Electron Transport Chain + Oxidative Phosphorylation

Explain the biological purpose of the electron transport chain

Transfers electrons from NADH/FADH₂ to O₂ while pumping protons to build proton-motive force

Explain the biological purpose of oxidative phosphorylation

Uses proton-motive force to synthesize ATP from ADP and Pi

Explain why ETC and oxidative phosphorylation are separate but coupled processes

ETC generates proton gradient; ATP synthase uses it to make ATP

Explain why electrons flow spontaneously through the ETC

Move from lower to higher reduction potential carriers toward O₂

Explain why oxygen is the terminal electron acceptor

Highest reduction potential; forms stable H₂O

Explain why ETC stops when oxygen is absent

Electrons cannot be passed off; carriers remain reduced

Explain the reaction catalyzed by Complex I

NADH transfers electrons to ubiquinone while protons are pumped

Explain the role of FMN in Complex I

Accepts two electrons from NADH

Explain the role of iron–sulfur clusters in Complex I

Transfer single electrons stepwise

Explain how proton pumping occurs in Complex I

Electron transfer induces conformational changes that move protons

Explain why Complex I is a major regulatory entry point

Handles most cellular NADH

Explain the reaction catalyzed by Complex II

Succinate → fumarate; electrons transferred to ubiquinone

Explain why Complex II does not pump protons

Insufficient free energy from succinate oxidation

Explain why FAD is used instead of NAD⁺ in Complex II

Succinate oxidation potential too low for NAD⁺ reduction

Explain why Complex II is part of both TCA and ETC

Catalyzes TCA reaction and feeds electrons into ETC

Explain the role of ubiquinone in the ETC

Mobile lipid-soluble electron carrier

Explain why ubiquinone can carry both electrons and protons

Can exist in oxidized, semiquinone, and reduced forms

Explain why ubiquinone is essential for ETC flexibility

Accepts electrons from multiple complexes

Explain the reaction catalyzed by Complex III

Transfers electrons from ubiquinol to cytochrome c

Explain the Q cycle

Mechanism that couples electron transfer to proton translocation

Explain why the Q cycle amplifies proton pumping

Two electrons result in four protons released

Explain the role of cytochrome b and c₁

Sequential electron transfer via heme groups

Explain the role of cytochrome c

Mobile protein that transfers electrons to Complex IV

Explain why cytochrome c carries only one electron

Heme iron cycles between Fe²⁺ and Fe³⁺

Explain the reaction catalyzed by Complex IV

Electrons reduce O₂ to H₂O

Explain why Complex IV is the most tightly regulated complex

Controls oxygen consumption

Explain the role of copper and heme centers in Complex IV

Facilitate electron transfer and oxygen reduction

Explain how proton pumping occurs in Complex IV

Electron transfer drives conformational proton movement

Explain what the proton-motive force consists of

Membrane potential (Δψ) + proton gradient (ΔpH)

Explain why proton pumping stores energy

Creates electrochemical gradient across membrane

Explain why inner mitochondrial membrane must be impermeable to protons

Prevents energy dissipation

Explain the structure of ATP synthase

F₀ proton channel + F₁ catalytic head

Explain the binding-change mechanism

Rotation forces β subunits through loose, tight, open states

Explain how proton flow drives ATP synthesis

Proton movement rotates c-ring and γ shaft

Explain why ATP synthesis does not require a phosphorylated intermediate

Mechanical energy drives ATP formation

Explain why ATP synthase is reversible

Can hydrolyze ATP to pump protons if gradient collapses

Explain what coupling means in oxidative phosphorylation

Electron transport linked to ATP synthesis via proton gradient

Explain respiratory control by ADP

High ADP increases ETC rate; low ADP slows ETC

Explain why ETC slows when ATP demand is low

Proton gradient builds and resists pumping

Explain why oxidative phosphorylation controls ETC rate

ETC activity depends on proton gradient usage

Explain what uncoupling is

Proton gradient dissipated without ATP synthesis

Explain how chemical uncouplers work

Carry protons across membrane, bypassing ATP synthase

Explain the effect of uncoupling on oxygen consumption

Oxygen consumption increases

Explain the effect of uncoupling on ATP production

ATP synthesis decreases

Explain why uncoupling produces heat

Energy released as thermal motion

Explain how cyanide inhibits oxidative phosphorylation

Binds Complex IV; blocks oxygen reduction

Explain how rotenone inhibits the ETC

Blocks electron transfer in Complex I

Explain how antimycin A inhibits the ETC

Blocks electron transfer in Complex III

Explain how oligomycin inhibits ATP synthesis

Blocks F₀ proton channel

Explain what happens to proton gradient when ATP synthase is inhibited

Gradient increases; ETC slows

Explain how superoxide is formed in the ETC

Electron leakage to oxygen at Complex I or III

Explain why excessive ROS is dangerous

Damages proteins, lipids, and DNA

Explain the ATP yield per NADH

Approximately 2.5 ATP

Explain the ATP yield per FADH₂

Approximately 1.5 ATP

Explain why FADH₂ yields less ATP than NADH

Bypasses proton-pumping Complex I

Explain how the ETC links to glycolysis and TCA

Uses NADH/FADH₂ produced upstream

Explain why ETC activity influences TCA cycle rate

Controls NAD⁺ availability

Explain why ETC inhibition affects gluconeogenesis

High NADH inhibits gluconeogenic enzymes

Explain everything you know about ETC and oxidative phosphorylation

ETC transfers electrons to oxygen, builds proton gradient, ATP synthase uses gradient to make ATP; tightly regulated by ADP and oxygen

Explain ETC and oxidative phosphorylation in the context of whole-body metabolism

Primary ATP source in aerobic tissues; integrates with all fuel pathways

Summarize ETC and oxidative phosphorylation in one sentence

A coupled system where electron transfer to oxygen drives proton pumping, which powers ATP synthesis via ATP synthas