Krebs Cycle 2

This is the first reaction that actually is a part of the Krebs cycle. This reaction is a condensation reaction (a reaction that joins together two molecules) in which the 2-carbon acetate that was formed from pyruvate in the preceding reaction is attached to a 4-carbon molecule, oxaloacetate (OAA). The reaction creates the 6-carbon molecule (2 carbons from acetate and 4 from OAA) citrate. OAA is already present in the mitochondrion and is not to be oxidized to carbon dioxide in the Krebs cycle. In fact, the Krebs cycle will regenerate OAA from citrate through a series of oxidations and decarboxylations. The joining of the acetate to OAA requires energy and this energy comes from the removal of the coenzyme A from the acetate. Remember that the addition of the coenzyme A to acetate in the preceding reaction energized acetate.

Items to note about this reaction:

1. This is the first reaction of the Krebs cycle.
2. Acetyl CoA is the actual reactant of the entire Krebs cycle and represents the only carbons that are actually oxidized to carbon dioxide during the cycle and they are the only carbons that enter the Krebs cycle from the breakdown of nutrients.
3. This is not an oxidation thus no NADH is formed.
4. OAA is not oxidized during the cycle but is regenerated so that the cycle can continue.

   Scoreboard

   after 2 reactions

   ATP Produced	NADH Produced	FADH Produced	CO2 Produced	O2 Used
   0	1	0	1	0

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