Download SURVEY OF BIOCHEMISTRY Citric Acid Cycle

SURVEY OF BIOCHEMISTRY
Citric Acid Cycle
1
Formation of Acetyl CoA
Acetyl CoA is a
metabolic
intermediate that
can be produced
from amino
acids, glucose
(via pyruvate),
and fatty acids
This rxn is the first of 5 dehydrogenase reactions.
Here oxidation of pyruvate to acetyl CoA
(and reduction of NAD+ to NADH) leads to the production of CO2.
2
Formation of Citrate
Citrate is a tricarboxylic acid. The citric acid cycle is sometimes
referred to as the Tricarboxylic Acid (TCA) Cycle.
3
Formation of Isocitrate
Notice that aconitase catalyzes this reaction in both directions!
4
Formation of Alpha-Ketoglutarate
Notice that the carbon that is cleaved off of isocitrate did not come
from the carbons in acetyl CoA!
This rxn is the second of 5 dehydrogenase reactions.
5
Formation of Succinyl-CoA
This rxn is the third of 5 dehydrogenase reactions.
Here a 5-C molecule is converted into a 4-C precursor.
6
Formation of Succinate
GTP is equivalent to an ATP in terms of the
energy yield from hydrolysis.
7
Formation of Fumarate
This rxn is the fourth of 5 dehydrogenase reactions.
FAD is the redox cofactor used by succinate dehydrogenase.
8
Formation of L-Malate
9
Formation of Oxaloacetate
This rxn is the fifth of 5 dehydrogenase reactions.
Oxaloacetate has now been regenerated so that it can react with a
new molecule of acetyl CoA to repeat the cycle.
10
ATP Accounting
Glycolysis
Glycolysis  TCA Cycle
TCA Cycle
ATP
2
0
0
GTP
0
0
2
NADH
2
2
6
FADH2
0
0
2
Each GTP is equivalent to 1 ATP
Each NADH is equivalent to 2.5 ATP’s
Each FADH2 is equivalent to 1.5 ATP’s
11
ATP Accounting
TOTAL
ATP
2
ATP Equivalents
2
GTP
2
2
NADH
10
25
FADH2
2
3
One molecule of
glucose gets
metabolized into
~32 ATP’s
Each GTP is equivalent to 1 ATP
Each NADH is equivalent to 2.5 ATP’s
Each FADH2 is equivalent to 1.5 ATP’s
12
Summary
• Read Chapter 17.1-17.4
• Learn each step of the TCA Cycle
–
–
–
–
Substrates
Products
Reactants
Cofactors
• Next Monday
– Mechanisms in the TCA Cycle
– Control of the TCA Cycle
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