947
APPENDIX C
Note in figures C.1 and C.2 that twelve pairs of hydrogen
atoms are released during the complete breakdown of one glucose
molecule—two pairs from glycolysis, two pairs from the conver-
sion of pyruvic acid to acetyl coenzyme A (one pair from each of
two pyruvic acid molecules), and eight pairs from the citric acid
cycle (four pairs for each of two acetyl coenzyme A molecules).
High-energy electrons from ten pairs of these hydrogen
atoms produce thirty ATP molecules in the electron transport
Matrix
Matrix
Cristae
Inner
membrane
Intermembrane
space
Intermembrane space
Co Q
Cyt C
Enzyme
complex
1
2 H
+
2 H
+
2 H
+
6 H
+
NADH + H
+
NAD
+
1
/
2
O
2
+ 2 H
+
H
2
O
3 ADP + 3 P
i
2e
2e
2e
Enzyme
complex
2
Enzyme
complex
3
ATP
synthase
Outer
membrane
Outer
membrane
Inner
membrane
3 ATP
chain. Two pairs enter the chain differently and form four ATP
molecules. Because this process of forming ATP involves both
the oxidation of hydrogen atoms and the bonding of phosphate
to ADP, it is called oxidative phosphorylation. Also, there is a
net gain of two ATP molecules during glycolysis, and two ATP
molecules form by direct enzyme action in two turns of the citric
acid cycle. Thus, a maximum of thirty-eight ATP molecules form
for each glucose molecule metabolized.
FIGURE C.3
High energy electrons moving down the electron transport chain force hydrogen ions into the space between the
mitochondrial membranes. This sets up a gradient for hydrogen ions to diF
use back into the matrix by way of ATP synthase, which
converts much of their energy into ATP.
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