Biomedical Engineering Reference
In-Depth Information
Cytosol
Glycolysis
Glucose
2 Pyruvate
Electron Transport Chain
Outside
2( NADH + H + )
6( NADH + H + )+ 2 FADH 2
2 FADHt 2
Glucose
Krebs
Cycle
2 Acetyl CoA
Mitochondria
H +
2
NADH
+
Glucose
2 FADH 2
+2 ATP
+2 ATP
+32 ATP
FIGURE 8.23 Cellular respiration consisting of three steps: glycolysis, Krebs cycle, and the electron transport
chain. The amount of ATP created or lost in each step is indicated at the bottom of the figure. A total of 36 mole-
cules of ATP are created from 1 molecule of glucose.
based on the needs of the cell for ATP. If there is an increased need for ATP, more mito-
chondria are produced.
We call the process of adding an inorganic phosphate to a molecule phosphorylation. We
call the use of
2 in the phosphorylation process oxidative phosphorylation. While the
overall chemical reaction in Eq. (8.85) looks simple enough, it consists of many enzyme cat-
alyzed reactions.
A carrier-mediated transport process is the mechanism postulated to move glucose into
the cell from the interstitial fluid. Ten enzyme catalyzed reactions take place in the cytosol
during glycolysis, 3 where a glucose molecule is broken down into two pyruvate
O
C 3 H 4 O ð Þ
molecules in which energy is consumed and produced. The overall reaction in glycolysis
is given by
NAD þ þ
C 6 H 12 O 6 þ
2
2
ADP þ
2
P !
ð
8
:
86
Þ
NADH þ H þ
2
C 3 H 4 O 3 þ
2
ð
Þ þ
2
ATP þ
2
H 2 O
NAD þ is nicotinamide adenine dinucleotide and when combined with two hydrogen,
where
NADH þ H þ :
NADH þ H þ is
forms
During the electron transport chain, each molecule of
used to create three molecules of ATP.
The next two steps occur in the mitochondria. The second step begins with the conver-
sion of pyruvate,
C 3 H 4 O 3 , into acetyl coenzyme A, followed by eight more major enzyme
catalyzed reactions called the Krebs cycle. 4 The overall result of the Krebs cycle is the
3 Glycolysis is also known as the Embden-Meyerhoff pathway.
4 The Krebs cycle is also known as the citric acid and tricarboxylic acid cycle.
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