Biomedical Engineering Reference
In-Depth Information
8.5.3 Electron Transport Chain
The electron transport chain is the last step in the conversion of glucose into ATP,
as illustrated in Figure 8.26. It involves a series of enzyme catalyzed chemical reactions that
transfer electrons from
NADH
þ
H
þ
2
(donor molecules) to acceptor molecules.
Ultimately the electron transport chain produces 32 molecules of ATP from one molecule
of glucose through hydrogen oxidation, and also regenerates NAD and FAD for reuse in
glycolysis. The overall reaction is given by
ð
Þ
and
FADH
1
2
O
NADH
þ
H
þ
P
!
NAD
þ
þ
ð
Þ þ
þ
3
ADP
þ
3
4
H
O
þ
3
ATP
2
2
and
1
2
O
2
þ
FADH
2
þ
2
ADP
þ
2
P
!
FAD
þ
3
H
2
O
þ
2
ATP
ð
8
:
113
Þ
The electron transport chain activity takes place in the inner membrane and the space
between the inner and outer membrane, called the intermembrane space. In addition to one
molecule of ATP created during each Krebs cycle, three pairs of hydrogen are released and
bound to 3
NAD
þ
to create 3
NADH
þ
H
þ
to form
FADH
2
within the mitochondrial matrix. As described before, two cycles through the Krebs
cycle are needed to fully oxidize one molecule of glucose, and thus 6
ð
Þ
, and one pair of hydrogen is bound to
FAD
NADH
þ
H
þ
ð
Þ
and
2
FADH
2
molecules are created.
Mitochondrion
Outer Membrane
Inner Membrane
H
+
H
+
NAD
+
e
-
e
-
1
ADP
H
+
NADH
+
Q
FAD
H
+
H
+
FADH
2
e
-
e
-
H
2
O
2
1
Cytosol
H
+
+
ATP
2
O
2
2
C
Matrix
Intermembrane
Space
ADP
+
P
H
+
e
-
e
-
H
+
H
+
3
ATP
ATP
4
H
+
5
ADP
FIGURE 8.26
A simplified illustration of the mitochondrion electric transport chain. Hydrogen pumps are
labeled 1 (NADH dehydrogenase), 2 (cytochrome
bc
1
complex), and 3 (cytochrome c oxidase complex). Electron
carriers are labeled Q (Coenzyme Q) and C (cytochrome c). The conversion of ADP
to ATP is accomplished
in the protein channel 4 (ATP synthetase), which also moves hydrogen ions back into the matrix, where they are
used again in sites 1-3. Carrier mediated diffusion exchanges ATP and ADP between the matrix and the intermem-
brane space. Then ATP and ADP are exchanged between the intermembrane space and the cytosol by diffusion.
þ
P
