Chemistry 2100
Chapter 27
Metabolism
Metabolism is the sum of catabolism and anabolism.
2
Metabolism
Stages of Catabolism
• digestion: hydrolysis
• degradation: nutrients
acetyl CoA
• TCA Cycle: acetyl CoA
CO2 + NADH / FADH2
• oxidative phosphorylation: NADH / FADH2
ATP
Catabolic Pathways
• Two principal types of compounds
participating in the common catabolic
pathway are:
– AMP, ADP, and ATP: agents for the
storage and transfer of phosphate
groups.
– NAD+/NADH and FAD/FADH2: agents
for the transfer of electrons in biological
oxidation-reduction reactions
Adenosine Triphosphate
NH 2
N
N
N
O
N
O
O
CH 2 O P O P O P OH
O
OH
Ad
OH
OH
OH
OH
Ad
O
O
O
H2O
O P O P O P O
O
O
O
Ad
O
O P O
O
O
+
O
O P O P O
O
O
+ 7500 cal/mol
Ad
O
O
O
H2O
O P O P O P O
O
O
O
Ad
O
O P O
O
O
+
O
O P O P O
O
O
+ 7500 cal/mol
Ad
O
O
O
H2O
O P O P O P O
O
O
O
Ad
O
O P O
O
O
+
O
O P O P O
O
O
+ 7500 cal/mol
O
Ad
O
O
H2O
O P O P O P O
O
O
O
Ad
O
O P O
O
O
+
O
O P O P O
O
O
+ 31.4 kJ/mol
Coupled Reactions
(and why we need them)
O
4 00 0 cal/mo l +
R C OH +
O
HO R'
R C O R' +
H2 O
O
4 00 0 cal/mo l +
R C OH +
O
HO R'
R C O R' +
H2 O
O
4 00 0 cal/mo l +
R C OH +
O
HO R'
R C O R' +
H2 O
O
16.7 kJ/mol
+
R
C
O
OH
+
HO
R'
R
C
O R'
+
H2 O
O
2500 cal/mol +
R
C
O
OH
+
O
O
O P O P O P O
O
O
O
R C O
Ad
O
O
P O
O
Ad
O
+
O
O P O P O
O
O
O
2500 cal/mol +
R
C
O
OH
+
O
O
O P O P O P O
O
O
O
R C O
Ad
O
O
P O
O
Ad
O
+
O
O P O P O
O
O
O
2500 cal/mol +
R
C
O
OH
+
O
O
O P O P O P O
O
O
O
R C O
Ad
O
O
P O
O
Ad
O
+
O
O P O P O
O
O
O
10.5 kJ/mol
+
R
C
O
OH
+
O
O
O P O P O P O
O
O
O
R C O
Ad
O
O
P O
O
O
Ad
+
O
O P O P O
O
O
O
R C O
O
P O
Ad
O
+
HO
R'
O
R
C
O
O R'
+
O P O
O
Ad
+ 6000 cal/mol
O
R C O
O
P O
Ad
O
+
HO
R'
O
R
C
O
O R'
+
O P O
O
Ad
+ 6000 cal/mol
O
R C O
O
P O
Ad
O
+
HO
R'
O
R
C
O
O R'
+
O P O
O
Ad
+ 6000 cal/mol
O
R C O
O
P O
Ad
O
+
HO
R'
O
R
C
O
O R' +
O P O
O
Ad
+ 25.1 kJ/mol
O
R
C
OH +
HO
R'
+
ATP
O
R
C
O R' +
AMP +
PP + 14.6 kJ/mol
NAD+/NADH
– NAD+ is a two-electron oxidizing agent, and is reduced to
NADH.
– NADH is a two-electron reducing agent, and is oxidized to
NAD+. The structures shown here are the nicotinamide
portions of NAD+ and NADH.
H
O
C
NH2 + H+ + 2 e-
H H O
C
NH2
:
N
Ad
+
NAD
(oxidized form)
N
Ad
NADH
(reduced form)
– NADH is an electron and hydrogen ion transporting
molecule.
FAD/FADH2
– FAD is a two-electron oxidizing agent, and is reduced to
FADH2.
– FADH2 is a two-electron reducing agent, and is oxidized to
FAD.
– Only the flavin moiety is shown in the structures below.
O
H3 C
H3 C
N
N
N
Ad
FAD
NH
O
H3 C
+ 2H
+
+ 2e
H
N
O
-
H3 C
N
N
Ad H
FAD H 2
NH
O
Acetyl-CoA production
Acetyl-CoA Oxidation
Electron Transfer and Oxidative
Phosphorylation
Where does this all happen?
Net Effect of the Citric Acid Cycle
Acetyl-CoA + 3NAD+ + FAD + GDP + Pi + 2 H2O
2CO2 +3NADH + FADH2 + GTP + CoA + 3H+
•
carbons of acetyl groups in acetyl-CoA are
oxidized to CO2
• electrons from this process reduce NAD+ and FAD
• one GTP is formed per cycle, this can be
converted to ATP
• intermediates in the cycle are not depleted
Energy Yield
Oxidative Phosphorylation