2).
Mitochondrial Intermembrane Space - Region located between the inner and outer mitochondrial membranes (Figure 15.2).
Mitochondrial Matrix - Free space within the mitochondria bounded by the cristae. Contains enzymes of the citric acid cycle, fatty acid oxidation, amino acid oxidation, and pyruvate oxidation (Figure 15.2).
Mitochondrial Outer Membrane - Distinct structure surrounding mitochondria that is fairly permeable to most biological metabolites (Figure 15.2).
NAD+ - The oxidized form of NADH. It is a common acceptor of electrons produced in biological oxidations (Figure 15.1)
NADH - The reduced form of NAD+, produced by transfer of electrons in biological oxidation. It can either donate electrons and reduce another biological molecule or can transfer electrons to the electron transport system (Figure 15.1)
NADH Dehydrogenase - Another name for Complex I that describes its enzymatic function.
Nernst Equation - An equation that relates the electrical potential across a membrane to the concentrations of ions on either side of the membrane.
Nigericin - An antibiotic that acts as a potassium/proton antiport.
Oligomycin - An inhibitor of oxidative phosphorylation that acts by binding to a specific protein in the F 0 complex .
Oxidation - A process involving the loss of electrons by a molecule. Accompanies a reduction.
Oxidized Electron Carrier - An electron carrier that has lost its electrons, such as NAD+, NADP+, or FAD.
P/O Ratio - Quantity of ATP synthesized per mole of substrate oxidized in isolated mitochondria.
Perferryl Ion - A highly reactive iron-oxygen intermediate generated as a result of P-450 action. The highly reactive group can abstract a hydrogen atom, even from an unreactive substrate, such as a hydrocarbon (Figure 15.25)
Phagocytosis - A defense mechanism of white blood cells against infectious agents using hydrogen peroxide and superoxides to kill the invading cells after they have been engulfed.
Proton Gradient - Produced by pumping of protons during movement of electrons through the complexes of the electron transport system. It is the energy source used in oxidative phosphorylation to make ATP (Figure 15.2)
Protoporphyrin IX - Chemical form of the iron complexing moiety in the cytochrome proteins.
Redox - A termed used as a shorthand designation of reduction-oxidation.
Reduced Electron Carrier - An electron carrier that is carrying electrons, such as NADH, NADPH, or FADH 2.
Reducing Equivalent - An amount of a reducing compound that donates the equivalent of 1 mole of electrons in an oxidation-reduction reaction. The electrons may be expressed in the form of hydrogen atoms.
Reduction - A process involving the gain of electrons by a molecule. Accompanies an oxidation.
Respiration (Cellular) - With respect to energy metabolism, the process in which cellular energy is generated through the oxidation of nutrient molecules with O 2 as the ultimate electron acceptor.
Respiratory Burst - A rapid intake of oxygen by white blood cells upon engulfing an invading bacterial cell. The oxygen is used to generate hydrogen peroxide and superoxide dismutase to kill the invader.
Respiratory Chain - The set of five multiprotein complexes, (named I, II, III, IV, V), coenzyme Q, and cytochrome c that make up the electron transport system and oxidative phosphorylation (Figure 15.2).
Respiratory Control - A phenomenon that results from tight coupling of oxidative phosphorylation and electron transport. Events that stop one of the processes, stop the other as well.
Rotenone - An inhibitor of electron transport that blocks electron flow between NADH and coenzyme Q (Figure 15.9).
Semiquinone - Chemical intermediate form of coenzyme Q during passage of electrons.
Standard Reduction Potential (E 0) A measure of the tendency of a reductant to lose electrons (Table 15.1)
Succinate-coenzyme Q Reductase - Another name for Complex II of the respiratory chain.
Superoxide Ion - A reactive species generated as a result of a one electron reduction of O 2, to form O 2-.
Tetramethyl-p-Phenylene Diamine (TMPD) - An artificial donor of electrons to the electron transport system. It accepts electrons from ascorbate and donates them to cytochrome c.
Transhydrogenase - An enzyme catalyzing transfer of electrons between NADPH and NAD+: NADPH + NAD+ <=> NADP+ + NADH.
Trifluorocarbonylcyanide phenylhydrazone (FCCP) - A chemical which permeabilizes the inner mitochondrial membrane to protons and uncouples oxidative phosphorylation from electron transport. Another such chemical is DNP.
Valinomycin - An ionophore that transports potassium ions.
Xenobiotics - Substances recognized by the body as foreign. They are frequently subjected to hydroxylation by P450 proteins.