NADH Oxidation

What is the main source of ATP production during cellular respiration?

The oxidation of NADH via the electron transport chain.

Why is oxygen essential in oxidative phosphorylation?

It acts as the final electron acceptor, forming water.

How are electrons from NADH transferred through the electron transport chain?

Via a series of membrane-bound redox enzymes.

What provides the driving force for the flow of electrons in the ETC?

The large difference in reduction potential between NADH and oxygen.

What role do protons play in ATP synthesis?

They form an electrochemical gradient across the inner mitochondrial membrane.

What is the chemiosmotic theory?

ATP is synthesized as protons flow back into the mitochondrial matrix down their electrochemical gradient.

What part of the mitochondria houses the electron transport chain proteins?

The inner mitochondrial membrane.

What two forces make up the proton motive force?

The proton gradient (ΔpH) and the membrane potential (Δψ).

What acts as the "battery" in the ETC electrical analogy?

The electron transport chain itself.

What is the function of ATP synthase in this system?

It converts the energy of the proton gradient into ATP.

How many ATPs are generated from glycolysis and the TCA cycle before oxidative phosphorylation?

Four (2 from glycolysis, 2 from the TCA cycle as GTP).

Where is most of the energy stored before oxidative phosphorylation?

In reduced electron carriers, mainly NADH and FADH₂.

How is redox energy used in the ETC?

To pump protons from the mitochondrial matrix to the intermembrane space.

What does the flow of electrons through ETC complexes cause?

Conformational changes that allow the complexes to pump protons.

What happens if the ETC is inhibited at any complex?

The entire chain shuts down and ATP production stops.

What are the two main types of mechanisms for proton pumping?

Redox loop and conformational proton pump.

Which ETC complex uses a redox loop mechanism?

Complex III.

What is the role of Complex I?

Oxidizes NADH and reduces coenzyme Q (ubiquinone), pumping 4 protons.

What cofactor in Complex I accepts electrons from NADH?

FMN (flavin mononucleotide).

What does coenzyme Q do?

It carries electrons from Complex I or II to Complex III.

What is the redox state transition of coenzyme Q?

Ubiquinone (oxidized) → semiquinone → ubiquinol (reduced).

Which complex is also part of the citric acid cycle?

Complex II (succinate dehydrogenase).

Does Complex II pump protons?

No, it only transfers electrons to coenzyme Q.

What does Complex III do?

Transfers electrons from QH₂ to cytochrome c and pumps 4 protons.

What is the Q cycle?

A mechanism in Complex III that transfers electrons and recycles coenzyme Q.

How many protons are pumped from NADH oxidation before ATP synthase?

10 protons (4 from Complex I, 4 from III, 2 from IV).

What small soluble protein carries electrons to Complex IV?

Cytochrome c.

What is the role of Complex IV?

Accepts electrons from cytochrome c, reduces O₂ to water, and pumps 2 protons.

What happens to the reduction potential at each step in the ETC?

It increases progressively to maximize reversible work.

What determines the direction of electron flow in the ETC?

The increasing positive E°’ (reduction potential) of successive carriers.

Why are small redox steps beneficial in the ETC?

They minimize energy lost as heat and maximize useful work.

How does the structure of mitochondria support oxidative phosphorylation?

Its inner membrane's large surface area allows for more ETC proteins.

What tissue has more mitochondria and why?

Dark (oxidative) muscle

What is the function of mitochondrial DNA?

It encodes proteins needed for ETC and other mitochondrial processes.

How many protons are required to make 1 ATP?

About 3.3 protons using ATP synthase with a 10-subunit c-ring.

What structure of ATP synthase synthesizes ATP?

The F₁ component, particularly the β subunits.

How does proton flow drive ATP production?

It rotates the γ subunit of ATP synthase, causing conformational changes in β subunits.

What are the three conformations of the β subunits in ATP synthase?

Loose (binds ADP + Pi), Tight (forms ATP), and Open (releases ATP).

