Q.18 How many ATP molecules are produced for each molecule of FADH2 oxidized via the respiratory chain?
1.0.5
2.1
3.1.5
4.2
FADH2 oxidation in the respiratory chain yields a specific ATP amount key for biology exams. The correct answer is 2 ATP per FADH2 molecule.
Correct Answer
Option 4: 2.
Each FADH2 molecule, oxidized via the electron transport chain (ETC) at Complex II, pumps fewer protons than NADH, generating approximately 2 ATP through oxidative phosphorylation. This traditional estimate aligns with standard biology textbooks and MCQs for exams like NEET.
Option Explanations
FADH2 enters the ETC after Complex I, bypassing one proton-pumping site, so it yields less ATP than NADH (typically 3 ATP).
| Option | Value | Explanation |
|---|---|---|
| 1 | 0.5 | Incorrect; too low, not matching any standard yield. |
| 2 | 1 | Incorrect; underestimates proton gradient from Complexes II-IV. |
| 3 | 1.5 | Modern estimate (~1.5 ATP) based on precise H+/ATP ratios, but exam contexts use 2. |
| 4 | 2 | Correct; classical value from ~6 protons pumped, ~4 protons per ATP. |
Process Overview
FADH2 from Krebs cycle donates electrons to Complex II, driving proton flow via Complexes III/IV and ATP synthase. This supports ~2 ATP, vital for total respiration yield calculations (e.g., ~32 ATP/glucose).
