PANEL 2–8 Details of the 10 Steps of Glycolysis
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.
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.
CH2OH
CH2O P
O
HO
O
hexokinase
+
OH
ATP
OH
+
OH
HO
OH
glucose 6-phosphate
H
O
1CH2OH
C1
H
C
OH
HO
C
H
H
C
OH
H
H
C
OH
H
2
3
4
5
phosphoglucose
isomerase
C
O
C
H
C
OH
C
OH
2
HO
CH2O P
6
(open chain form)
3
4
5
The sixSTEP 4
carbon sugar is
cleaved to produce
two three-carbon
molecules. Only the
glyceraldehyde
3-phosphate can
proceed immediately
through glycolysis.
P OH2C
phosphofructokinase
+
HO
4
OH
1
HO
2
3
OH
(ring form)
P OH2C
CH2O P
O
ATP
+
HO
OH
ADP
+
H+
OH
OH
fructose 6-phosphate
fructose 1,6-bisphosphate
CH2O P
C
CH2O P
O
HO
OH
OH
(ring form)
CH2O P
O
HO
C
H
H
C
OH
H
C
OH
aldolase
HO
O
C
H
dihydroxyacetone
phosphate
O
H
CH2O P
dihydroxyacetone phosphate
+
C
C
OH
CH2O P
triose phosphate isomerase
O
O
H
H
CH2O P
CH2OH
C
C
H
(open chain form)
fructose 1,6-bisphosphate
STEP 5
The other
product of step 4,
dihydroxyacetone
phosphate, is
isomerized to form
glyceraldehyde
3-phosphate.
5
OH
P OH2C
CH2OH
O
fructose 6-phosphate
CH2OH
O
P OH2C
6
CH2O P
6
(open chain form)
glucose 6-phosphate
The new hydroxyl
STEP 3
group on carbon 1 is
phosphorylated by ATP, in
preparation for the formation
of two three-carbon sugar
phosphates. The entry of
sugars into glycolysis is
controlled at this step, through
regulation of the enzyme
phosphofructokinase.
H+
OH
OH
glucose
A readily
STEP 2
reversible rearrangement of the
6 CH2O P
chemical structure
5
O
(isomerization)
moves the
4
1
carbonyl oxygen
OH
from carbon 1 to
2
HO
OH
3
carbon 2, forming
a ketose from an
OH
aldose sugar. (See
Panel 2–4.)
(ring form)
+
ADP
C
H
C
OH
CH2O P
glyceraldehyde 3-phosphate
glyceraldehyde
3-phosphate