Electrons from FADH2 generated inside mitochondria yield approximately 1.5 ATP each, whereas electrons from NADH yield approximately 2.5 ATP. The reason for this difference is:

• A FAD-linked substrates deliver electrons to ubiquinone, bypassing complex I and its proton-pumping step ✓
• B FADH2 carries electrons with lower reducing potential, so fewer protons are pumped at complex III
• C FADH2 donates only one electron per molecule whereas NADH donates two
• D FADH2 oxidation does not involve cytochrome c

Explanation

NADH passes its electrons to complex I, which pumps four protons across the inner membrane before transferring them to ubiquinone. FAD-linked substrates such as succinate hand electrons directly to ubiquinone via complex II, which pumps no protons, so those electrons traverse only complexes III and IV. Both carriers donate two electrons and both routes pass through complex III, cytochrome c, and complex IV, eliminating options C and D. The difference lies entirely in skipping the complex I pumping step.

Reference: Lehninger Principles of Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.