Question

Electrons taking part in electron transport system inside mitochondria come from

• A. Pyruvate
• B. NADH $\left(H^{+}\right)$
• C. $FAD{H}_2$
• D. Both B and C

Answer 1

The correct option is D Both B and C

Electron transport chain is a series of proteins and organic molecules found in the inner membrane of mitochondria. Electrons are passed from one member of transport chain to another in a series of redox reactions. All the electrons that enter the transport chain come from NADH and FADH2 molecules produced during glycolysis, pyruvate oxidation and citric acid cycle. NADH is very good at donating electrons as its electrons are at the high energy level and thus it can transfer its electrons directly to complex I turning back into NAD. As the electrons move through complex I in a series of reactions, the energy is released and this energy is used to pump protons from the matrix into intermembrane space. FADH2 is less efficient in donating electrons as its electrons are at the low energy level and so it cannot transfer its electrons directly to complex I. Instead it transfers them through complex II which does not pump protons across the membrane.

Thus, the correct answer is option D.