Oxygen-dependent Pathway Quiz

See Krebs Cycle. Option C is correct. The Krebs cycle takes place in the mitochondrial matrix. Acetyl CoA, made from pyruvate by the link reaction, combines with oxaloacetate to form citrate, and a series of reactions then oxidises the carbon atoms, releasing carbon dioxide. The electrons and protons removed in these oxidation steps are transferred to NAD⁺ (and FAD), producing NADH (and FADH₂). These are the reduced carriers, and they provide the reducing power, meaning the supply of high-energy electrons, that is used by oxidative phosphorylation. For every glucose molecule (two turns of the cycle), the cycle gives 6 NADH, 2 FADH₂ and 2 GTP. NADH delivers its electrons to the electron transport chain on the inner mitochondrial membrane, and the energy released is used to make most of the cell's ATP. That is how the Krebs cycle is linked to ATP production.

• Site: The Krebs cycle takes place in the mitochondrial matrix.
• Output: Each glucose gives 6 NADH, 2 FADH₂ and 2 GTP.
• Link to ATP: NADH delivers its electrons to the electron transport chain, which makes most of the cell's ATP.

A helpful aid is to think of the Krebs cycle as a station that loads carriers: acetyl-CoA goes in, and loaded NADH and FADH₂ come out.