Biomedical Engineering Reference
In-Depth Information
H
2
COPO
2
OH
COOH
COOH
Phosphoglycerate
kinase
Phosphogly-
ceromutase
O
2
C=O
OC O PO
3
2
HCOPO
3
H
2
COH
HCOH
H
2
COPO
2
3-Phosphoglycerate
(3PG)
OH
HO
OH
ATP
ADP
HO
1,3-Biphospho-glycerate
(BPG)
2-Phosphoglycerate
(2PG)
Glu cose
Glyceraldehyde phosphate
dehydrogenase
ATP
Hexokinase
Enolase
ADP
NADH
H
2
O
2
O PO
3
NAD
+
+ Pi
HC=O
H
2
COH
C=O
H
2
COPO
2
Dihydroxyacetone phosphate
(DHAP)
COOH
O
Triose phosphate
isomerase
HCOH
H
2
COPO
2
2
COPO
3
CH
2
OH
OH
HO
HO
Glyceraldehyde-3-phosphate
(G3P)
Glucose-6-phosphate (G6P)
Phosphoenolpyruvate
(PEP)
Glucose
phosphate
isomerase
Pyruvate
kinase
ADP
O
-
2
Aldolase
O PO
3
ATP
-
O
O
O
P
COOH
O
Phosphofructokinase
OH
HO
O
C = O
HO
HO
HO
ADP
2
ATP
O
PO
3
HO
CH
3
OH
Pyruvate
Fructose-6-phosphate
(F6P)
Fructose-1,6-biphosphate (FBP)
FIGURE 10.20
Bioreactions involved in the breakdown of glucose by glycolysis.
The first step in glycolysis is phosphorylation of glucose to glucose-6-phosphate (G6P)
by hexokinase. Phosphorylated glucose can be kept inside the cell. Glucose-6-phosphate
is converted to fructose-6-phosphate (F6P) by phosphoglucose isomerase, which is
converted to fructose-1,6-biphosphate (FBP) by phosphofructokinase. The first and the
third reactions are the only two ATP-consuming reactions in glycolysis. They are
irreversible.
The breakdown of one mole of fructose-1,6-biphosphate into one mole of dihydroxyac-
etone phosphate (DHAP) and one mole of glyceraldehyde-3-phosphate (G3P) by aldolase
is one of the key steps in glycolysis (e.g. C
6
to 2 C
3
). DHAP and G3P are in equilibrium. As
G3P is utilized in glycolysis, DHAP is continuously converted to G3P. One mole of glyc-
eraldehyde-3-phosphate is first oxidized with the addition of inorganic phosphate to 1,3-
biphosphoglycerate (BPG) by glyceraldehyde-3-phosphate dehydrogenase. BPG releases
one phosphate group to form ATP from ADP and is converted to 3-phosphoglycerate
(3PG) by 3-phosphoglycerate kinase. 3PG is further converted to 2-phosphoglycerate
(2PG) by phosphoglyceromutase. Dehydration of 2PG to PEP by enolase is the next
step. PEP is further dephosphorylated to pyruvate (Pyr) by pyruvate kinase, with the
formationofanATP.ReactionsafterDHAP and G3P formation repeat twice during
glycolysis, i.e. there are two moles passing through to the final product of the glycolysis:
pyruvate.
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