NADH is oxidized by a series of catalytic redox carriers that are integral proteins of the inner mitochondrial membrane. The free energy change in several of these steps is very exergonic. Coupled to these oxidation reduction steps is a transport process in which protons (H+) from the mitochondrial matrix are translocated to the space between the inner and outer mitochondrial membranes. The redistribution of protons leads to formation of a proton gradient across the mitochondrial membrane. The size of the gradient is proportional to the free energy change of the electron transfer reactions. The result of these reactions is that the redox energy of NADH is converted to the energy of the proton gradient. In the presence of ADP, protons flow down their thermodynamic gradient from outside the mitochondrion back into the mitochondrial matrix. This process is facilitated by a proton carrier in the inner mitochondrial membrane known as ATP synthase. As its name implies, this carrier is coupled to ATP synthesis. Electron flow through the mitochondrial electron transport assembly is carried out through several enzyme complexes. Electrons enter the transport chain primarily from cytosolic NADH to mitochondrial NADH but can also be supplied by succinate (to mitochondrial FADH2) or by the glycerol phosphate shuttle via mitochondrial FADH2. The glycerol phosphate shuttle is a secondary mechanism for the transport of electrons from cytosolic NADH to mitochondrial carriers of the oxidative phosphorylation pathway. The primary cytoplasmic NADH electron shuttle is the malate-aspartate shuttle (see below). Two enzymes are involved in this shuttle. One is the cytosolic version of the enzyme glycerol-3-phosphate dehydrogenase (glycerol-3-PDH) which has as one substrate, NADH. The second is is the mitochondrial form of the enzyme which has as one of its\' substrates, FAD+. The net result is that there is a continual conversion of the glycolytic intermediate, DHAP and glycerol-3-phosphate with the concomitant transfer of the electrons from reduced cytosolic NADH to mitochondrial oxidized FAD+. Since the electrons from mitochondrial FADH2 feed into the oxidative phosphorylation pathway at coenzyme Q (as opposed to NADH-ubiquinone oxidoreductase [complex I]) only 2 moles of ATP will be generated from glycolysis. G3PDH is glyceraldehyde-3-phoshate dehydrogenase. Solution NADH is oxidized by a series of catalytic redox carriers that are integral proteins of the inner mitochondrial membrane. The free energy change in several of these steps is very exergonic. Coupled to these oxidation reduction steps is a transport process in which protons (H+) from the mitochondrial matrix are translocated to the space between the inner and outer mitochondrial membranes. The redistribution of protons leads to formation of a proton gradient across the mitochondrial membrane. The size of the gradient is proportional to the free energy change of the electron transfer reactions. The resul.

1. NADH is oxidized by a series of catalytic redox carriers that are integral proteins of
the inner mitochondrial membrane. The free energy change in several of these steps is very
exergonic. Coupled to these oxidation reduction steps is a transport process in which protons
(H+) from the mitochondrial matrix are translocated to the space between the inner and outer
mitochondrial membranes. The redistribution of protons leads to formation of a proton gradient
across the mitochondrial membrane. The size of the gradient is proportional to the free energy
change of the electron transfer reactions. The result of these reactions is that the redox energy of
NADH is converted to the energy of the proton gradient. In the presence of ADP, protons flow
down their thermodynamic gradient from outside the mitochondrion back into the mitochondrial
matrix. This process is facilitated by a proton carrier in the inner mitochondrial membrane
known as ATP synthase. As its name implies, this carrier is coupled to ATP synthesis. Electron
flow through the mitochondrial electron transport assembly is carried out through several
enzyme complexes. Electrons enter the transport chain primarily from cytosolic NADH to
mitochondrial NADH but can also be supplied by succinate (to mitochondrial FADH2) or by the
glycerol phosphate shuttle via mitochondrial FADH2. The glycerol phosphate shuttle is a
secondary mechanism for the transport of electrons from cytosolic NADH to mitochondrial
carriers of the oxidative phosphorylation pathway. The primary cytoplasmic NADH electron
shuttle is the malate-aspartate shuttle (see below). Two enzymes are involved in this shuttle. One
is the cytosolic version of the enzyme glycerol-3-phosphate dehydrogenase (glycerol-3-PDH)
which has as one substrate, NADH. The second is is the mitochondrial form of the enzyme
which has as one of its' substrates, FAD+. The net result is that there is a continual conversion
of the glycolytic intermediate, DHAP and glycerol-3-phosphate with the concomitant transfer of
the electrons from reduced cytosolic NADH to mitochondrial oxidized FAD+. Since the
electrons from mitochondrial FADH2 feed into the oxidative phosphorylation pathway at
coenzyme Q (as opposed to NADH-ubiquinone oxidoreductase [complex I]) only 2 moles of
ATP will be generated from glycolysis. G3PDH is glyceraldehyde-3-phoshate dehydrogenase.
Solution
NADH is oxidized by a series of catalytic redox carriers that are integral proteins of
the inner mitochondrial membrane. The free energy change in several of these steps is very
exergonic. Coupled to these oxidation reduction steps is a transport process in which protons
(H+) from the mitochondrial matrix are translocated to the space between the inner and outer
mitochondrial membranes. The redistribution of protons leads to formation of a proton gradient
across the mitochondrial membrane. The size of the gradient is proportional to the free energy
change of the electron transfer reactions. The result of these reactions is that the redox energy of
NADH is converted to the energy of the proton gradient. In the presence of ADP, protons flow

2. down their thermodynamic gradient from outside the mitochondrion back into the mitochondrial
matrix. This process is facilitated by a proton carrier in the inner mitochondrial membrane
known as ATP synthase. As its name implies, this carrier is coupled to ATP synthesis. Electron
flow through the mitochondrial electron transport assembly is carried out through several
enzyme complexes. Electrons enter the transport chain primarily from cytosolic NADH to
mitochondrial NADH but can also be supplied by succinate (to mitochondrial FADH2) or by the
glycerol phosphate shuttle via mitochondrial FADH2. The glycerol phosphate shuttle is a
secondary mechanism for the transport of electrons from cytosolic NADH to mitochondrial
carriers of the oxidative phosphorylation pathway. The primary cytoplasmic NADH electron
shuttle is the malate-aspartate shuttle (see below). Two enzymes are involved in this shuttle. One
is the cytosolic version of the enzyme glycerol-3-phosphate dehydrogenase (glycerol-3-PDH)
which has as one substrate, NADH. The second is is the mitochondrial form of the enzyme
which has as one of its' substrates, FAD+. The net result is that there is a continual conversion
of the glycolytic intermediate, DHAP and glycerol-3-phosphate with the concomitant transfer of
the electrons from reduced cytosolic NADH to mitochondrial oxidized FAD+. Since the
electrons from mitochondrial FADH2 feed into the oxidative phosphorylation pathway at
coenzyme Q (as opposed to NADH-ubiquinone oxidoreductase [complex I]) only 2 moles of
ATP will be generated from glycolysis. G3PDH is glyceraldehyde-3-phoshate dehydrogenase.