Terminology

Anaplerotic Processes - Pathways which provide molecular intermediates for the citric acid cycle. Literally, to "build up" intermediates.
Citric Acid Cycle - Central metabolic pathway through which most other metabolic pathways converge. Oxidizes tricarboxylic acids. An alternate pathway in some organisms is the glyoxylate pathway (Figure 14.3).
Coenzymes - An organic small molecule that binds to an enzyme and is essential for its activity but is not permanently altered by the reaction. Most of these compounds are derived metabolically from vitamins.
Dehydrogenases - A class of enzymes catalyzing oxidation/reduction reactions in which the hydrogen is lost from the electron donor. Succinate dehydrogenase is one such enzyme from the citric acid cycle.
Flavins - Compounds containing and isoalloxazine ring system that are capable of accepting two electrons. FAD and FMN are members of this class of molecules (Figure 14.7).
Glyoxylate Pathway - A central metabolic pathway present only in some organisms that bypasses the oxidative decarboxylations of the citric acid cycle (Figure 14.20).

Mitochondria - Eukaryotic cellular organelle where the citric acid cycle, fatty acid oxidation, and other processes occur.
NAD+/NADH Ratio - A critical measure of the oxygen metabolic state of a cell, this ratio has a significant effect on controlling the citric acid cycle by both substrate levels and allosteric mechanisms. Can be significantly affected by the rate of electron transport and oxidative phosphorylation.

Oxidation/Reduction Reactions - Reactions that involve gain of electrons (reduction) by one compound and loss of the same electrons (oxidation) by another. It is important to realize that for every reduction of one molecule, there is a corresponding oxidation of another. For example, in the citric acid cycle reaction - Succinate + FAD <=> Fumarate + FADH 2, succinate is oxidized to fumarate and FAD is reduced to FADH 2.
Oxidases - A class of enzymes catalyzing oxidation/reduction reactions in which molecular oxygen is the electron acceptor.

Oxidative Phosphorylation - Oxidative phosphorylation is a process in the mitochondria in which potential energy from electrons released by oxidation occurring in metabolic pathways, such as glycolysis and the citric acid cycle, is captured in the form of the chemical energy of ATP.

Oxygenases - A class of enzymes catalyzing oxidation/reduction reactions in which molecular oxygen combines directly with the substrate being oxidized.
Pentose Phosphate Pathway - Metabolic pathway involving metabolism of numerous sugars, mostly with five carbons. The pathway is a source of ribose for nucleotides and NADPH for biosynthesis (Figure 14.22).
Reducing Equivalents - 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.
Thioester - A high energy ester bond where sulfur is substituted for oxygen. Acetyl-CoA is a compound with such a bond.

Transamination - A chemical reaction in which two molecules - one, such as aspartic acid, containing an amine group, and another, such as -ketoglutarate, containing an -keto group, exchange these functional groups, producing oxalaoacetate and glutamate (in this case).
Vitamin - An organic compound required in the diet in trace amounts.