Lecture 16 Electron Transport System and Oxidative Phosphorylation

What is the primary function of mitochondria in eukaryotic aerobic metabolism?

Mitochondria host the citric acid cycle, fatty acid β-oxidation, amino acid oxidation, thermogenesis, steroid synthesis, apoptosis, and ATP production.

What is the final electron acceptor in the electron transport chain (ETC)?

Molecular oxygen (O₂), which is reduced to form H₂O.

How is the energy from the electron flow in the ETC used?

It is used to transport protons across a proton-impermeable membrane, creating an electrochemical gradient.

What drives ATP synthesis in the mitochondria?

The flow of protons down their electrochemical gradient through ATP synthase.

What are the five types of electron-carrying molecules in the respiratory chain?

NAD, flavoproteins, ubiquinone (coenzyme Q), cytochromes, and iron-sulfur proteins.

What is the Chemiosmotic Theory?

It states that the transmembrane proton gradient serves as the energy reservoir for ATP synthesis during oxidative phosphorylation.

What is the role of Complex I in the electron transport chain?

Complex I transfers electrons from NADH to ubiquinone, facilitating proton pumping.

What is the function of ATP synthase in the mitochondria?

It couples proton flow to the phosphorylation of ADP, synthesizing ATP.

What regulates oxidative phosphorylation?

The availability of ADP, which controls the rate of electron transfer, ATP synthesis, and overall cellular respiration.

What is the consequence of uncoupling mitochondria in brown adipose tissue (BAT)?

It leads to the dissipation of energy as heat, contributing to thermogenesis.

What are the two mitochondrial shuttle systems for NADH?

The malate-aspartate shuttle and the glycerol 3-phosphate shuttle.

What causes Myoclonic Epilepsy with Ragged-Red Fibers (MERRF) Syndrome?

A mutation in the gene encoding a tRNA specific for lysine, affecting mitochondrial function in skeletal muscles.

What is mitochondrial donation, and what ethical issues does it raise?

It is the transplantation of a mother's nuclear DNA into an ovum with healthy mitochondria, raising ethical concerns about genetic manipulation.

How do defects in mitochondrial DNA contribute to disease?

Mutations in mtDNA can cause diseases like Leber hereditary optic neuropathy (LHON) and MERRF, affecting brain and muscle function.

What is the role of the inner mitochondrial membrane in oxidative phosphorylation?

It is impermeable to most small molecules and ions, requiring specific transporters, and houses the proteins of the electron transport chain.

What are mitochondrial cristae and their function?

Cristae are convolutions in the inner mitochondrial membrane that increase surface area, enhancing the capacity for ATP production in metabolically active cells.

What are the three types of electron transfers in oxidative phosphorylation?

1. Direct electron transfer, 2. Transfer as a hydrogen atom (H⁺ + e⁻), 3. Transfer as a hydride ion (⁻).

How do flavoproteins contribute to electron transfer?

Flavoproteins contain FMN or FAD, which accept electrons and have a higher E° (electrical potential) than the compound being oxidized, driving electron flow.

What is the function of ubiquinone (coenzyme Q) in the respiratory chain?

Ubiquinone accepts electrons, diffuses through the inner mitochondrial membrane, and plays a key role in coupling electron flow to proton movement.

What is the role of cytochromes in the electron transport chain?

Cytochromes carry electrons, with iron-containing heme groups absorbing visible light and transferring electrons between complexes.

Describe the function of Complex II in the electron transport chain.

Complex II transfers electrons from succinate to ubiquinone (Q), but unlike Complex I, it does not pump protons across the membrane.

What happens during the Q cycle in Complex III?

The Q cycle transfers electrons from ubiquinol to cytochrome c while pumping protons into the intermembrane space.

What is the final step in electron transport in Complex IV?

Complex IV carries electrons from cytochrome c to molecular oxygen (O₂), reducing it to water (H₂O) and contributing to proton pumping.

What are respirasomes, and what is their function?

Respirasomes are supercomplexes of electron transport chain complexes I, III, and IV that facilitate electron transfer and limit the production of reactive oxygen species (ROS).

What is the proton-motive force?

It is the energy stored in the electrochemical proton gradient across the inner mitochondrial membrane, driving ATP synthesis.

What is rotational catalysis in ATP synthase?

Rotational catalysis is the process by which the flow of protons through ATP synthase causes rotation of the c ring, leading to ATP synthesis.

How does the malate-aspartate shuttle function?

The malate-aspartate shuttle transfers NADH equivalents into the mitochondria, where they enter the respiratory chain at Complex I.

What is the function of uncoupling protein 1 (UCP1) in brown adipose tissue (BAT)?

UCP1 allows protons to return to the mitochondrial matrix without generating ATP, dissipating energy as heat and contributing to thermogenesis.

What are mitochondrial encephalomyopathies?

These are genetic diseases affecting mitochondria, primarily impacting the brain and skeletal muscle, often inherited maternally.

What causes Leber hereditary optic neuropathy (LHON)?

LHON is caused by mutations in mitochondrial DNA affecting Complex I of the electron transport chain, leading to central vision loss.

What does it mean for ADP to be the "acceptor control" of cellular respiration?

Oxygen consumption depends on ADP.
-The rate of O2 consumption depends on the availability of ADP, the Pi acceptor.

What is mitochondrial thermogenesis?

energy oxidation being dissipated as heat caused by uncoupling protein 1 providing a path for protons to return to the matrix without passing through the F0F1 complex.
-Brown adipose tissue (BAT) is adipose tissue in newborn mammals that functions to generate heat through fuel oxidation

Who do you inherit mitochondrial DNA from?

mother