Biochemistry of Electron Transport Chain

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Questions and Answers

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

It synthesizes ATP directly from succinate oxidation.

It transports electrons to molecular oxygen.

It pumps protons across the membrane.

It couples the oxidation of succinate with the reduction of ubiquinone. (correct)

Which reactive oxygen species is not produced by the electron leakage from Complex II?

Hydrogen peroxide (H2O2)

Superoxide radical

Hydroxyl radical (correct)

Singlet oxygen

Which electron carrier is directly affected if Pro is substituted for Cys in succinate dehydrogenase?

Cytochrome c

Iron-sulfur center (correct)

Ubiquinone

Flavin adenine dinucleotide (FAD)

What is the significance of oxygen's appearance in the atmosphere for complex life forms?

It made possible the evolution of oxidative phosphorylation. Signup and view all the answers

What occurs during the downhill electron flow in the electron transport chain?

Electrons move from oxidizable substrates to a final acceptor with a high reduction potential. Signup and view all the answers

Which enzyme is specifically linked to the fatty acid β-oxidation pathway in the mitochondrial matrix?

Acyl-CoA dehydrogenase Signup and view all the answers

What is the main role of the inner mitochondrial membrane?

Regulating the transport of specific molecules and ions Signup and view all the answers

Which of the following best describes the cristae of mitochondria?

The convolutions in the inner membrane which increase surface area Signup and view all the answers

Which process does NOT occur in the mitochondria?

Glycolysis Signup and view all the answers

What does the chemiosmotic theory primarily explain?

The production of ATP through proton gradients across membranes Signup and view all the answers

Which of the following is true regarding lactate dehydrogenase?

It is located in the cytosol and is involved in glycolysis. Signup and view all the answers

What is NOT a function of mitochondria?

Photosynthesis Signup and view all the answers

Which statement about the outer mitochondrial membrane is true?

Transport through it occurs via porins. Signup and view all the answers

What is the primary role of coenzyme A in metabolic pathways?

Facilitating metabolic functions in anabolic and catabolic pathways Signup and view all the answers

Which method involves measuring the oxidation rate of electron carriers upon reintroduction of O2?

Omitting O2 to reduce the entire chain Signup and view all the answers

Which electron carrier has the highest standard reduction potential among those listed?

½ O2 Signup and view all the answers

In which order do electrons flow through the electron transport chain?

NADH → Q → cytochrome b → cytochrome c1 → cytochrome c → cytochrome a → O2 Signup and view all the answers

What phenomenon enabled the evolution of more complex life forms approximately 2.3 billion years ago?

The appearance of molecular oxygen in the atmosphere Signup and view all the answers

What does the negative standard reduction potential indicate about a substance?

It is less favorable to donate electrons Signup and view all the answers

Why does electron flow occur spontaneously from lower E′° carriers to higher E′° carriers?

Due to inherent energy differences in electron binding Signup and view all the answers

Which option describes a characteristic of a final electron acceptor?

It must have a high reduction potential Signup and view all the answers

What is the primary mechanism by which the electron-transfer chain generates ATP?

Creating a proton-motive force Signup and view all the answers

Which of the following statements about the proton-motive force is incorrect?

It only involves electrical potential energy. Signup and view all the answers

In the equation for free-energy change (∆G), what does the variable 'Z' represent?

The absolute value of the electrical charge of the ion Signup and view all the answers

When calculating the free-energy change (∆G) using pH values, what does a positive pH difference indicate?

The intermembrane space is more acidic than the matrix. Signup and view all the answers

What is the significance of the transmembrane electrical potential (∆ψ) in the calculation of proton-motive force?

It adds to the total energy available for ATP synthesis. Signup and view all the answers

If the pH of the matrix is 0.75 units more alkaline than that of the intermembrane space, what would the pH difference indicate?

Low concentration of protons in the intermembrane space. Signup and view all the answers

Which factor does NOT contribute to the creation of the proton-motive force?

Chemical potential energy from ATP Signup and view all the answers

In the equation for calculating free-energy change, what does the term RT signify?

The ideal gas constant multiplied by temperature Signup and view all the answers

What is the role of the β subunit conformations in ATP synthase?

They facilitate the synthesis of ATP through distinct binding affinities. Signup and view all the answers

What occurs during the binding-change mechanism in ATP synthase?

The three active sites of F1 take turns binding ATP, ADP, and Pi. Signup and view all the answers

How does the γ subunit influence the β subunits in ATP synthase?

