Carbohydrate Metabolism - Biochemistry

In the citric acid cycle, succinate dehydrogenase converts succinate to fumarate with the production also of a molecule of (flavin adenine dinucleotide) that supplies electrons to the electron transport chain. Mitochondrial glycerol-3-phosphate dehydrogenase-2 is an enzyme of the glycerol-3-phosphate shuttle that produces and converts glycerol-3-phosphate into dihydroxyacetone phosphate. The other enzymes are part of the citric acid cycle, but do not produce (aconitase converts citrate to isocitrate, while succinyl-CoA synthetase converts succinyl-CoA to succinate).

The correct answer is cyanide. This compound acts to inhibit cytochrome C oxidase, otherwise known as Complex IV of the electron transport chain. By inhibiting this complex, cyanide effectively halts the flow of electrons through the chain. Consequently, protons are not able to be pumped from the matrix to the intermembrane space and thus, a proton gradient cannot be established. Without a proton gradient, protons will not flow through ATP synthase, hence no ATP will be produced.

Oligomycin, on the other hand, acts to inhibit ATP synthase, which means that ATP will not be able to be produced. However, electrons are still able to flow through the chain, which means that protons are still able to be pumped across the inner membrane.

Dinitrophenol is a relatively nonpolar compound that is able to situate itself into the inner mitochondrial membrane. In doing so, it is able to dissipate the proton gradient by allowing protons to essentially be transported from the intermembrane space to the matrix without traversing through ATP synthase. Even though protons can still flow through ATP synthase to generate ATP in this scenario, the proton gradient won't be nearly as potent because they now have an alternative route to the matrix.

Methotrexate acts to competitively inhibit the enzyme known as dihydrofolate reductase. This enzyme has nothing to do with the electron transport chain, and thus will have no effect on ATP synthesis. Commonly, this drug is used as an anti-cancer agent because its substrate, dihydrofolate, is a compound that is used in the syntheis of thymine nucleotides for DNA synthesis. Inhibiting dihydrofolate reductase effectively reduces the production of thymine, which can negatively impact DNA replication in rapidly dividing cancer cells.

Likewise, allopurinol has nothing to do with the electron transport chain. This drug acts as an inhibitor of the enzyme xanthine oxidase, which is responsible for synthesizing uric acid. High levels of uric acid can lead to the development of gout, and thus, this drug is typically used to help treat people suffering from gout.

Potassium cyanide inhibits cellular respiration by acting on mitochondrial cytochrome c reductase (leading to hypoxia and death). Rotenone also affects oxidative phosphorylation, by inhibiting electron transfer from cytochrome 1 to ubiquinone, making it a potent insecticide. Oligomycin inhibits ATP synthase, also slowing flow of the electron transport chain. Fructose 2,6-biphosphate affects the activity of enzymes regulating glycolysis and gluconeogenesis. Dinitrophenol dissipates the proton gradient across mitochondrial membranes, and shuttles protons across them, inhibiting ATP production.

Aerobic respiration is a process that utilizes the electron transport chain in order to oxidize glucose into energy. If a chemical were added that inhibited the electron transport chain, the cell would no longer be able to fully oxidize glucose. Therefore, oxygen consumption will decrease. Furthermore, since the cell is now in a situation in which it is not able to make as much energy per glucose molecule as before, it will need to increase its consumption of glucose in order to generate enough energy through anaerobic respiration alone.

Oligomycin is an antibiotic that inhibits ATP synthase. It works by binding to the stalk of ATP synthase. This prevents proton re-entry into the mitochondrial matrix. This results in a halt of the proton motive force that ATP synthase uses to created ATP from one unit of ADP and one unit of inorganic phosphate. Rotenone is a pesticide and fish poison that inhibits NADH dehydrogenase in complex I causing the levels of NADH to increase. This results in a halt of the electron transport chain. Antimycin is a fungal antibiotic that inhibits complex III of the electron transport chain. Antimycin prevents the transfer of electrons through the cytochrome b-c complex. Cyanide is a gas that inhibits complex IV of the electron transport chain. Cyanide combines with cytochrome oxidase and prevents the transfer of electrons to oxygen.

