Mitochondrial Electron Transport Chain and Oxidative Phosphorylation

What is the primary function of the electron transport chain (ETC)?

To generate ATP through oxidative phosphorylation by transferring electrons from reduced cofactors.

Where does oxidative phosphorylation occur within the cell?

In the mitochondrial matrix and at the inner mitochondrial membrane.

What are the names of the complexes involved in the electron transport chain?

Complexes I, II, III, and IV.

What is the role of ATP synthase in oxidative phosphorylation?

ATP synthase catalyzes the synthesis of ATP using the proton gradient established by the electron transport chain.

What is the pathway of electron flow in the electron transport chain?

Electrons flow from reduced cofactors (NADH, FADH2) to complexes I and II, then to coenzyme Q, complex III, cytochrome c, and finally to complex IV where they reduce oxygen to water.

What are the physiological effects of inhibitors of the electron transport chain?

They can block electron flow, leading to decreased ATP production and potential cellular damage.

What are uncoupling agents and their mechanism of action?

Uncoupling agents disrupt the proton gradient, causing energy to be released as heat instead of being used for ATP synthesis.

How many ATP molecules are produced when electrons from reduced cofactors are donated to the ETC?

Typically, about 2.5 ATP per NADH and 1.5 ATP per FADH2.

What vitamins and minerals are required for the electron transport chain?

Vitamins B2 (riboflavin), B3 (niacin), and minerals such as iron and copper.

What is the function of complex I in the electron transport chain?

Complex I oxidizes NADH, transferring electrons to coenzyme Q and pumping protons across the mitochondrial membrane.

What is the role of coenzyme Q in the electron transport chain?

Coenzyme Q transports electrons from complexes I and II to complex III.

What is the function of complex II in the electron transport chain?

Complex II oxidizes FADH2 and transfers electrons to coenzyme Q; it does not pump protons.

What happens at complex III in the electron transport chain?

Complex III transfers electrons from coenzyme Q to cytochrome c and pumps protons into the intermembrane space.

What is the final electron acceptor in the electron transport chain?

Molecular oxygen (O2).

What is produced as a result of the transfer of electrons to oxygen in complex IV?

Water (H2O).

What is the significance of cytochrome c in the electron transport chain?

Cytochrome c carries electrons from complex III to complex IV and is involved in apoptosis when released into the cytosol.

What is the role of proton pumps in the electron transport chain?

Proton pumps (complexes I, III, and IV) create a proton gradient across the inner mitochondrial membrane, which is used to generate ATP.

How does the malate-aspartate shuttle function?

It transports electrons from cytosolic NADH into the mitochondria, allowing for ATP production.

How does the glycerol 3-phosphate dehydrogenase shuttle work?

It transfers electrons from cytosolic NADH to FAD, forming FADH2, which then enters the electron transport chain.

What is the overall equation for the reduction of oxygen in the electron transport chain?

O2 + 4 e⁻ + 4 H⁺ → 2 H2O.

What is the importance of the proton gradient established by the electron transport chain?

It drives ATP synthesis through ATP synthase during oxidative phosphorylation.

What is the role of complex IV in the electron transport chain?

Complex IV transfers electrons from cytochrome c to oxygen, producing water and pumping protons.

What is the relationship between oxidative phosphorylation and cellular respiration?

Oxidative phosphorylation is the final step of cellular respiration, where ATP is produced using energy from the electron transport chain.

What drives ATP synthesis in mitochondria?

The spontaneous passage of protons through the ATP synthase complex.

What is the role of the ATP synthase complex?

It couples the electrochemical gradient to ATP synthesis.

What are the major components of ATP synthase?

FO pore, c subunits, A and B subunits, g subunit, and F1 headpiece.

What is the function of the c subunits in ATP synthase?

They form a protein rotor that rotates as protons bind and enter the mitochondrial matrix.

How do ADP and ATP exchange across the mitochondrial membrane?

Through ADP/ATP translocases (AAC and ANT).

What triggers the activity of ADP/ATP translocase?

When ADP accumulates in the cytosol and ATP accumulates in the mitochondria.

How does NADH from glycolysis enter the mitochondria?

