Question

The P:OP:O ratio is the amount of inorganic phosphate incorporated into ATP per atom of oxygen consumed. It represents the coupling of phosphorylation and oxidation. It takes into account the number of protons translocated per electron pair and the ratio of the number of protons needed to synthesize and transport ATP. Determine the relationship of the P:OP:O ratio to the ratio of the number of protons translocated per electron pair and the ratio of the number of protons needed to synthesize ATP and transport it to the cytoplasm.

Answer 1

For NADH; P:O = 2.5

For FADH ₂; P : O = 1.5

Step-by-step explanation:

The P:O (phosphate:oxygen) ratio represents the amount of inorganic phosphate, Pi used per atom of oxygen consume to synthesize ATP.

The Chemiosmotic theory predicts H⁺:O and H⁺:ATP ratios. Experimentally these appear to be 10 and 4 respectively when NADH is the substrate, equivalent to a P:O ratio of 2.5, and 6 and 4 respectively for FAD-linked substrates (e.g. succinate), equivalent to a P:O ratio of 1.5.

1. Electron flow from NADH to O₂ pumps protons at three sites to yield 3 ATP (P:O = 2.5)

For NADH: 10 H ⁺ translocated/O (2e -)

ATP/2e - = (10 H⁺/ 4 H +) = 2.5

2. Succinate (via FADH2) bypasses site 1 giving 2 ATP (P : O = 1.5)

For FADH ₂= 6 H ⁺/O(2e - )

ATP/2e - = (6 H +/ 4 H +) = 1.5