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