How many ATP molecules are made per full rotation of ATP synthase?

Three ATP molecules per 360° turn.

What changes the binding affinity of ATP synthase for ATP?

The proton gradient alters the dissociation constant (Kd) of ATP binding.

What is the typical binding constant (Kd) of ATP without a gradient?

10⁻¹² M, meaning very tight binding.

What is the Kd of ATP with the gradient present?

10⁻⁶ M, allowing easier release of ATP.

How efficient is the ETC in converting redox energy into ATP?

About 94%.

How much energy is released by oxidation of NADH directly?

Approximately −220 kJ/mol.

How much energy is used to pump 10 protons per NADH?

About −208 kJ/mol.

What is the experimental evidence for ATP synthase rotation?

Actin filament or magnetic bead attached to γ subunit shows rotation under ATP hydrolysis.

What is the function of the stator in ATP synthase?

It prevents the headpiece from rotating with the rotor, allowing proper conformational changes.

How many protons are pumped per NADH oxidized in the ETC?

10 protons.

How many protons are needed to synthesize 1 ATP via ATP synthase?

Approximately 4 protons.

How many ATP molecules are produced per NADH?

2.5 ATP.

Why is the theoretical yield 2.5 ATP per NADH?

Because 10 protons are pumped per NADH and it takes ~4 protons per ATP.

Why can't NADH from glycolysis directly enter the mitochondria?

There is no NADH transporter in the inner mitochondrial membrane.

What is the purpose of NADH shuttles?

To transfer electrons from cytosolic NADH into the mitochondrial matrix for oxidative phosphorylation.

Which NADH shuttle is used in most tissues like the liver?

The malate-aspartate shuttle.

What is the first step of the malate-aspartate shuttle?

Cytosolic NADH reduces oxaloacetate to malate.

What happens to malate in the malate-aspartate shuttle?

It is transported into the mitochondrial matrix via an antiporter.

What is malate exchanged for during its mitochondrial transport?

Alpha-ketoglutarate.

What happens to malate inside the mitochondrial matrix?

It is oxidized back to oxaloacetate, producing NADH.

What happens to oxaloacetate after it's formed in the matrix?

It undergoes transamination to form aspartate.

What amino acid donates an amino group to oxaloacetate?

Glutamate, which becomes alpha-ketoglutarate.

What happens to aspartate in the malate-aspartate shuttle?

It is transported out of the mitochondria in exchange for glutamate.

What happens to aspartate in the cytoplasm?

It is deaminated back to oxaloacetate, completing the cycle.

How many enzymes and transporters are involved in the malate-aspartate shuttle?

Four enzymes and two transporters.

How many ATPs are earned per glucose when the malate-aspartate shuttle is used?

32 ATP.

Does the malate-aspartate shuttle consume ATP directly?

No, it transfers electrons without net energy expenditure.

Which tissue primarily uses the glycerol 3-phosphate shuttle?

Skeletal muscle.

Why does muscle use the glycerol 3-phosphate shuttle instead of malate-aspartate?

It is faster, supporting rapid ATP demand during contraction.

How many transporters and enzymes are involved in the glycerol 3-phosphate shuttle?

One transporter and two enzymes.

What substrate does cytosolic NADH reduce in the glycerol 3-phosphate shuttle?

Dihydroxyacetone phosphate (DHAP).

What is DHAP converted to in the glycerol 3-phosphate shuttle?

Glycerol 3-phosphate.

What happens to glycerol 3-phosphate inside mitochondria?

It reduces FAD to FADH₂.

Why does the glycerol 3-phosphate shuttle yield less ATP than malate-aspartate?

Because it generates FADH₂, which only pumps 6 protons, yielding 1.5 ATP per molecule.

How many ATPs are earned per glucose when the glycerol 3-phosphate shuttle is used?

30 ATP.

What happens to the DHAP after glycerol 3-phosphate is oxidized?

It is transported back to the cytosol to continue the cycle.