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Krebs cycle strips off Carbon Dioxide and in the process reduces FAD and NAD for chemiosmosis.

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Krebs Cycle

It only takes place when oxygen is present.  Acetyl CoA is a 2 carbon molecule.  Oxaloacetate is a 4 carbon molecule.  CoA stands for Coenzyme A, a S (sulfur) containing, Vitamin B derived molecule that binds to Acetyl to make it very reactive (attach to oxaloacetate to form citrate).

Acetyl2 CO₂ + ATP + reduced coenzymes, 3 NADH and 1 FADH₂ (flavin adenine dinucleotide)

1. 2 C enter  as acetate
2. water removed; another added
3. 2 carbon dioxide composed of 2 different carbons leave as NADH is formed
4. carbon dioxide lost; NADH formed; product attaches to CoA
5. substrate-level phosphorylation
6. 2 H + FAD = FADH₂
7. Bonds rearranged by adding water
8. NADH formed; oxaloacetate receives acetate to continue the cycle

Beta Oxidation = fatty acidsAcetyl CoA

One gram of fat oxidized (degraded, cut down) yields 2 times as much ATP as 1 g of carbohydrate.

Next:  "Electron Transport Chain."