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In mitochondrial electron transport, what is the direct role of o2?
- To function as the final electron acceptor in the electron transport chain.
- To oxidize NADH and FADH2 from glycolysis, acetyl CoA formation, and the citric acid cycle.
- To provide the driving force for the synthesis of ATP from ADP and Pi.
- To provide the driving force for the production of a proton gradient.
The correct answer about mitochondrial electron transport is below.
Electron transfer chain
The electron transfer chain (ETC) is an electron transfer system consisting of a series of electron carriers in an order of increasing affinity for electrons. All components are embedded in the inner mitochondrial membrane or in chloroplast vesicle membranes or other biological membranes.
All components are embedded in mitochondrial endosomes, chloroplast-like vesicle membranes, or other biological membranes, and formed into separate complexes in sequential segments. The physical arrangement of the carrier components within the complex is also consistent with the direction of electron flow.
The mitochondrial electron transport chain is accompanied by the oxidative exergy of nutrients and is also called the respiratory chain.
The main components of the electron transport chain in mitochondria include:
They are all hydrophobic molecules. All the components are proteins except ubiquinone. They transfer electrons through the reversible redox of their cofactors.
They form four complexes on the membrane surface, called complex I (NADP dehydrogenase complex), complex II (succinate dehydrogenase complex), complex III (cytochrome reductase complex), and complex IV (cytochrome oxidase complex).
NADH passes through complex I, coenzyme Q, complex III, cytochrome C, and complex IV in order to transfer electrons to oxygen and to discharge protons to the mitochondrial membrane gap to produce 2.5 ATP via mitochondrial ATP synthase.
FADH2 passes through complex II, coenzyme Q, complex III, cytochrome C, and complex IV to finally transfer electrons to oxygen and discharge protons to the mitochondrial membrane gap to finally generate 1.5 ATP via mitochondrial ATP synthase.
Since the former produces more ATP than the latter, the former is called the primary electron transport chain and the latter is called the secondary electron transport chain
The substances that accept and provide electrons or hydrogen (consisting of protons and electrons) within the mitochondrial electron transport system (respiratory chain) are called electron carriers.
They are coenzymes of various dehydrogenases, such as NAD+, FMN, FAD, ubiquinone, various cytochromes, etc. In the mitochondrial inner membrane, the hydrogen and electrons are sequentially arranged into chains according to their redox potentials, and the hydrogen and electrons shed by metabolites are passed to oxygen molecules to produce water, completing the bio-oxidation of metabolites.
Mitochondria play a role in eukaryotic electron transfer and oxidative phosphorylation by coupling the two reactions and providing enzymes and transporters for both
What does uncoupling of mitochondrial oxidative phosphorylation refer to?
In intact mitochondria, electron transfer and phosphorylation are tightly coupled. When the two processes, electron transfer, and ATP formation, are separated by the use of certain reagents, and only electron transfer but not ATP formation takes place, the effect is called uncoupling.
The reagent that can cause uncoupling is called an uncoupling agent. The essence of uncoupling is that the uncoupling agent eliminates the concentration or potential gradient of transmembrane protons generated in electron transfer. Only electron transfer without ATP is produced.
A typical uncoupling agent is the chemical 2,4-dinitrophenol (DNP), which is weakly acidic.
DNP is weakly acidic and can bind H or release H at different pH environments. DNP is also lipid-soluble and can transfer H from the outer side of the inner mitochondrial membrane to the inner side through the phospholipid bilayer, thus eliminating the H gradient.
In addition, ion carriers, such as valinomycin, an antimicrobial agent produced by streptomycin, are lipid-soluble and can ligand-bind to K ions, allowing K outside the mitochondrial membrane to be transferred to the inside, thus eliminating the transmembrane potential gradient.
There are also natural uncoupling proteins present in the inner mitochondrial membrane of some living cells. This protein constitutes a proton channel that allows extra-membrane protons to return to the membrane through its channel, eliminating the proton concentration gradient across the membrane and preventing the production of ATP to generate heat to increase body temperature.
Uncoupling agents are different from electron transport inhibitors. Uncoupling agents only eliminate the proton or potential gradient on both sides of the inner membrane, do not inhibit electron transfer in the respiratory chain, and even accelerate electron transfer and promote the consumption of respiratory substrates and molecular oxygen. However, no ATP is formed and only heat is produced.