It changes the conformation of a β subunit with every 120° rotation. Signup and view all the answers

Which conformation does a β subunit adopt right after the synthesis of ATP?

β-empty conformation. Signup and view all the answers

Which of the following statements regarding the roles of the F1 and Fo components of ATP synthase is false?

Fo allows protons to flow and is involved in ATP hydrolysis. Signup and view all the answers

What is the result of proton translocation in the context of ATP synthesis?

It leads to the rotation of the γ subunit, triggering conformational changes. Signup and view all the answers

What is the significance of the β-ATP conformation in ATP synthase?

It is essential for the tight binding and retention of ATP. Signup and view all the answers

Which of the following statements is true regarding ATP synthase's operational mechanism?

Three protons must flow through Fo to synthesize one ATP molecule. Signup and view all the answers

Which statement about ATP synthase is true?

Protons flow through the Fo pore to drive the rotation of the c ring and γ subunit. Signup and view all the answers

What is the maximal P/O ratio when NADH is the electron source in a organism with dysfunctional succinate dehydrogenase?

2 Signup and view all the answers

What does the P/O ratio indicate regarding mitochondrial function?

The efficiency of ATP synthesis relative to oxygen consumption. Signup and view all the answers

How does the number of c subunits in the Fo complex affect the P/O ratio?

Different numbers of c subunits will lead to varying P/O ratios among species. Signup and view all the answers

Which component of ATP synthase undergoes transient protonation to drive rotation?

The c subunits. Signup and view all the answers

What is one consequence of the dysfunctional succinate dehydrogenase in the garden slug?

Reduced efficiency of ATP synthesis despite continued oxidative phosphorylation. Signup and view all the answers

What happens to proton flow in the ATP synthase mechanism?

Proton flow drives the rotation of the c ring and attached γ subunit. Signup and view all the answers

Which of the following P/O ratios would be consistent with electrons entering the respiratory chain at Complex I?

