What can the electrons carried by NADH and FADH2 do?

• A. They can be moved between proteins in the inner membrane of the mitochondrion
• B. They can be used to synthesize NAD+
• C. They remain stored in the cytosol
• D. They are used for glycolysis directly

Answer: (A)

Electrons from NADH and FADH2 are transferred through the electron transport chain located in the inner mitochondrial membrane. As these electrons move from one protein complex to the next, energy is released at each step and used to pump protons across the membrane, creating a gradient. That gradient then drives ATP synthase to produce ATP from ADP and phosphate. In the process, NADH and FADH2 are oxidized to NAD+ and FAD, so they are recycled for reuse. They aren’t stored in the cytosol, they aren’t used directly in glycolysis, and their main role isn’t to synthesize NAD+, but to fuel the chain that ultimately makes most of the cell’s ATP.