Answer: a) NADH
Step-by-step explanation:
The Krebs cycle NADH and FADH2 molecules that act as electron and proton transporters (e- and H +) are oxidized in the final reactions of cellular respiration, and the electrons and protons are captured by oxygen, the final acceptor.
The electron transport chain contains 3 large protein complexes in the mitochondrial inner membrane; a small protein - cytochrome c; and a non-protein component - ubiquinone (Q).
1. NADH + H + gives off electrons to ubiquinone (Q) in a reaction catalyzed by the enzyme NADH-Q reductase.
2. cytochrome reductase transfers electrons from ubiquinone to cytochrome c
3. Cytochrome C and electrons pass to oxygen in a reaction catalyzed by cytochrome oxidase.
For each pair of electrons carried in the respiratory chain from NADH + H + to the final acceptor, oxygen, 3 ATPs are formed.