This process is called chemiosmosis. The electron transport chain is a series of proteins located on the inner membrane of the mitochondria. The first enzyme in the electron transport chain is the NADH-CoQ oxidoreductase, also known as NADH dehydrogenase or complex I, which is the first entry of protons through the electron transport chain. As two electrons pass through complex I, four protons are pumped from the mitochondrial matrix into the intermembrane space.
The second enzyme that allows protons to passes through the electron transport chain is succinic-coenzyme Q oxidoreductase, also known as succinate dehydrogenase or complex II. It catalyzes the oxidation of succinic acid to form fumarate and the reduction of coenzyme Q10 to ubiquinone QH2.
This reaction does not involve the transfer of electrons, nor does it pump out protons, providing less energy to compare with the oxidation process of NADH. The third entry to the proton on the electron transport chain is electron transfer flavin-coenzyme Q oxidoreductase, also known as electron transfer flavin dehydrogenase, which reduces Q10 by using electrons from electron transfer flavin in the mitochondrial matrix.
Coenzyme Q-cytochrome C reductase, also known as complex III, catalyzes the oxidation of QH2, and the reduction of cytochrome c and ferritin. In this reaction, cytochrome C carries an electron. Coenzyme Q is reduced to QH2 on one side of the mitochondrial membrane, while QH2 is oxidized to coenzyme Q10 on the other side, resulting in the transfer of protons on the membrane, which also contributes to the formation of proton gradients.
The last protein complex in the electron transport chain is cytochrome c oxidase, also called complex IV. It mediates the final reaction on the electron transport chain - transferring electrons to the final electron receptor oxygen - oxygen reduces to water - pumping protons through the membrane. At the end of this reaction, protons that directly pumped out and that consumed by the reduction of oxygen to water increase the proton gradient. There is another electron-donating molecule - FADH2 in eukaryotes.
FADH2 is also the intermediate metabolite during the earlier stage of cellular respiration such as glycolysis or citric acid cycle. And this reaction does not pump out protons either. The subsequent reactions are nearly the same as those in the NADH2 electron transport chain. Prokaryotes such as bacteria and archaea have many electron transfer enzymes that can use a very wide range of chemicals as substrates.
As the same with eukaryotes, electron transport in prokaryotic cells also uses the energy released by oxidation from the substrate to pump protons across the membrane to create an electrochemical gradient, which drives ATP synthase to generate ATP. The difference is that bacteria and archaea use many different substrates as electron donors or electron receptors.
This also helps prokaryotes to survive and grow in different environments. Under normal conditions, electron transfer and phosphorylation are tightly coupled. Some compounds can affect electron transport or interfere with phosphorylation reactions, all of which cause oxidative phosphorylation abnormalities.
Here introduce four factors affecting oxidative phosphorylation. Respiratory chain inhibitor: A substance that blocks electron transport at a certain part of the respiratory chain and inhibits the oxidation process. In prokaryotes, the conversion of phosphoenolpyruvate PEP to pyruvate provides the energy to transport glucose across the cytoplasmic membrane and, in the process, adds a phosphate group to glucose producing glucose 6-phosphate.
The 6-carbon fructose 1,6 biphosphate is split to form two, 3-carbon molecules: glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. Two molecules of glyceraldehyde 3-phosphate will now go through each of the remaining steps in glycolysis producing two molecules of each product. Through an intermediate step called the transition reaction, the two molecules of pyruvate then enter the citric acid cycle to be further broken down and generate more ATPs by oxidative phosphorylation.
Learning Objectives Briefly describethe function of glycolysis during aerobic respiration and indicate the reactants and products. State whether or not glycolysis requires oxygen. Compare where glycolysis occurs in prokaryotic cells and in eukaryotic cells. State whether steps 1 and 3 of glycolysis are exergonic or endergonic and indicate why. State why one molecule of glucose is able to produce two molecules of pyruvate during glycolysis. Define substrate-level phosphorylation.
State the total number and the net number of ATP produced by substrate-level phosphorylation during glycolysis. During aerobic respiration, state what happens to the 2 NADH produced during glycolysis. During aerobic respiration, state what happens to the two molecules of pyruvate produced during glycolysis. Study the material in this section and then write out the answers to these question.
Do not just click on the answers and write them out. This will not test your understanding of this tutorial. Learning Objectives Define photophosphorylation. Describe substrate-level phosphorylation and name to energy-generating pathways in which this occurs. Define oxidative phosphorylation. Name the two components of a hydrogen atom. Describe an oxidation-reduction reaction. Define dehydrogenation and hydrogenation.
Describe an electron transport chain and state its cellular function. Briefly describethe chemiosmotic theory of generation of ATP as a result of an electron transport chain. State the function of ATP synthases. YouTube movie illustrating the light reactions during photosynthesis including photophosphorylation. Oxidative Phosphorylation Oxidative phosphorylation is the production of ATP using energy derived from the transfer of electrons in an electron transport system and occurs by chemiosmosis.
FAD , or flavin adenine dinucleotide, is a coenzyme that also works in conjunction with an enzyme called a dehydrogenase.
NADPH is not used for ATP synthesis but its electrons provide the energy for certain biosynthesis reactions such as ones involved in photosynthesis. Flash animation illustrating energy release during oxidation-reduction reactions. Flash animation illustrating the development of proton motive force as a result of chemiosmosis and ATP production by ATP synthase. Flash animation illustrating ATP production by chemiosmosis during aerobic respiration in a prokaryotic bacterium.
Summary Photophosphorylation uses the radiant energy of the sun to drive the synthesis of ATP. Substrate-level phosphorylation is the production of ATP from ADP by a direct transfer of a high-energy phosphate group from a phosphorylated intermediate metabolic compound in an exergonic catabolic pathway.
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