120
PANEL 2–8: Details of the 10 Steps of Glycolysis <GGGC>
For each step, the part of the molecule that undergoes a change is shadowed in blue,
and the name of the enzyme that catalyzes the reaction is in a yellow box.
CH2OH
STEP 1
Glucose is
phosphorylated by ATP to
form a sugar phosphate.
The negative charge of the
phosphate prevents passage
of the sugar
phosphate through the
plasma membrane,
trapping glucose inside
the cell.
CH2O P
O
+
OH
HO
O
hexokinase
ATP
OH
+
OH
HO
OH
glucose 6-phosphate
H
O
1CH2OH
C1
H
C
2
OH
HO
C
H
H
C
OH
3
4
H
C
5
phosphoglucose
isomerase
O
C
2
HO
H
OH
H
CH2O P
6
C
H
C
OH
3
4
C
2
3
OH
4
OH
(ring form)
+
P OH2C
CH2O P
HO
OH
OH
CH2O P
O
ATP
+
HO
+
fructose 1,6-bisphosphate
HO
C
O
C
H
H
C
OH
H
C
OH
CH2O P
aldolase
HO
C
O
C
H
H
(open chain form)
fructose 1,6-bisphosphate
dihydroxyacetone phosphate
+
C
OH
CH2O P
dihydroxyacetone
phosphate
O
H
CH2O P
C
H
triose phosphate isomerase
O
O
H
C
H
C
OH
CH2O P
glyceraldehyde 3-phosphate
glyceraldehyde
3-phosphate
+
H
OH
CH2O P
CH2OH
ADP
OH
CH2O P
C
HO
(open chain form)
phosphofructokinase
(ring form)
STEP 5
The other
product of step 4,
dihydroxyacetone
phosphate, is
isomerized to form
glyceraldehyde
3-phosphate.
5
1
fructose 6-phosphate
STEP 3
The new hydroxyl
P OH2C
CH2OH
O
group on carbon 1 is
phosphorylated by ATP, in
HO
preparation for the formation
of two three-carbon sugar
OH
phosphates. The entry of sugars
OH
into glycolysis is controlled at this
step, through regulation of the
fructose 6-phosphate
enzyme phosphofructokinase.
O
CH2OH
O
6
CH2O P
6
(open chain form)
P OH2C
P OH2C
OH
5
glucose 6-phosphate
STEP 4
The
six-carbon sugar is
cleaved to produce
two three-carbon
molecules. Only the
glyceraldehyde
3-phosphate can
proceed immediately
through glycolysis.
H+
OH
OH
glucose
STEP 2
A readily
reversible rearrangement of the chemical
6 CH2O P
structure
5
O
(isomerization)
moves the
4
1
carbonyl oxygen
OH
from carbon 1 to HO
2
OH
3
carbon 2, forming
a ketose from an
OH
aldose sugar. (See
Panel 2–4.)
(ring form)
+
ADP
CHAPTER 2 PANELS
121
STEP 6
H
O
The two molecules
of glyceraldehyde 3-phosphate
C
are oxidized. The energy
generation phase of glycolysis
H C OH +
begins, as NADH and a new
high-energy anhydride linkage
CH2O P
to phosphate are formed (see
Figure 2–73).
glyceraldehyde 3-phosphate
+
NAD+
C
H
P
1,3-bisphosphoglycerate
+
C
ADP
H
+
C
ATP
OH
CH2O P
CH2O P
1,3-bisphosphoglycerate
3-phosphoglycerate
O–
O
C
H
C
2
C
phosphoglycerate mutase
OH
H
C
CH2O P
2-phosphoglycerate
O–
O
C
C
enolase
O P
C
CH2OH
C
pyruvate kinase
O P
H2O
+
ATP
O–
O
+
+
phosphoenolpyruvate
O–
C
O P
CH2
2-phosphoglycerate
O
O–
O
C
H
O P
CH2OH
3
3-phosphoglycerate
STEP 9
The removal of
water from 2-phosphoglycerate
creates a high-energy enol
phosphate linkage.
O–
O
1
STEP 10 The transfer to
ADP of the high-energy
phosphate group that was
generated in step 9 forms
ATP, completing glycolysis.
O–
O
OH
STEP 8
The remaining
phosphate ester linkage in
3-phosphoglycerate, which has
a relatively low free energy of
hydrolysis, is moved from
carbon 3 to carbon 2 to form
2-phosphoglycerate.
ADP
+
C
+
H
C
O
CH2
CH3
phosphoenolpyruvate
pyruvate
NET RESULT OF GLYCOLYSIS
O–
O
C
CH2OH
O
HO
C
NADH
OH
ATP
O–
O
OH
O
CH3
ATP
OH
C
ATP
ATP
NADH
ATP
ATP
C
O
CH3
glucose
H+
OH
phosphoglycerate kinase
C
+
NADH
CH2O P
C
H
+
C
O P
O
STEP 7
The transfer
to ADP of the
high-energy phosphate
group that was
generated in step 6
forms ATP.
O P
O
glyceraldehyde 3-phosphate
dehydrogenase
In addition to the pyruvate, the net products are
two molecules of ATP and two molecules of NADH
two molecules
of pyruvate