Biomedical Engineering Reference
In-Depth Information
NADH
þ
H
þ
:
conversion of pyruvate into
CO
2
and
The overall reaction for the Krebs cycle
is given by
NAD
þ
þ
FAD
þ
Acetyl
-
CoA
þ
3
2
H
O
þ
ADP
þ
P
!
2
ð
8
:
87
Þ
NADH
þ
H
þ
CoA
SH
þ
2
CO
þ
FADH
þ
ATP
þ
3
ð
Þ
2
2
where
FAD
is flavin adenine dinucleotide, and when combined with two hydrogen forms
:
During the electron transport chain, each molecule of
2
is used to create
FADH
FADH
2
two molecules of ATP.
The last step in cellular respiration is the electron transport chain.
5
Each of the large
number of enzyme catalyzed reactions leading up to the electron transport chain contri-
butes only two molecules of ATP, four molecules of
FADH
2
, and eight molecules of
NADH
þ
H
þ
:
NADH
H
þ
and
During the electron transport chain,
FADH
2
are used to cre-
ate ATP by the oxidation of hydrogen atoms
Almost all of the energy created in cellular
respiration occurs in the electron transport chain in the metabolism of glucose (32 molecules
of ATP from one molecule of glucose). The overall reaction for the electron transport chain
is given by
.
1
2
O
2
þ
NADH
þ
H
þ
P
!
NAD
þ
þ
ð
Þ þ
3
ADP
þ
3
4
H
2
O
þ
3
ATP
and
1
2
O
FADH
þ
þ
2
ADP
þ
2
P
!
FAD
þ
3
H
O
þ
2
ATP
ð
8
:
88
Þ
2
2
2
The analysis in this section illustrates some of the major steps in converting glucose into
ATP. To maximize the amount of energy created from glucose, many reactions occur, rather
than a direct reaction of glucose into one ATP, water, and carbon dioxide
Using a series of
reactions in the cytosol and the mitochondria, a total of 36 molecules of ATP are created
from one molecule of glucose. We focus more detail on glycolysis and the Krebs cycle
and a broader treatment of the electron transport chain. We assume that the process of
transporting glucose into the cell occurs via a carrier-mediated transport and begins the gly-
colysis of glucose in the cytosol.
.
8.5.1 Glycolysis
Glycolysis involves 10 enzyme catalyzed reactions in the cytosol, which transform one
glucose molecule into two molecules of pyruvic acid, as shown in Figure 8.24. The interme-
diate complex reactions of the substrates and enzymes are not shown in Figure 8.24 for sim-
plicity. However, they are included in the differential equations using a reaction rate
constant for the intermediate complex given by
B
i
that corresponds to the reaction rate
K
i
:
for each
glucose molecule is seen during glycolysis. The major output of glycolysis is the creation of
2 pyruvate molecules from one molecule of glucose.
As shown in Figure 8.23, a net gain of 2 molecules of ATP and 2
ð
NADH
þ
H
þ
Þ
5
The electron transport chain is also known as the chemiosmotic mechanism.
