Again Based on the Concept Map Which of the Following Processes Directly Produce the Most Atp

Chapter 4: Introduction to How Cells Obtain Energy

4.iii Citric Acid Cycle and Oxidative Phosphorylation

Learning Objectives

By the stop of this section, you volition be able to:

• Describe the location of the citric acrid cycle and oxidative phosphorylation in the prison cell
• Describe the overall upshot of the citric acid wheel and oxidative phosphorylation in terms of the products of each
• Draw the relationships of glycolysis, the citric acid cycle, and oxidative phosphorylation in terms of their inputs and outputs.

The Citric Acrid Cycle

In eukaryotic cells, the pyruvate molecules produced at the stop of glycolysis are transported into mitochondria, which are sites of cellular respiration. If oxygen is bachelor, aerobic respiration will go forward. In mitochondria, pyruvate will be transformed into a two-carbon acetyl group (by removing a molecule of carbon dioxide) that will be picked up past a carrier compound called coenzyme A (CoA), which is made from vitamin B_v. The resulting compound is called acetyl CoA. (Effigy 4.17). Acetyl CoA can be used in a variety of ways by the prison cell, only its major function is to evangelize the acetyl group derived from pyruvate to the next pathway in glucose catabolism.

Figure 4.17 Pyruvate is converted into acetyl-CoA before entering the citric acid cycle.

Similar the conversion of pyruvate to acetyl CoA, the citric acid cycle in eukaryotic cells takes place in the matrix of the mitochondria. Unlike glycolysis, the citric acid cycle is a closed loop: The final part of the pathway regenerates the compound used in the first step. The eight steps of the bike are a series of chemic reactions that produces two carbon dioxide molecules, ane ATP molecule (or an equivalent), and reduced forms (NADH and FADH₂) of NAD⁺ and FAD⁺, important coenzymes in the cell. Part of this is considered an aerobic pathway (oxygen-requiring) because the NADH and FADH₂ produced must transfer their electrons to the side by side pathway in the system, which volition utilise oxygen. If oxygen is not present, this transfer does not occur.

2 carbon atoms come into the citric acrid cycle from each acetyl group. Two carbon dioxide molecules are released on each turn of the cycle; however, these exercise non contain the same carbon atoms contributed by the acetyl grouping on that plow of the pathway. The ii acetyl-carbon atoms will eventually be released on later turns of the wheel; in this manner, all six carbon atoms from the original glucose molecule will be eventually released every bit carbon dioxide. It takes ii turns of the cycle to procedure the equivalent of one glucose molecule. Each turn of the wheel forms three loftier-energy NADH molecules and one high-energy FADH_ii molecule. These high-energy carriers volition connect with the last portion of aerobic respiration to produce ATP molecules. One ATP (or an equivalent) is also fabricated in each bike. Several of the intermediate compounds in the citric acid cycle can be used in synthesizing non-essential amino acids; therefore, the bike is both anabolic and catabolic.

Figure 4.xviii In eukaryotes, oxidative phosphorylation takes place in mitochondria. In prokaryotes, this process takes place in the plasma membrane. (Credit: modification of work by Mariana Ruiz Villareal)

Oxidative Phosphorylation

You take just read nearly two pathways in glucose catabolism—glycolysis and the citric acrid bike—that generate ATP. Most of the ATP generated during the aerobic catabolism of glucose, yet, is not generated direct from these pathways. Rather, it derives from a process that begins with passing electrons through a series of chemic reactions to a final electron acceptor, oxygen. These reactions accept identify in specialized protein complexes located in the inner membrane of the mitochondria of eukaryotic organisms and on the inner part of the cell membrane of prokaryotic organisms. The energy of the electrons is harvested and used to generate a electrochemical slope beyond the inner mitochondrial membrane. The potential energy of this gradient is used to generate ATP. The entirety of this process is called oxidative phosphorylation.

The electron transport chain (Figure 4.19a) is the last component of aerobic respiration and is the merely part of metabolism that uses atmospheric oxygen. Oxygen continuously diffuses into plants for this purpose. In animals, oxygen enters the trunk through the respiratory organization. Electron transport is a series of chemic reactions that resembles a bucket brigade in that electrons are passed rapidly from one component to the adjacent, to the endpoint of the concatenation where oxygen is the final electron acceptor and water is produced. At that place are four complexes composed of proteins, labeled I through Iv in Figure 4.xixc, and the aggregation of these four complexes, together with associated mobile, accessory electron carriers, is called the electron ship chain. The electron ship chain is present in multiple copies in the inner mitochondrial membrane of eukaryotes and in the plasma membrane of prokaryotes. In each transfer of an electron through the electron send chain, the electron loses free energy, only with some transfers, the energy is stored every bit potential free energy past using it to pump hydrogen ions beyond the inner mitochondrial membrane into the intermembrane space, creating an electrochemical gradient.

Figure 4.19 (a) The electron transport concatenation is a fix of molecules that supports a series of oxidation-reduction reactions. (b) ATP synthase is a complex, molecular motorcar that uses an H+ slope to regenerate ATP from ADP. (c) Chemiosmosis relies on the potential energy provided by the H+ gradient across the membrane.

Cyanide inhibits cytochrome c oxidase, a component of the electron transport chain. If cyanide poisoning occurs, would you expect the pH of the intermembrane space to increase or subtract? What affect would cyanide take on ATP synthesis?

Electrons from NADH and FADH₂ are passed to protein complexes in the electron send chain. Every bit they are passed from one complex to another (there are a total of four), the electrons lose free energy, and some of that energy is used to pump hydrogen ions from the mitochondrial matrix into the intermembrane space. In the fourth protein complex, the electrons are accustomed by oxygen, the terminal acceptor. The oxygen with its extra electrons then combines with two hydrogen ions, farther enhancing the electrochemical slope, to form water. If there were no oxygen nowadays in the mitochondrion, the electrons could not be removed from the system, and the unabridged electron transport chain would dorsum up and stop. The mitochondria would be unable to generate new ATP in this way, and the cell would ultimately dice from lack of free energy. This is the reason we must exhale to draw in new oxygen.

