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Mitochondrial respiratory chain 2026-10-18

Figure 1.
Electron and proton routes in the mitochondrial respiratory chain
. Original qualitative schematic. Blue arrows follow reducing equivalents; orange arrows denote outward proton transfer and green arrows denote return through ATP synthase. The inner mitochondrial membrane separates the mitochondrial matrix from the intermembrane space. Arrow widths encode no reaction rates or stoichiometry. The chemical protons consumed in forming water are distinct from pumped protons; the sketch omits transport of ADP and inorganic phosphate. Details.

For an original Electron balance, supply exactly

6 μ mol

of NADH to an ideal preparation with no other electron donor or competing electron acceptor. The donor supplies

12 μ mol

of Electrons. Complete reduction of one oxygen molecule needs four Electrons, so the corresponding oxygen consumption is

3 μ mol

. Adding the two formal half-reactions makes the result explicit:

2 NADH O_{2} + 4 H^{+} + 4 e^{-} 2 NADH + O_{2} + 2 H^{+} ⟶ 2 NAD^{+} + 2 H^{+} + 4 e^{-}, ⟶ 2 H_{2} O, ⟶ 2 NAD^{+} + 2 H_{2} O .

The cancelling Electrons determine the donor-to-oxygen ratio. These chemical equations do not count transmembrane protons or determine an ATP yield. Chemical protons consumed in water formation and transported protons have different roles in the ledger.

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