MIT Department of Biology
7.014 Introductory Biology, Spring 2005
7.014 Handout
Biochemistry V-VI
1
7.014 Glycolysis Reactions Handout
O
Note: for simplicity, H's are shown as stars (*).
P =
2
1
OH
O
C C
glucose
4
3
CH2 OH
OH OH OH
C C
C
O-
O-
6
5
P
O H
H
H
OH
C
OH
H
OH
OH
ATP
H
OH
ADP
OH
O
glucose-6-phosphate
C C
OH OH O P
C
C
C
C
OH
HO O
fructose-6-phosphate
C C
OH OH O P
C C C C
OH
ATP
ADP
P
fructose 1,6-di phosphate
O O
C C
P
OH OH O P
C C
C
OCH2
O
H
C
CH2 O
P
OH
H
OH
OH
split at this bond
1 2 3
P O O H
dihydroxyacetone H C C C H
phosphate
H
OH
+
4
5 6
OH O P
C
C
O
H
H H
3
2
1
OH O P
O
C
H
C H
C
C H
OH
H
glyceraldehyde-3-phosphate
+
(2 molecules of g3p,
therefore next reactions
are doubled)
glyceraldehyde-3-phosphate
H H
2
H
O
C
glyceraldehyde-3-phosphate H C
H C
+
O H
O P
H S
E
Note:
E
H
= enzyme
(glyceraldehyde
3-phosphate
dehydrogenase)
side chain of
cysteine in protein
H
O
H C
S
H C
These reactions
happen twice
for each glucose.
E
O H
O P
H C
H
transient intermediate
(substrate is covalently
bound to enzyme)
NAD +
NADH + H+
O
C
S
H C
H C
H
E
transient intermediate
O H
O P
Pi
(enzyme is released
H S
unchanged = catalyst)
E
1,3 diphosphoglycerate
O
C
O P
H C
O H
H C
O P
H
ADP
ATP
O
C O3-phosphoglyceric acid
H C
O H
H C
O P
H
3
O
These reactions
happen twice
for each glucose.
C O3-phosphoglyceric acid
H C O H
H C O P
H
O
C O2-phosphoglyceric acid
H C O P
H C O H
H
H2 O
O
C O
O
O
C O P
C
C
-
phospho-enol-pyruvate
(PEP)
C
H
H
"keto" form:
more stable
(low energy)
ADP
H
"enol" form:
less stable
(high energy)
ATP
O
C O-
pyruvate
NAD
O
-
C O
H C
O H
H C H
+
C
O
NADH + H+ H C H
H
or
This reaction recycles
the NADH in human
muscle cells when O2
is low or absent.
(Thiamine – a B-vitamin
is required for this step)
O C
H
lactate
H
+
C
O
NADH + H+
NAD +
O
H C H This reaction recycles
NADH in yeast (and
H
some bacteria) when
O2 is absent.
O
H
H C H
H C H
H
ethanol
4
ATP & ADP
ATP
ADP
NH2
N
N
A
O-
N
N
H
O
H CH2
O-
O P
O P
O
O
O P O
O
Pi
H
H
O-
OH
OH
R
NAD + & NADH
H
H
H
nicotinamide: a vitamin for
humans (a.k.a. niacin) but
not for yeast or E. coli
O
C NH
2
N
NAD = N icotinamide Adenine Dinucleotide
H
R P P
NAD +
H
H
H
A
R
+ 2 e - + H+
NAD + reduced to NADH
(another molecule is oxidized)
NADH oxidized to NAD+
(another molecule is reduced)
H
O
C NH
2
N
H
A
R P P R
NADH
5
Photosynthesis & Electron Transport
Photosynthesis:
Cyclic
Photophosphorylation
Generates H+ gradient
(used for ATP synthesis)
only.
Chl
2 e-
H+out
H+
in
light
Chl
PS I
Non-cyclic
Photophosphorylation
Chl
Generates H+ gradient
(used for ATP synthesis)
and NADPH.
Chl
2 e-
NADP+
2 eH+out
NADPH + H+
H+
in
light
H2 O
Chl
2 e- Chl
light
PS I
PS II
O2
6
Respiration
Electron Transport
NADH from glycolysis & Krebs' Cycle
is recycled using O2 and generating H+
gradient (used for ATP synthesis).
NADH + H+
2 e-
NAD +
H+
H+
in
in
H+out
H+out
H+
H+
in
in
H+out
H+out
O2
H2 O
ATP Synthesis from H+ Gradient
(H+ gradient is generated by electron transport in photosynthesis & respiration)
H+ - driven ATP synthetase
(proton ATPase)
electron-transfer-driven
proton pump
H+
H+
high [H +]
membrane
2 e- + 2 H +
2 e- + 2 H +
low [H+]
ADP + P i
ATP
7