In the electron transport chain, the free free energy from the series of reactions just described is used to pump hydrogen ions across the membrane. The uneven distribution of H⁺ ions across the membrane establishes an electrochemical gradient, owing to the H⁺ ions' positive accuse and their college concentration on one side of the membrane.

Hydrogen ions diffuse through the inner membrane through an integral membrane protein called ATP synthase (Figure 4.19b). This complex protein acts every bit a tiny generator, turned by the force of the hydrogen ions diffusing through information technology, down their electrochemical gradient from the intermembrane space, where there are many mutually repelling hydrogen ions to the matrix, where in that location are few. The turning of the parts of this molecular machine regenerate ATP from ADP. This flow of hydrogen ions across the membrane through ATP synthase is called chemiosmosis.

Chemiosmosis (Effigy four.19c) is used to generate 90 per centum of the ATP made during aerobic glucose catabolism. The effect of the reactions is the production of ATP from the energy of the electrons removed from hydrogen atoms. These atoms were originally role of a glucose molecule. At the end of the electron send system, the electrons are used to reduce an oxygen molecule to oxygen ions. The extra electrons on the oxygen ions concenter hydrogen ions (protons) from the surrounding medium, and water is formed. The electron transport chain and the production of ATP through chemiosmosis are collectively called oxidative phosphorylation.

ATP Yield

The number of ATP molecules generated from the catabolism of glucose varies. For example, the number of hydrogen ions that the electron transport chain complexes can pump through the membrane varies between species. Another source of variance stems from the shuttle of electrons beyond the mitochondrial membrane. The NADH generated from glycolysis cannot easily enter mitochondria. Thus, electrons are picked upwards on the within of the mitochondria by either NAD⁺ or FAD⁺. Fewer ATP molecules are generated when FAD⁺ acts equally a carrier. NAD⁺ is used as the electron transporter in the liver and FAD⁺ in the encephalon, and so ATP yield depends on the tissue being considered.

Another cistron that affects the yield of ATP molecules generated from glucose is that intermediate compounds in these pathways are used for other purposes. Glucose catabolism connects with the pathways that build or break downwardly all other biochemical compounds in cells, and the result is somewhat messier than the ideal situations described thus far. For case, sugars other than glucose are fed into the glycolytic pathway for energy extraction. Other molecules that would otherwise be used to harvest energy in glycolysis or the citric acid cycle may exist removed to form nucleic acids, amino acids, lipids, or other compounds. Overall, in living systems, these pathways of glucose catabolism extract virtually 34 percentage of the free energy independent in glucose.

Mitochondrial Affliction Medico

What happens when the critical reactions of cellular respiration practise not proceed correctly? Mitochondrial diseases are genetic disorders of metabolism. Mitochondrial disorders can arise from mutations in nuclear or mitochondrial Dna, and they result in the production of less energy than is normal in body cells. Symptoms of mitochondrial diseases tin include musculus weakness, lack of coordination, stroke-like episodes, and loss of vision and hearing. Most affected people are diagnosed in babyhood, although there are some adult-onset diseases. Identifying and treating mitochondrial disorders is a specialized medical field. The educational training for this profession requires a higher education, followed by medical school with a specialization in medical genetics. Medical geneticists tin exist lath certified past the American Board of Medical Genetics and go on to become associated with professional organizations devoted to the study of mitochondrial disease, such as the Mitochondrial Medicine Guild and the Lodge for Inherited Metabolic Disease.

Department Summary

The citric acid wheel is a series of chemical reactions that removes high-energy electrons and uses them in the electron transport chain to generate ATP. One molecule of ATP (or an equivalent) is produced per each turn of the cycle.

The electron transport chain is the portion of aerobic respiration that uses costless oxygen equally the final electron acceptor for electrons removed from the intermediate compounds in glucose catabolism. The electrons are passed through a serial of chemical reactions, with a small corporeality of costless energy used at three points to transport hydrogen ions across the membrane. This contributes to the slope used in chemiosmosis. As the electrons are passed from NADH or FADH₂ down the electron transport chain, they lose energy. The products of the electron ship chain are h2o and ATP. A number of intermediate compounds can be diverted into the anabolism of other biochemical molecules, such as nucleic acids, non-essential amino acids, sugars, and lipids. These same molecules, except nucleic acids, tin serve as energy sources for the glucose pathway.

Glossary

acetyl CoA: the combination of an acetyl group derived from pyruvic acid and coenzyme A which is made from pantothenic acrid (a B-grouping vitamin)

ATP synthase: a membrane-embedded protein circuitous that regenerates ATP from ADP with free energy from protons diffusing through information technology

chemiosmosis: the movement of hydrogen ions downwardly their electrochemical slope across a membrane through ATP synthase to generate ATP

citric acid cycle: a serial of enzyme-catalyzed chemical reactions of fundamental importance in all living cells that harvests the energy in carbon-carbon bonds of saccharide molecules to generate ATP; the citric acid cycle is an aerobic metabolic pathway because it requires oxygen in later on reactions to go along

electron transport chain: a series of four large, multi-protein complexes embedded in the inner mitochondrial membrane that accepts electrons from donor compounds and harvests energy from a serial of chemic reactions to generate a hydrogen ion gradient across the membrane

oxidative phosphorylation: the production of ATP by the transfer of electrons downwardly the electron transport concatenation to create a proton gradient that is used by ATP synthase to add phosphate groups to ADP molecules

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