Essential Cell Biology 5th edition

436
PANEL 13–1 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. Reactions represented by double arrows ( ) are readily reversible, whereas those represented by
single arrows ( ) are effectively irreversible. To watch a video of the reactions of glycolysis, see Movie 13.1.
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.
HO
CH 2 OH
O
OH
OH
glucose
OH
hexokinase
HO
CH 2 O P
O
+ ATP
+ ADP +
OH
OH
OH
glucose 6-phosphate
H +
STEP 2
A readily reversible
rearrangement of the
chemical structure
(isomerization)
moves the carbonyl 4
oxygen from
carbon 1 to
carbon 2, forming
a ketose from an
aldose sugar.
(See Panel 2–4,
pp. 72–73.)
HO
6 CH 2 O
5
OH
3
P
O
2
OH
(ring form)
1
OH
O H
C1
H C
2
OH
HO C
3
H
H C
4
OH
H C
5
OH
CH
6 2 O P
(open-chain form)
1CH 2 OH
phosphoglucose C O
2
isomerase P OH 2 C CH 2 OH
HO C H
6 O
1
3
5 HO 2
H C OH
4
OH
4 3
H C OH
OH
5
(ring form)
CH
6 2 O P
(open-chain form)
glucose 6-phosphate
fructose 6-phosphate
STEP 3
The new hydroxyl group on
P
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.
OH 2 C O CH 2 OH
P OH 2 C O CH 2 O P
HO + ATP
phosphofructokinase
HO + ADP + H +
OH
OH
OH
OH
fructose 6-phosphate
fructose 1,6-bisphosphate
CH 2 O
P
CH 2 O
P
STEP 4
The six-carbon sugar is
cleaved to produce
two three-carbon
molecules. Only the
glyceraldehyde
3-phosphate can
proceed immediately
through glycolysis.
P
OH 2 C O CH 2 O
HO
OH
OH
(ring form)
P
HO
H
H
C O
C H
C OH
C OH
CH 2 O P
aldolase
HO
C
C
H
O
H
+
H
H
C
C
O
CH 2 O
OH
P
(open-chain form)
fructose 1,6-bisphosphate
dihydroxyacetone
phosphate
glyceraldehyde
3-phosphate
STEP 5
The other product of step 4,
dihydroxyacetone phosphate,
is isomerized to form a second
molecule of glyceraldehyde
3-phosphate.
CH 2 OH
C
O
CH 2 O
P
dihydroxyacetone
phosphate
triose phosphate isomerase
H
H
C
C
O
OH
CH 2 O P
glyceraldehyde
3-phosphate
ECB5 Panel 13.01a