acetyl CoA
The entry compound for the Krebs cycle in cellular respiration; formed from a fragment of pyruvate attached to a coenzyme.

aerobic cellular respiration (air-OH-bik)
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. Aerobic means containing oxygen; referring to an organism, environment, or cellular process that requires oxygen.

allosteric regulation (AL-oh-STEER-ik)
Regulation occuring at a specific receptor site on an enzyme molecule remote from the active site. Molecules bind to the allosteric site and change the shape of the active site, making it either more or less receptive to the substrate.

anaerobic (an-air-OH-bik)
Lacking oxygen; referring to an organism, environment, or cellular process that lacks oxygen and may be poisoned by it.

ATP synthase
A protein complex that produces ATP.

adenosine triphosphate (ATP) (uh-DEN-oh-sin try-FOS-fate)
An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.

cytochrome (SY-toh-krome)
An iron-containing protein, a component of electron transport chains in mitochondria and chloroplasts.

electron transport chain
A group of molecules in the inner membrane of a mitochondrion that synthesize ATP by means of an exergonic slide of electrons. Thylakoid membranes of chloroplasts are also equipped with electron transport chains.

feedback inhibition
A method of metabolic control in which the end-product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.

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.

glycolysis (gly-KOL-eh-sis)
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.

Krebs 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 cellular respiration.

metabolism (meh-TAB-oh-liz-um)
The totality of an organismıs chemical processes, consisting of catabolic and anabolic pathways.

mitochondrial matrix
The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the Krebs cycle.

NAD+ (nicotinamide adenine dinucleotide)
A coenzyme present in all cells that helps enzymes transfer electrons during the redox reactions of metabolism.

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

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.

The gaining of electrons by a substance involved in a redox reaction.

The substance on which an enzyme works.