True or False [ ] Chemiosmotic theory provides the intellectual framework for un
ID: 705782 • Letter: T
Question
True or False
[ ] Chemiosmotic theory provides the intellectual framework for understanding many biological energy transductions, including oxidative phosphorylation and photophosphorylation. The mechanism of energy coupling is similar in both cases: the energy of electron flow is conserved by the concomitant pumping of protons across the membrane, producing an electrochemical gradient, the proton-motive force.
[ ] In mitochondria, hydride ions removed from substrates (such as ?-ketoglutarate and malate) by NAD-linked dehydrogenases donate electrons to the respiratory (electron-transfer) chain, which transfers the electrons to molecular H2O, reducing it to O2.
[ ] Reducing equivalents from NADH are passed through a series of Fe-S centers to ubiquinone, which transfers the electrons to cytochrome b, the first carrier in Complex III. In this complex, electrons take two separate paths through two btype cytochromes and cytochrome c1 to an Fe-S center. The Fe-S center passes electrons, one at a time, through cytochrome c and into Complex IV, cytochrome oxidase. This copper-containing enzyme, which also contains cytochromes ? and ?3,accumulates electrons, then passes them to O2, reducing it to H2O.
[ ] Some electrons enter this chain of carriers through alternative paths. Succinate is oxidized by succinate dehydrogenase (Complex II), which contains a flavoprotein that passes electrons through several Fe-S centers to ubiquinone. Electrons derived from the oxidation of fatty acids pass to ubiquinone via the electron-transferring flavoprotein.
[ ] Potentially harmful reactive oxygen species produced in mitochondria are activated by a set of protective enzymes, including superoxide dismutase and glutathione peroxidase.
[ ] The flow of electrons through Complexes I, III, and IV results in pumping of protons across the inner mitochondrial membrane, making the matrix alkaline relative to the intermembrane space. This proton gradient provides the energy (in the form of the proton-motive force) for ATP synthesis from ADP and Pi by ATP synthase (FoF1 complex) in the inner membrane.
[ ] ATP synthase carries out “rotational catalysis,” in which the flow of protons through F1 causes each of three nucleotide-binding sites in Fo to cycle from (ADP + Pi)-bound to ATP-bound to empty conformations.
[ ] ATP formation on the enzyme requires little energy; the role of the proton-motive force is to push ATP from its binding site on the synthase.
[ ] The ratio of ATP synthesized per ½ O2 reduced to H2O (the P/O ratio) is about 1.5 when electrons enter the respiratory chain at Complex I, and 2.5 when electrons enter at ubiquinone. This ratio may vary somewhat in different organisms based on the number of c subunits in the Fo complex.
[ ] The inner mitochondrial membrane is impermeable to NADH and NAD+ , but NADH equivalents are moved from the cytosol to the matrix by either of two shuttles. NADH equivalents moved in by the malate-aspartate shuttle enter the respiratory chain at Complex I and yield a P/O ratio of 1.5; those moved in by the glycerol 3-phosphate shuttle enter at ubiquinone and give a P/O ratio of 2.5.
[ ] Oxidative phosphorylation is regulated by cellular energy demands. The intracellular [ADP] and the mass-action ratio [ATP]/([ADP][Pi]) are measures of a cell’s energy status.
[ ] ATP and ADP concentrations set the rate of electron transfer through the respiratory chain via a series of interlocking controls on respiration, glycolysis, and the citric acid cycle.
Explanation / Answer
True or False
[True ] Chemiosmotic theory provides the intellectual framework for understanding many biological energy transductions, including oxidative phosphorylation and photophosphorylation. The mechanism of energy coupling is similar in both cases: the energy of electron flow is conserved by the concomitant pumping of protons across the membrane, producing an electrochemical gradient, the proton-motive force.
Explanation: chemiosmotic coupling deals with linkage of electron transport, proton pumping and ATP synthesis
[ False] In mitochondria, hydride ions removed from substrates (such as ?-ketoglutarate and malate) by NAD-linked dehydrogenases donate electrons to the respiratory (electron-transfer) chain, which transfers the electrons to molecular H2O, reducing it to O2.
