Electron Transport Chain

What is the primary function of the electron transport chain in cellular respiration?

To convert high-energy electrons from NADH and FADH₂ into ATP via oxidative phosphorylation.

Where does the electron transport chain occur in eukaryotic cells?

In the inner mitochondrial membrane.

What is the final electron acceptor in the ETC?

Oxygen (O₂), which combines with electrons and protons to form water.

Which complex receives electrons from NADH?

Complex I (NADH dehydrogenase).

Which complex receives electrons from FADH₂?

Complex II (succinate dehydrogenase).

What is the role of Coenzyme Q (ubiquinone)?

It shuttles electrons from Complex I and II to Complex III.

What is the role of cytochrome c?

It transfers electrons from Complex III to Complex IV.

Which complexes pump protons into the intermembrane space?

Complexes I, III, and IV.

How does the ETC contribute to ATP synthesis?

It creates a proton gradient that powers ATP synthase via chemiosmosis.

How many ATP molecules are generated per NADH in the ETC?

Approximately 3 ATP.

How many ATP molecules are generated per FADH₂ in the ETC?

Approximately 2 ATP.

What is the total ATP yield from the ETC per glucose molecule?

About 26–28 ATP.

Why is oxygen essential for the ETC?

Without oxygen, electrons cannot be passed to the final acceptor, halting the chain and ATP production.

What happens if Complex IV is inhibited (e.g., by cyanide)?

Electron flow stops, ATP production ceases, and cells die rapidly.

How does the ETC in mitochondria compare to the one in chloroplasts?

Both use electron flow to build a proton gradient and drive ATP synthesis, but chloroplasts use light energy and produce NADPH instead of water.

What is the first step of the electron transport chain?

NADH donates electrons to Complex I (NADH dehydrogenase), initiating the chain and pumping H⁺ into the intermembrane space.

What happens at Complex II in the ETC?

FADH₂ donates electrons to Complex II (succinate dehydrogenase), but this complex does not pump protons.

What is the role of Coenzyme Q (ubiquinone)?

It shuttles electrons from Complexes I and II to Complex III.

What occurs at Complex III (cytochrome bc₁)?

Electrons are transferred to cytochrome c, and more H⁺ are pumped into the intermembrane space.

What is the function of cytochrome c in the ETC?

It acts as a mobile electron carrier between Complex III and Complex IV.

What happens at Complex IV (cytochrome c oxidase)?

Electrons are transferred to oxygen, forming water; H⁺ are pumped across the membrane.

Why is oxygen critical in the ETC?

It serves as the final electron acceptor, allowing the chain to continue and preventing backup of electrons.

What is the result of proton pumping during the ETC?

A proton gradient forms across the inner mitochondrial membrane.

How does ATP synthase use the proton gradient?

H⁺ flow back into the matrix through ATP synthase, driving the phosphorylation of ADP to ATP.

What is the total ATP yield from the ETC per glucose molecule?

Approximately 26–28 ATP, depending on shuttle efficiency and cell type.