Electron Transport & Oxidative Phosphorylation (Garrett & Grisham Ch 21)

Question-and-answer flashcards covering key concepts of electron transport, oxidative phosphorylation, ATP synthase, inhibitors, uncouplers, P/O ratios, and shuttle systems as presented in Garrett & Grisham Chapter 21.

Where in the cell do electron transport and oxidative phosphorylation occur?

At and within the inner mitochondrial membrane.

What is the overall purpose of electron transport?

To pass electrons from reduced coenzymes through a chain of proteins/coenzymes and create a proton gradient across the inner mitochondrial membrane.

What drives ATP synthesis in oxidative phosphorylation?

The downhill flow of protons back into the mitochondrial matrix through ATP synthase (chemiosmotic coupling).

Write the equation that relates free-energy change to reduction potential change.

ΔG°′ = –nF ΔE°′, where n = electrons transferred and F = Faraday’s constant.

How is ΔE°′ calculated for a redox pair?

ΔE°′ = E°′(acceptor) – E°′(donor).

In terms of reduction potential, from which half-reaction to which do electrons flow?

From the half-reaction with the more negative E°′ to the one with the more positive E°′.

Name the four major protein complexes of the respiratory chain.

Complex I (NADH-CoQ reductase), Complex II (succinate-CoQ reductase), Complex III (CoQ-cytochrome c reductase), Complex IV (cytochrome c oxidase).

What two mobile electron carriers shuttle between the complexes?

Coenzyme Q (ubiquinone, lipid-soluble) and cytochrome c (water-soluble).

Which complex accepts electrons directly from NADH?

Complex I (NADH-CoQ reductase).

Outline the electron path within Complex I.

NADH → FMN → several Fe-S centers → CoQ (ubiquinone).

How many protons are pumped across the membrane by Complex I per 2 electrons?

Four protons are pumped from matrix to intermembrane space.

Which TCA-cycle enzyme doubles as Complex II?

Succinate dehydrogenase.

Does Complex II pump protons?

No, Complex II does not translocate protons.

Give the net reaction catalyzed by Complex II.

Succinate + CoQ → fumarate + CoQH₂.

What redox cycle operates in Complex III?

The Q-cycle.

Name the principal transmembrane protein of Complex III and its hemes.

Cytochrome b with hemes bL and bH.

What is the lipid-soluble electron carrier in the Q-cycle?

UQH₂ (ubiquinol).

What is the water-soluble electron carrier that accepts electrons from Complex III?

Cytochrome c.

What is the terminal electron acceptor in the respiratory chain?

Molecular oxygen (O₂).

Which complex reduces O₂ to H₂O?

Complex IV (cytochrome c oxidase).

How many electrons are required to reduce one O₂ to two H₂O?

Four electrons.

List the metal centers found in cytochrome c oxidase.

Two hemes (a and a₃) and two copper sites (CuA and CuB).

Who proposed the chemiosmotic hypothesis?

Peter Mitchell.

What Nobel-recognized mechanism explains ATP synthase catalysis?

Paul Boyer’s binding-change mechanism.

Name the two structural parts of ATP synthase.

F₀ (proton channel) and F₁ (catalytic headpiece).

What experiment by Racker & Stoeckenius supported chemiosmosis?

Reconstitution of vesicles containing bacteriorhodopsin and ATP synthase; light-driven proton pumping produced ATP.

Which inhibitor blocks proton flow through ATP synthase?

Oligomycin (also DCCD).

Name an inhibitor of Complex I used as fish poison by Amazon natives.

Rotenone.

Which poisons inhibit Complex IV by binding to the ferric form of cytochrome a₃?

Cyanide, azide, and carbon monoxide.

What do uncouplers such as DNP or FCCP do?

They dissipate the proton gradient by shuttling protons across the membrane, uncoupling electron transport from ATP synthesis.

What charge movement is associated with the ATP-ADP translocase?

Export of ATP⁴⁻ and import of ADP³⁻ equals net movement of one negative charge out (equivalent to one H⁺ in).

Including export, how many protons are required per ATP synthesized?

Approximately four protons (≈3 for synthesis + 1 for export via translocase).

How many protons are pumped per electron pair from NADH to O₂?

Ten protons.

Calculate the P/O ratio for NADH oxidation.

10 H⁺ pumped / 4 H⁺ per ATP ≈ 2.5 ATP per NADH.

Calculate the P/O ratio for succinate (FADH₂) oxidation.

6 H⁺ pumped / 4 H⁺ per ATP ≈ 1.5 ATP per FADH₂.

Which shuttle transfers cytosolic NADH electrons to mitochondrial FAD, yielding 1.5 ATP/NADH?

The glycerophosphate shuttle.

Which shuttle transfers cytosolic NADH electrons to mitochondrial NAD⁺, yielding 2.5 ATP/NADH?

The malate-aspartate shuttle.

How many ATP are produced per glucose when the glycerol-3-phosphate shuttle operates?

About 30 ATP.

How many ATP are produced per glucose when the malate-aspartate shuttle operates?

About 32 ATP.

What structural feature makes uncouplers able to carry protons through the membrane?

They are hydrophobic molecules with a dissociable (acidic) proton that can pick up and release H⁺.

Which complex has an FMN as its initial electron acceptor?

Complex I (NADH-CoQ reductase).

What kind of clusters mediate one-electron transfers in complexes I–III?

Iron-sulfur (Fe-S) clusters.

Which lipid-soluble quinone cycles between oxidized (Q) and reduced (QH₂) forms?

Coenzyme Q (ubiquinone/ubiquinol).

What distinguishes heme c from heme b and heme a?

Heme c is covalently attached to its protein via thioether bonds to Cys residues (e.g., cytochrome c).