Antimycin is a fungal antibiotic that inhibits complex III of the electron transport chain. Antimycin prevents the transfer of electrons through the cytochrome b-c complex. Oligomycin is an antibiotic that inhibits ATP synthase. It works by binding to the stalk of ATP synthase. This prevents proton re-entry into the inner mitochondrial matrix. This results in a halt of the proton motive force that ATP synthase uses to created ATP from one unit of ADP and one unit of inorganic phosphate. Rotenone is a pesticide and fish poison that inhibits NADH dehydrogenase in complex I causing the levels of NADH to increase. This results in a halt of the electron transport chain. Cyanide is a gas that inhibits complex IV of the electron transport chain. Cyanide combines with cytochrome oxidase and prevents the transfer of electrons to oxygen.

Rotenone is a pesticide and fish poison that inhibits NADH dehydrogenase in complex I causing the levels of NADH to increase. This results in a halt of the electron transport chain. Oligomycin is an antibiotic that inhibits ATP synthase. It works by binding to the stalk of ATP synthase. This prevents proton re-entry into the mitochondrial matrix. This results in a halt of the proton motive force that ATP synthase uses to created ATP from one unit of ADP and one unit of inorganic phosphate. Antimycin is a fungal antibiotic that inhibits complex III of the electron transport chain. Antimycin prevents the transfer of electrons through the cytochrome b-c complex. Cyanide is a gas that inhibits complex IV of the electron transport chain. Cyanide combines with cytochrome oxidase and prevents the transfer of electrons to oxygen.

Cyanide is a gas that inhibits complex IV of the electron transport chain. Cyanide combines with cytochrome oxidase and prevents the transfer of electrons to oxygen. Antimycin is a fungal antibiotic that inhibits complex III of the electron transport chain. Antimycin prevents the transfer of electrons through the cytochrome b-c complex. Oligomycin is an antibiotic that inhibits ATP synthase. It works by binding to the stalk of ATP synthase. This prevents proton re-entry into the mitochondrial matrix. This results in a halt of the proton motive force that ATP synthase uses to created ATP from one unit of ADP and one unit of inorganic phosphate. Rotenone is a pesticide and fish poison that inhibits NADH dehydrogenase in complex I causing the levels of NADH to increase. This results in a halt of the electron transport chain.

CoQ10 is produced in the liver and oxidizes enzyme complex II. It is subsequently oxidized by enzyme complex III in the ETC. Oxygen is the final acceptor of electrons in the ETC.

Without a terminal electron acceptor, the electrons of and would have nowhere to be released, all of the complexes would be "backed up" as each complex would not be able to pass off its electrons to the next complex. ATP production would come to a standstill.

Without oxygen to receive the electrons, the entire flow of the electron transportation chain halts, as well as ATP production. It is the continuous flow of electrons through the ETC complexes that allows a mitochondria to harness the energy of the electrons that and donate. This energy is used to pump protons across the intermembrane space of a mitochondria. The re-entry of these protons through ATP synthase is what drives the production of ATP.

In short, no electron flow means no proton pumps and no re-entry of those protons through ATP synthase. A cell could potentially resort to glycolysis to produce ATP, and can regenerate or using anaerobic fermentation such as alcohol fermentation of lactic acid fermentation.

The electron transport chain passes electrons thru its main components: complex I (NADH dehydrogenase), coenzyme Q, complex III, cytochrome C, and complex IV. Complex IV is the cytochrome oxidase complex and it is inhibited by cyanide, carbon monoxide and azide. Cyanide binds irreversibly to complex IV preventing electron transfer.

Uncouplers of the electron transport chain decrease the proton gradient and thus decrease ATP synthesis. Most energy from the electron transport chain is released as heat. The most common uncouplers are 2,4-dinitrophenol and aspirin, as well as thermogenin. Carbon monoxide is an inhibitor of the electron transport chain, not an uncoupler. Nitric oxide does not affect directly the electron transport chain.

The electron transport system is the only metabolic process listed that directly requires molecular oxygen. Oxygen is the final electron acceptor (it is one of the most electronegative atoms in our bodies) in the electron transport chain. This is the same as saying that oxygen has the highest reduction potential, and is capable of receiving electons. If oxygen is not present to accept the electron from the final enzyme complex in the inner mitochondrial membrane, then electron transport will be inhibited and thus no ATP will be produced via chemiosmosis.

