Oxidative Phosphorylation

What do the electron transport and oxidative phosphorylation do?

capture the energy in the redox potential of NADH and FADH2

What does coupling depend on

the electrochemical gradient created by proton pumping across the inner mitochondrial membrane.

What is the energy from glucose used to produce?

ATP

What does the electron transport do

It transfers electrons through a series of complexes, generating a proton gradient.

What does Oxidative Phosphorylation do?

the proton gradient runs downhill to drive the synthesis of ATP

What is the ultimate electron acceptor

Oxygen

What happens the more positive reduction happens?

the more the compound wants electrons

What determines the direction of electron flow in the ETC?

Electrons flow from carriers with low to high standard reduction potential (E°’)—from NADH to O₂, which has the highest E°

How many complexes is the electron transport chain made off?

4

What does complex 1 named

NADH dehydrogenase

What does complex 2 named

Succinate dehydrogenase

What does complex 3 named

Ubiquinone Cytochrome c oxidoreductase

What does complex 4 named

Cytochrome c oxidase

What does coenzyme Q do?

Lipid-soluble electron carrier; transfers electrons from Complex I/II → Complex III (helps keep things moving)​

Where is coezyme Q located

Mitrochondria Membrane

What is the role of cytochrome c?

Small, mobile heme protein that transfers electrons from Complex III → Complex IV​.

What does not happen in complex 2

no proton pumping occurs during electron transport.

How many Hydrogens make one ATP

around 3

What are the net gains of the ETC

The net gains of the electron transport chain (ETC) include approximately 28 to 30 ATP molecules, water as a byproduct, and the reduction of oxygen.

What ETC inhibitor blocks electron flow from NADH to ubiquinone (Q) at Complex I?

Rotenone , Stops electron transfer before Q; no proton pumping at Complex I.

Which ETC inhibitor blocks electron flow from cytochrome b to cytochrome c₁ at Complex III?

Antimycin A, Causes Cyt b to stay reduced, downstream cytochromes remain oxidized.

Which inhibitors block Complex IV by preventing electron transfer to oxygen?

Cyanide (CN⁻), Carbon monoxide (CO), and Azide; Stop final electron transfer → O₂ can’t be reduced → ETC backs up.

What happens upstream of an ETC inhibitor block?

Electron carriers become reduced (can’t pass electrons downstream).

What happens downstream of an ETC inhibitor block?

Electron carriers remain oxidized (they don’t receive electrons).

What is ATP synthase (Complex V)?

A multisubunit transmembrane protein (~450 kDa) responsible for synthesizing ATP using the proton gradient across the inner mitochondrial membrane.

What are the two major components of ATP synthase?

• F₀: water-insoluble, membrane-embedded proton pore

• F₁: water-soluble peripheral protein complex that performs ATP synthesis.

What is the role of the F₀ unit?

It forms a channel that allows H⁺ ions to flow from the intermembrane space into the matrix, driven by the proton-motive force.

What is the role of the F₁ unit?

It uses the energy from proton flow (via rotation of γ subunit) to catalyze the synthesis of ATP from ADP + Pi in the matrix.

What forms the F0?

C-subunits (kinda looks like a flower")

What does the β-ADP conformation do?

It is not catalytically active, but binds ADP and Pi.

What does the β-ATP conformation do?

It is catalytically active and binds ATP.

What is the role of the β-Empty conformation?

It has low affinity for ATP or ADP and facilitates release of ATP.

What is the binding change mechanism in ATP synthase?

As the γ subunit rotates, each β subunit sequentially shifts through the β-ADP → β-ATP → β-Empty states to synthesize and release ATP.

How many protons are required for a 120° rotation of the γ subunit?

3 H⁺ protons are required per 120° turn

What subunits form the rotor that spins in ATP synthase?

The c-ring (in F₀) and γ subunit (in F₁).

What happens during conversion of β-ADP → β-ATP?

Synthesis of ATP from ADP and Pi occurs.

What happens during conversion of β-ATP → β-Empty?

ATP is released from the enzyme.

What is a natural biological example of ETC uncoupling?

Brown fat in hibernating mammals and newborns, where a protein called thermogenin (UCP1) allows protons to bypass ATP synthase​

Why is uncoupling useful in hibernating mammals or newborns?

It allows heat generation (non-shivering thermogenesis) to maintain body temperature in the cold without muscle activity

What is thermogenin (UCP1) and what does it do?

A proton channel in brown adipose tissue that dissipates the proton gradient, producing heat instead of ATP.

What’s the key conclusion from these experiments?

Electron transport and ATP synthesis are normally coupled, but uncouplers like DNP prove they can be functionally separated.

What blocks ATP Synthase?

Venturicidin & Oligomycin

Electron transport can be…

uncoupled from ATP Synthesis

How can the electron transport be uncoupled from ATP synthesis?

using DNP

Can you have ETC without ATP synthesis?

True

What does DNP do

Can carry H+ across inner mitochondrial membrane

When it is uncoupled what is released instead of ATP?

Heat

What protein allows protons to flow down a gradient

Thermogenin