During glycolysis in the cytoplasm the glucose is broken down into pyruvate. From the Pyruvate, a two-carbon fragment is used to form acetyl-COA.
Acetyl-COA goes to the mitochondrion and enters the Krebs Cycle.
The two-carbon fragment of the acetyl-COA is transferred to a 4-carbon molecule to form a 6-carbon compound. This COA carrier molecule is released.
From this 6-carbon molecule, the carbon dioxide is released leaving behind a 5-carbon compound. Hydrogen is also removed and transferred to NAD⁺ to form NADH.
A second oxidation and decarboxylation occurs, releasing carbon dioxide and hydrogen and leaving behind a 4-carbon molecule. ATP molecule is also produced in this phase.
The 4-carbon molecule is again oxidized and releases hydrogen that forms the NADH and FADH₂.
The final 4-carbon molecule will then merge with the two-carbon fragment of acetyl-COA and the Krebs cycle will start again.
A single turn of the Krebs cycle will result to 1 ATP, 3 NADH, and 1 FADH2.