<P> In oxidative phosphorylation, the passage of electrons from NADH and FADH through the electron transport chain pumps protons out of the mitochondrial matrix and into the intermembrane space . This pumping generates a proton motive force that is the net effect of a pH gradient and an electric potential gradient across the inner mitochondrial membrane . Flow of protons down this potential gradient--that is, from the intermembrane space to the matrix--yields ATP by ATP synthase . Three ATP are produced per turn . </P> <P> Most of the ATP synthesized in the mitochondria will be used for cellular processes in the cytosol; thus it must be exported from its site of synthesis in the mitochondrial matrix . ATP outward movement is favored by the membrane's electrochemical potential because the cytosol has a relatively positive charge compared to the relatively negative matrix . For every ATP transported out, it costs 1 H. One ATP costs about 3 H. Therefore, making and exporting one ATP requires 4H The inner membrane contains an antiporter, the ADP / ATP translocase, which is an integral membrane protein used to exchange newly synthesized ATP in the matrix for ADP in the intermembrane space . This translocase is driven by the membrane potential, as it results in the movement of about 4 negative charges out of the mitochondrial membrane in exchange for 3 negative charges moved inside . However, it is also necessary to transport phosphate into the mitochondrion; the phosphate carrier moves a proton in with each phosphate, partially dissipating the proton gradient . After completing glycolysis, the Citric Acid Cycle, electrons transport chain, and oxidative phosphorylation, approximately 30 - 38 ATP are produced per glucose . </P> <P> The citric acid cycle is regulated mainly by the availability of key substrates, particularly the ratio of NAD to NADH and the concentrations of calcium, inorganic phosphate, ATP, ADP, and AMP . Citrate--the ion that gives its name to the cycle--is a feedback inhibitor of citrate synthase and also inhibits PFK, providing a direct link between the regulation of the citric acid cycle and glycolysis . </P> <P> In the presence of air and various cofactors and enzymes, fatty acids are converted to acetyl - CoA . The pathway is called beta - oxidation . Each cycle of beta - oxidation shortens the fatty acid chain by two carbon atoms and produces one equivalent each of acetyl - CoA, NADH, and FADH . The acetyl - CoA is metabolized by the citric acid cycle to generate ATP, while the NADH and FADH are used by oxidative phosphorylation to generate ATP . Dozens of ATP equivalents are generated by the beta - oxidation of a single long acyl chain . </P>

Which of the following is true of the molecule adenosine triphosphate