Through the Glycerol 3-Phosphate Shuttle or the Malate-Aspartate Shuttle.

What is the Glycerol 3-Phosphate Shuttle?

A faster but less efficient mechanism to transport electrons from NADH into the mitochondria.

What is the Malate-Aspartate Shuttle?

A more efficient but slower mechanism for transporting NADH into the mitochondria.

What happens to NADH during the Glycerol 3-Phosphate Shuttle?

It is converted back to NAD+ while producing FADH2.

What is the net ATP production from the Malate-Aspartate Shuttle?

About 3 ATP molecules by oxidative phosphorylation.

What are the consequences of blocking the electron transport chain (ETC)?

Accumulation of NADH and FADH2, reduced ATP synthesis, and diminished oxygen demand.

Name one common inhibitor of the electron transport chain.

Cyanide.

What is the role of high-energy electrons in oxidative phosphorylation?

They create a hydrogen ion gradient that drives ATP synthesis.

What is the significance of the proton gradient in mitochondria?

It is essential for ATP production via ATP synthase.

What happens to ATP produced in the mitochondrial matrix?

It is transported to the cytoplasm via ADP/ATP translocases.

What is the function of the g subunit in ATP synthase?

It connects the FO pore to the F1 headpiece and rotates due to the c subunits.

What is the role of the ab subunits in the F1 headpiece?

They bind ADP and Pi and catalyze the formation of ATP using mechanical energy.

What is produced when electrons bind to oxygen in the electron transport chain?

Water.

What is the primary energy currency of the cell?

ATP.

How does the concentration of protons affect ATP synthesis?

High proton concentration in the intermembrane space drives ATP synthesis.

What is the main function of the inner mitochondrial membrane?

It houses the components of the electron transport chain and ATP synthase.

What is oxidative phosphorylation?

The process of ATP production using the electron transport chain and chemiosmosis.

What is the role of oxygen in cellular respiration?

It acts as the final electron acceptor in the electron transport chain.

What happens to newly produced ATP in the mitochondrial matrix?

It falls off into the matrix and is available for use by the cell.

What is the importance of the hydrogen ion gradient in ATP synthesis?

It provides the energy needed for ATP synthase to produce ATP.

What substances block the electron transport chain (ETC) between NADH dehydrogenase and CoQ?

Amytal and Rotenone

How do Amytal and Rotenone affect NADH?

They prevent the utilization of NADH as a substrate.

Which complex in the ETC is affected by Antimycin A?

Complex III

What is the result of cyanide binding to cytochrome c oxidase?

It results in a complete shut-off of electron flow in the ETC.

What are azides used for?

As gas-producing materials in airbags, chemical preservatives, pest-control materials, and in certain drugs.

What is uncoupling in the context of the electron transport chain?

When protons leak back into the mitochondrial matrix without passing through ATP synthase, leading to heat production instead of ATP synthesis.

What is Thermogenin?

A natural uncoupling protein responsible for producing body heat.

What is DNP and why is it significant?

DNP (2,4-dinitrophenol) is a chemical uncoupler that was used as a weight loss aid but is banned due to its toxicity.

What does oligomycin inhibit?

ATP synthase

How does metformin affect the mitochondrial respiratory chain?

It inhibits complex I, decreasing NADH oxidation and ATP synthesis.

What are typical symptoms of chemical uncoupling agents?

Elevation of body temperature, labored respiration, and potential for death.

What is the primary source of body heat in humans?

Brown adipose tissue (brown fat) through uncoupled mitochondria.

What role does creatine phosphate play in muscle contraction?

It quickly supplies ATP for the first few seconds of muscle contraction.

What happens during substrate-level phosphorylation?

ADP is converted to ATP directly through a substrate without the use of the electron transport chain.

What is the role of adenylate kinase in low energy states?

It converts ADP + ADP into ATP + AMP.

What were the side effects of dinitrophenol when prescribed as a weight-reducing agent?

Sweating and slight elevation in temperature, which could lead to fatal overheating in some patients.

What symptoms did workers exposed to trinitrophenol experience?

Elevated temperature, weakness, and accelerated breathing.