Note that the Krebs cycle, citric acid cycle, and tricarboxylic acid cycle (TCA cycle) all refer to the same process, and do not directly require oxygen (oxygen is neither a reactant nor a product in any of the steps). However, oxygen is indirectly required, as there is no point to this cycle without subsequent oxidative phosphorylation. Thus in the absence of oxygen, of the choices shown, only glycolysis will proceed uninhibited.

The electron transport chain generates the most ATP out of all three major phases of cellular respiration. Glycolysis produces a net of 2 ATP per molecule of glucose. In the Krebs cycle, there is one GTP (which is an ATP equivalent) generate in the conversion of succinyl-CoA to succinate. However, the majority of the ATP produced during cellular respiration occurs at the electron transport chain by the reduction of coenzymes NADH and . This subsequently results in the generation of the proton motive force which ATP synthase uses to generate ATP from one unit of ADP and one unit of inorganic phosphate.

In a eukaryote, oxidative phosphorylation occurs in the mitochondria because this is where the cell is able to set up a proton gradient. However, prokaryotes do not have mitochondria - they have no membrane-bound organelles at all. Therefore, the proton gradient that drives ATP synthesis in oxidative phosphorylation is created across the cell membrane.

With the excess buildup of protons in the matrix, the only thing that will be inhibited is the generation of ATP by ATP synthase. The other processes in cellular respiration focus more on creation of high energy electron carriers, and therefore will continue as normal.

Predictably, a gain in oxygen is known as oxidation, while a loss of oxygen is reduction. Hydrogen follows the opposite pattern as oxidation: removing hydrogen is oxidation, while gaining hydrogen is reduction. Therefore, the correct answer is that removing hydrogens is considered oxidation.

In order to differentiate between oxidation and reduction in terms of electron transfer, it is helpful to remember the phrase "LEO the tiger says GER". A loss of electrons is oxidation, while a gain of electrons is reduction.

During oxidative phosphorylation, is created from the previously created and . All of the other choices describe other parts of cellular respiration. In glycolysis, glucose is oxidized to pyruvate. In both glycolysis and the Krebs cycle, substrate level phosphorylation occurs. Likewise, and are produced during glycolysis and the Krebs cycle, but not during oxidative phosphorylation, where these high energy electrons are passed down a series of membrane-bound enzymes to oxygen meanwhile protons are pumped into the intermembrane space of the mitochondria.

Glycolysis occurs in the cytoplasm. Pyruvate dehydrogenase complex occurs in the mitochondrial matrix. Krebs cycle occurs in the mitochondrial matrix. Electron transport chain protein complexes are embedded in the mitochondrial inner membrane.

To answer this question, it's important to have familiarity with the process of aerobic respiration.

In the first major pathway, glycolysis is split into two molecules of pyruvate through a series of reactions. Along the way, high-energy electron carriers are produced, along with ATP.

In the next major step, pyruvate is transferred into mitochondria, where it is decarboxylated into acetyl-CoA, with a concomitant production of NADH and carbon dioxide. Hence, this is a step that produces carbon dioxide. However, it is not found in the answer choices.

The third major component of aerobic respiration is the citric acid cycle. Here, the acetyl-CoA from the previous step is completely ripped apart to provide a great deal of energy. This huge amount of energy that is liberated is because the two carbon atoms that make up the acetyl group of acetyl-CoA become completely oxidized into two molecules of carbon dioxide. In terms of the energy liberated from the cycle, ATP along with a good deal of high-energy electron carriers are produced. This component of aerobic respiration is indeed a source of carbon dioxide.

Fermentation is an anaerobic pathway and is thus not the correct answer. Depending on the organism, carbon dioxide may or may not be produced.

Finally, aerobic respiration culminates in oxidative phosphorylation. Here, all of the high energy carriers from the previous steps are fed into the electron transport chain, resulting in the production of a great amount of ATP, the main energy currency of cells. In this final major step, it is oxygen gas that is produced, not carbon dioxide.