2.5 Signup and view all the answers

Study Notes

Oxidative Phosphorylation

Oxidative phosphorylation is a central role in eukaryotic aerobic metabolism.
ATP production isn't the only function of mitochondria.
Mitochondria host the citric acid cycle and fatty acid β-oxidation pathways.
Mitochondria are involved in amino acid oxidation, thermogenesis, steroid synthesis, and apoptosis.
Mitochondrial discovery has stimulated current research on mitochondrial biochemistry.
Mitochondria trace their evolutionary origin to bacteria.
An endosymbiotic relationship existed between bacteria and primitive eukaryotes over 1.45 billion years ago.
Mitochondria are ubiquitous in modern eukaryotes.
Their bacterial origin is evident in almost every aspect of their structure and function.
Electrons flow from electron donors to a final electron acceptor with a large reduction potential in a chain of membrane-bound carriers.
Molecular oxygen (O2) is the final acceptor.
The appearance of oxygen in the atmosphere approximately 2.3 billion years ago, and its use in living systems through oxidative phosphorylation, made complex life forms possible.
The free energy from electron flow is coupled with the transport of protons across a proton-impermeable membrane.
Fuel oxidation free energy is thus conserved as a transmembrane electrochemical potential.
Transmembrane proton flow through specific protein channels provides the free energy for ATP synthesis.
The process is catalyzed by a membrane protein complex (ATP synthase).
This complex couples proton flow to phosphorylation of ADP.
The chemiosmotic theory describes the relationship between the transmembrane difference and ATP synthesis.
The inner mitochondrial membrane is impermeable to most small molecules and ions.
Transport across this membrane requires specific transporters; porins allow small molecules to pass through the outer membrane.
The mitochondrial matrix contains the pyruvate dehydrogenase complex, citric acid cycle enzymes, fatty acid β-oxidation pathway enzymes, and amino acid oxidation pathways enzymes.
The inner mitochondrial membrane segregates cytosolic and matrix metabolic pathways intermediates and enzymes.
The order of carriers in the electron transport chain is NADH → Q → cytochrome b → cytochrome c₁ → cytochrome c → cytochrome a → cytochrome a3 → O2.
This order has been confirmed by three approaches.
Ubiquinone (Coenzyme Q) and cytochromes are electron-carrying molecules in the respiratory chain.
Flavoproteins and iron-sulfur proteins are also involved.
Cytochromes a, b, and c are distinguished by their light-absorption spectra.
Cytochrome c is loosely bound to its associated protein.
Cytochromes a and b are integral proteins of the inner mitochondrial membrane.
Iron-sulfur proteins contain iron in association with inorganic sulfur atoms.
They participate in one-electron transfers.
Complex I (NADH dehydrogenase), Complex II (succinate dehydrogenase), Complex III (ubiquinone-cytochrome c oxidoreductase), and Complex IV (cytochrome oxidase) catalyze electron transfer in separate but linked phases of respiration.
Flavoproteins and iron-sulfur proteins are important components in complex electron transfer reactions.
Ubiquinone (coenzyme Q) readily diffuses within the inner mitochondrial membrane and plays a central role in coupling electron flow to proton movement.
Cytochromes are proteins with characteristic strong absorption of visible light due to iron-containing heme prosthetic groups.
They are one-electron carriers in the electron transport chain.
The mitochondrial matrix contains enzymes of the citric acid cycle (malate dehydrogenase), the β-oxidation pathway (acyl-CoA dehydrogenase), and amino acid oxidation (glutamate dehydrogenase).
Glycolysis and fermentation enzymes (lactate dehydrogenase) are located in the cytosol.
Cristae are convolutions in the inner membrane of the mitochondrion.
Mitochondria in cells with high metabolic activity have more cristae.
During cell growth and division, mitochondria divide by fission.
Stressful conditions can trigger mitochondrial fission.
Mitophagy is the breakdown of mitochondria and amino acid, nucleotide, and lipid recycling.
Small mitochondria fuse to form long, thin, tubular organelles when stress is relieved.
The respiratory chain consists of a series of electron carriers.
Dehydrogenases collect electrons and funnel them into universal electron acceptors NAD+ or NADP+ and flavin nucleotides (FMN or FAD).
Nicotinamide nucleotide-linked dehydrogenases catalyze reversible reactions of the NAD+ or NADP+ types.
Two hydrogen atoms are removed from the reduced substrates.
One is transferred as a hydride ion (:H-) to NAD(P)+.
One is released as H+ into the medium.
Important reactions are catalyzed by NAD(P)+-linked dehydrogenases (Table 19-1).
Oxidative phosphorylation requires electron flow from electron donors to a final electron acceptor, typically molecular oxygen (O2).
The flow of electrons through Complexes I, II, III, and IV results in the pumping of protons across the inner mitochondrial membrane, creating a proton gradient across the membrane.
The electron-transport chain of the respiratory chain generates ATP by creating a proton-motive force.
The proton-motive force provides energy for ATP synthesis from ADP and Pi.
The chemiosmotic model describes the coupling of ATP synthesis to an electrochemical proton gradient.
The proton-motive force is composed of chemical and electrical potential energy, resulting from the difference in [H+] gradient.
2 NADH + 2H+ + O2 → 2NAD+ + 2H2O
The mass-action ratio (ATP)/([ADP][Pi]) is a measure of a cell's energy status.
A rise in ADP concentration leads to an increased rate of respiration.
Inhibitory proteins such as IF1 can prevent ATP hydrolysis during hypoxic conditions.
Chemical uncouplers such as DNP and FCCP dissipate the proton gradient.
In the absence of an oxidizable substrate, the proton-motive force alone drives ATP synthesis.
Species differences exist in the number of c subunits in the F₀ complex, and this impacts the P/O ratio.
Mitochondrial ATP synthase F₁ has an α3β3γδ subunits composition. Each ẞ subunit can assume three different conformations: β-ATP (tight binding), β-ADP (loose binding), and β-empty (very loose binding).
The Fo complex has ab2cn composition (n from 8–17). c ring is an arrangement of c subunits into two concentric circles.
Proton translocation causes a rotation of F₀ and Y, causing conformational changes within αβ pairs, and promotes ADP + Pi condensation to ATP.
The y subunit rotates in one direction when FoF₁ synthesizes ATP, and in the opposite direction when hydrolyzing ATP.
The glycerol 3-phosphate shuttle is necessary for oxidative phosphorylation in the brain.
The malate-aspartate shuttle is necessary for oxidative phosphorylation in liver.
Mitochondrial genomes are less efficient at repairing DNA damage in comparison to the nuclear genome and are primarily inherited from the female lineage.
Mutations in mitochondrial DNA accumulate over an organism's lifetime and frequently cause disease with heteroplasmic cells having varying degrees of severity.
The energy of electron transfer is efficiently conserved in a proton gradient. The change in standard reduction potential is 1.14 V.
The standard free-energy change is -220 kJ/mol of NADH.
Mitochondrial P-450 monooxygenases catalyze steroid hydroxylations, which occur in steroidogenic tissues.
The cytochrome P-450 family catalyzes a series of hydroxylation reactions to synthesize steroid hormones.
A flavoprotein and an iron-sulfur protein carry electrons from NADPH to the P-450 heme. All P-450 enzymes have a heme that interacts with O2, and a substrate binding site for specificity.
The inner mitochondrial membrane is impermeable to NADH and NAD+. Cytosolic NADH must be transported into mitochondria.
Specific shuttle systems carry reducing equivalents from cytosolic NADH into mitochondria.
Mitochondrial DNA defects frequently occur due to reactive oxygen species (ROS) exposure, and mtDNA replication system having lower correction effectiveness compared to the nuclear system.
Animals inherit their mitochondria essentially solely from the female parent.
The chemiosmotic mechanism likely evolved before the emergence of eukaryotes.
Mitochondrial donation implies transplantation of an ovum's nuclear genes into an enucleated ovum. This procedure creates an ovum free of mutations that leads to a mitochondrial disease and raises ethical issues.

