The two stages of Krebs cycle are:
- Citric Acid Production: Pyruvic acid from glycolysis reacts to form acetyl-CoA, which then enters the Krebs cycle. In the process, a molecule of carbon dioxide is produced and 2 high-energy electrons are passed to NAD+ to produce NADH. Acetyl-CoA combines with a 4-carbon compound in the Krebs cycle to produce citric acid.
- Energy Extraction: Through a series of many reactions, citric acid is broken down into a 5-carbon compound, and then a 4-carbon compound (releasing 2 carbon dioxide molecules along the way). This 4-carbon compound can then start the cycle over again by combining with acetyl-CoA. Energy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2.
The following are marked on the diagram:
Cytoplasm
Outer mitochondrial membrane
Pyruvic Acid
Inner mitochondrial membrane
Matrix
NAD+
NADH
CO2
CoA
Acetyl-CoA
Citric Acid
FADH2
FAD
ATP
ADP
To electron transport chain