1

SURVEY OF BIOCHEMISTRYCitric Acid Cycle

2

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.

3

Formation of Citrate

Citrate is a tricarboxylic acid. The citric acid cycle is sometimes referred to as the Tricarboxylic Acid (TCA) Cycle.

4

Formation of Isocitrate

Notice that aconitase catalyzes this reaction in both directions!

5

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.

6

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.

7

Formation of Succinate

GTP is equivalent to an ATP in terms of the energy yield from hydrolysis.

8

Formation of Fumarate

This rxn is the fourth of 5 dehydrogenase reactions.FAD is the redox cofactor used by succinate dehydrogenase.

9

Formation of L-Malate

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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.

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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

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ATP Accounting

TOTAL ATP Equivalents

ATP 2 2

GTP 2 2

NADH 10 25

FADH2 2 3

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

One molecule of glucose gets

metabolized into~32 ATP’s

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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