Thermogenesis

Brown adipose tissue (BAT) is an adipose tissue in newborn mammals.
It generates heat through fuel oxidation.
Uncoupling protein 1 (UCP1) is a long-chain fatty acid/H+ symporter in BAT.
It provides a path for protons to return to the matrix without passing through the FoF₁ complex.
This action results in dissipation of oxidation energy as heat.
Hydrolysis of phosphocreatine also releases heat in thermogenesis.
Hibernating animals depend on uncoupled BAT mitochondria activity to generate heat during their long dormancy periods.

Steroid Synthesis

Mitochondria are the site of steroid hormone production.
Steroidogenic tissues (adrenal gland, gonads, liver, kidney) contain these reactions.
Mitochondria contain cytochrome P-450 enzymes involved in steroid synthesis.
The reactions catalyze a series of hydroxylations to synthesize steroid hormones from a sterol.
These enzymes possess a critical heme group.

Apoptosis

Apoptosis (programmed cell death) is a cellular process where individual cells die for the organism's benefit.
It can be triggered during normal embryonic development, by external signals, or from internal events (DNA damage, viral infection, oxidative stress, etc.).
Mitochondria are central to apoptosis initiation.
Permeability transition pore complex (PTPC) is a multisubunit membrane protein that increases membrane permeability.
Apaf-1 (apoptosis protease activating factor-1) monomers interact with cytochrome c from mitochondria, resulting in the formation of an apoptosome.
Caspases are proteases that are crucial during the apoptosis process.

Mitochondrial Genes

Thirteen mitochondrial proteins are encoded by the mitochondrial genome and synthesized within mitochondria.
Approximately 1,200 mitochondrial proteins are encoded by nuclear genes and imported into mitochondria.
Mitochondrial genes are often associated with a high level of specific disease outcomes depending on the specific mutations and the organism.
The human mitochondrial genome is circular rather than linear and is less efficient in repair compared to nuclear DNA.
The mitochondrial genome is predominantly inherited from the maternal lineage.
Mitochondrial encephalomyopathies represent a group of disorders that mainly affect the brain and skeletal muscle.
Leber hereditary optic neuropathy (LHON) is a rare ailment associated with mutations within the mitochondrial Complex 1 (e.g. a single amino acid substitution.)
Myoclonic epilepsy with ragged-red fibers (MERRF) syndrome results from a mutation within a tRNA gene.

Oxidative Phosphorylation Regulation

Acceptor control of respiration is regulated by ADP, which is the major P₁ acceptor.
The rate of O2 consumption increases with the availability of ADP.
The acceptor control ratio is the maximal rate of ADP-induced O2 consumption divided by the basal rate in the absence of ADP; this ratio is at least 10 for some animal tissues.
The mass-action ratio([ATP]/([ADP][P;])) is a crucial factor in regulating oxidative phosphorylation rates. Higher ADP levels correlate with more active oxidative phosphorylation, when ADP is depleted, so does the rate of oxidative phosphorylation.
Oxidative phosphorylation is coordinated with the rates of electron transfer, the citric acid cycle, pyruvate oxidation, and glycolysis as cellular energy needs change.

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Description

Explore the intricacies of the electron transport chain in this quiz, focusing on Complex II, reactive oxygen species, and metabolic pathways. Understand the importance of oxygen, mitochondrial functions, and key enzymes involved in energy production. Test your knowledge on the role of coenzyme A and the chemiosmotic theory in cellular respiration.