Oxidation of Pyruvate (Intermediate stage: oxygen required)

Goal: take pyruvate and put it into the Citric Acid Cycle (also known as the Krebs cycle), producing NADH and FADH2

Where in the cell: the mitochondria

In the presence of oxygen (aerobic conditions), the 2 molecules of pyruvate produced in glycolysis enter the mitochondria and are oxidized by NAD+, resulting in the formation of the intermediate acetyl-coA and NADH. Acetyl-coA represents a major intermediate in the respiration pathway and NADH stores potential energy (in the form of electrons) that will eventually drive ATP synthesis. In the process of oxidizing pyruvate, a carbon was released from the molecule in the form of carbon dioxide.


conversion of pyruvate.jpg



Products: If you recall, there are two pyruvate produced in glycolysis, so this reaction occurs two-times resulting in: (2) acetyl coA, (2) NADH, and (2) carbon dioxide. Acetyl coA is then shuttled into its next stop, the citric acid cycle.



Citric Acid Cycle (Tricarboxylic acid cycle)...oxygen required

Goal: chemical breakdown of acetyl CoA, producing ATP, NADH and FADH2, releasing Carbon dioxide

Where in the cell: within the matrix of the mitochondria

In the citric acid cycle, there are a series of oxidation-reduction reactions that harvest the remaining potential energy from the original carbohydrate. Acetyl-CoA enters the citric acid cycle and a series of 9 enzymatic steps that transfer energy and electrons from acetyl-CoA to coenzymes NAD+ and FAD. Energy is transferred to form 1 ATP molecule, 3 NADH molecules, and 1 FADH2 molecule during 1 "turn" of the citric acid cycle. This pathway is called a "cycle" because oxaloacetic acid (oxaloacetate) is involved in the first step and is regenerated in the last step.

citric acid cycle.jpg




6 NADH's are generated (3 per Acetyl CoA that enters)

2 FADH2 is generated (1 per Acetyl CoA that enters)

2 ATP are generated (1 per Acetyl CoA that enters)

4 CO2's are released (2 per Acetyl CoA that enters)


 Click on the following link for a brief tutorial of the Citric Acid Cycle:



Click on the link below to view an animation of the Citric Acid Cycle:



 Hyperlink to Labeling Activity 

 spacerToggle open/close quiz question

Value: 1
As a result of glycolysis, pyruvate oxidation and the citric acid cycle, only a small portion of the energy of glucose has been converted to ATP. At this point, the majority of the usable energy is contained in:


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