Citric Acid Cycle

Carbohydrate Metabolism Overview
Overview Metabolism &
Energy Summary
 Elmhurst College
Form Acetyl CoA Citric Acid Cycle Summary Cori Cycle  Chemistry Department
Citric Acid Cycle Reactions Hormone Control    Virtual ChemBook

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Overview of Citric Acid Cycle

Introduction to the Citric Acid Cycle:

Under aerobic conditions the end product of glycolysis is pyruvic acid. The next step is the formation of acetyl coenzyme A (acetyl CoA) which is the initiator of the citric acid cycle. In carbohydrate metabolism, acetyl CoA is the link between glycolysis and the citric acid cycle.

The citric acid cycle is also known as the Krebs cycle or the tricarboxylic acid cycle. The citric acid cycle contains the final oxidation reactions, coupled to the electron transport chain, which produce the majority of the ATP in the body. Although we have only studied the formation of acetyl CoA from carbohydrates, it is also produced from the metabolism of fatty acids and amino acids which will be studied in later pages. The reactions of the citric acid cycle occur in the mitochondria which is also the location of the electron transport chain.

The overall reaction which occurs in the citric acid cycle may seem slightly odd. Actually, none of the compounds in the citric acid cycle appear in th equation since it is a cycle--the starting compound, oxaloacetic acid, is regenerated.

acetyl CoA + 3 H2O + 3 NAD+ + FAD + ADP ---> HSCoA + 2 CO2 + NADH + 3H+ + FADH2 + ATP

In the overall scheme of the metabolism of glucose, the citric acid cycle shows where the carbon dioxide comes from and starts the path of hydrogen and electrons into the electrontransport chain to produce water and trap energy as ATP.

The overall reaction for the metabolism of glucose is written:

C6H12O6 + 6 O2 -----> 6 CO2 + 6 H2O + energy

Link to: Rodney Boyer Animation of Citric Acid Cyle

Link to: Interactive Citric Acid Cycle (move cursor over arrows)
Jim Hardy, Professor of Chemistry, The University of Akron.

Link to: Great Animation of entire Citric Acid Cycle - John Kyrk