Biomedical Engineering Reference
In-Depth Information
q
K
2
CP
Þ
o
¼
K
7
q
K
2
CP
ð
Þ
o
ð
q
P
i
¼
K
q
K
2
CP
7
ð
Þ
o
q
K
2
C
Þ
i
¼
K
7
q
K
2
CP
Þ
o
K
8
q
K
2
C
ð
ð
Þ
i
ð
q
ADP
i
¼
K
q
ADP
i
9
3
Na
i
q
C
i
¼
K
q
K
2
C
Þ
i
K
q
C
i
q
8
ð
2
q
K
i
¼
K
8
q
K
2
C
Þ
i
J
K
D
ð
K
þ
out of the cytosol at a rate of
where we assume a flow of
J
K
D
due to diffusion, a flow of
Na
þ
into the cell at a rate of
J
Na
D
from diffusion, ATP into the cytosol from the mitochondria
at a rate of
Note that
there are other models that describe the Na-K pump based on different assumptions.
K
1
, and ADP into the mitochondria from the cytosol at a rate of
K
9
:
8.5 CELLULAR RESPIRATION: GLUCOSE METABOLISM
AND THE CREATION OF ATP
At this time we wish to discuss cellular respiration involving glucose metabolism in
more detail by describing the chemical processes that enable the body to create energy in
the form of ATP. As previously noted, ATP is the fuel that supports life's processes, where
energy is stored in the inorganic phosphate bonds. Energy is required to form these bonds
in ATP, and energy is released when the bonds are broken.
Cellular respiration is among the best-known metabolic pathways, with detailed models
going back to the 1960s. While much progress has been made, much uncertainty exists, and
the system is still under considerable research. Here we will provide sufficient coverage
based on the techniques in this chapter and focus on aerobic respiration that uses oxygen
to create ATP in the mitochondria.
Cellular respiration consists of three major steps: glycolysis, Krebs cycle, and the electron
transport chain, as illustrated in Figure 8.23. The first step occurs in the cytosol, and the two
other steps occur in the mitochondria. Each step is very complex, with an overall reaction
given by
C
H
O
þ
6
O
þ
36
ADP
þ
36
P
!
6
CO
þ
6
H
O
þ
36
ATP
ð
8
:
85
Þ
6
12
6
2
2
2
which consists of the oxidation of glucose
ð
C
H
O
Þ
to
CO
2
and
O
2
, and a reduction of
6
12
6
O
Once inside the cell, 1 M of glucose is transformed into 36 M of ATP by adding
an inorganic phosphate
2
to
H
O
:
2
to each ADP. While there is some adenosine monophosphate
(AMP) that, when combined with two inorganic phosphates, creates ATP, we will ignore
this part of the reaction in this section.
Mitochondria are the powerhouses of the cell that produces the ATP used by the cell.
A mitochondrion has two lipid bilayer membranes. The outer membrane is smooth and acts
like a typical membrane. The inner membrane has many infoldings that contain the oxida-
tive enzymes. Within the inner membrane is a cavity called the matrix that contains a
nucleus with DNA, ribosomes, and dissolved enzymes. The matrix enzymes work with
the oxidative enzymes to create ATP. The mitochondria's nucleus allows it to self-replicate
P