Explanation: The electrons reduces the 2 hydrogen ion (2 H+) in the presence of half mole of Oxygen to form 1 mole of water molecule
[ True] Reducing equivalents from NADH are passed through a series of Fe-S centers to ubiquinone, which transfers the electrons to cytochrome b, the first carrier in Complex III. In this complex, electrons take two separate paths through two b type cytochromes and cytochrome c1 to an Fe-S center. The Fe-S center passes electrons, one at a time, through cytochrome c and into Complex IV, cytochrome oxidase. This copper-containing enzyme, which also contains cytochromes ? and ?3,accumulates electrons, then passes them to O2, reducing it to H2O.
Explanation: Oxygen is reduced to water
[True ] Some electrons enter this chain of carriers through alternative paths. Succinate is oxidized by succinate dehydrogenase (Complex II), which contains a flavoprotein that passes electrons through several Fe-S centers to ubiquinone. Electrons derived from the oxidation of fatty acids pass to ubiquinone via the electron-transferring flavoprotein.
Explanation: Complex II involves transfer of electrons from Succinate to ubiquinone
[False ] Potentially harmful reactive oxygen species produced in mitochondria are activated by a set of protective enzymes, including superoxide dismutase and glutathione peroxidase.
Explanation: Glutathione peroxidase, superoxide dismutase and catalase are the most important enzymes of the cell antioxidant defense system. SOD precipitates the harmful reactive oxygen there by helps the mitochondrial cell.
[True ] The flow of electrons through Complexes I, III, and IV results in pumping of protons across the inner mitochondrial membrane, making the matrix alkaline relative to the intermembrane space. This proton gradient provides the energy (in the form of the proton-motive force) for ATP synthesis from ADP and Pi by ATP synthase (FoF1 complex) in the inner membrane.
Explanation: ATP synthesis from ADP and Pi by ATP synthase (FoF1 complex) in the inner membrane
[True ] ATP synthase carries out “rotational catalysis,” in which the flow of protons through F1 causes each of three nucleotide-binding sites in Fo to cycle from (ADP + Pi)-bound to ATP-bound to empty conformations.
Explanation: The rotation of the ? subunit conformers during rotational catalysis.
[ False] ATP formation on the enzyme requires little energy; the role of the proton-motive force is to push ATP from its binding site on the synthase.
Explanation: Proton motive force is used to couple ADP + P i to form ATP
[ True] The ratio of ATP synthesized per ½ O2 reduced to H2O (the P/O ratio) is about 1.5 when electrons enter the respiratory chain at Complex I, and 2.5 when electrons enter at ubiquinone. This ratio may vary somewhat in different organisms based on the number of c subunits in the Fo complex.
Explanation: NADH generates 2.5 ATP and FADH2 generates 1.5 ATP
[True ] The inner mitochondrial membrane is impermeable to NADH and NAD+ , but NADH equivalents are moved from the cytosol to the matrix by either of two shuttles. NADH equivalents moved in by the malate-aspartate shuttle enter the respiratory chain at Complex I and yield a P/O ratio of 1.5; those moved in by the glycerol 3-phosphate shuttle enter at ubiquinone and give a P/O ratio of 2.5.
Explanation: NADH generates 2.5 ATP and FADH2 generates 1.5 ATP
[ True] Oxidative phosphorylation is regulated by cellular energy demands. The intracellular [ADP] and the mass-action ratio [ATP]/([ADP][Pi]) are measures of a cell’s energy status.
Explanation: rate of respiration (O2 consumption) in mitochondria is under tight regulation; generally limited by the availability of ADP as a substrate for phosphorylation.
[True ] ATP and ADP concentrations set the rate of electron transfer through the respiratory chain via a series of interlocking controls on respiration, glycolysis, and the citric acid cycle.
Explanation: dependence of the rate of O2 consumption on the concentration of the Pi acceptor ADP, called acceptor control of respiration.
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