We talk of burning food in a combustion process, producing CO 2 and H 2 O from food and O 2 . Explain how O 2 is involved in the process although no O 2 is directly involved in the citric acid cycle.

Hi, everybody. And welcome back. Our next question says, why do aerobic organisms need 02 molecular oxygen for survival even though no 02 is directly used during the citric acid cycle. And let's think about this. We recall that our citric acid cycle is that process by which acetyl coa which is the result of glycolysis and pyruvate oxidation. So we've had glucose getting converted pyruvate to acetyl coa that enters our citric acid cycle and produces just a one molecule of A TP or GTP directly. But it reduces a bunch of N AD plus and some F ad which bring those electrons over to the electron transport chain where those electrons allow the creation of proton gradient and protons moving down that gradient power the synthesis of A TP. So you have this big long process with finishing it with this cycle that ends up generating a TP. So with that in mind, let's look at our answer choices and evaluate them. So to a says oxygen 02 is required to initiate the citric acid cycle, but it is not required to initiate the citric acid cycle. It is acetyl coa that enters that cycle that comes from the processing of glucose. So, no, that is not required to initiate that. It is a seal co A that's required to initiate the citric acid cycle. So cross out twice a twice bo two combines with CO2 produced during the citric acid cycle to form a TP. Well, this is definitely not the case. There is carbon dioxide produced during the citric acid cycle since we are losing two carbon atoms that have entered by way of acetyl coa. But that is not what forms a TP. We have one molecule form by substrate level phosphorylation and more a TP generated when electrons that are result of the oxidation of glucose are delivered to the electron transport chain by N A DH fa DH two and through their energy harvested in electron transport chain. A TP is then synthesized. So choice B incorrect. Also choice CO2 serves as an ultimate electron acceptor at the end of the electron transport chain. And this is true. So choice C is our answer. Those electrons go down the electron transport chain losing a little bit of energy each time. And at the very end, they get transferred to 02 where they generate water. But even though the 02 is at the very end of this entire process, the whole thing will shut down without oxygen to accept those electrons. Imagine a brigade of firefighters with buckets of water. If the last firefighter in the chain stops accepting buckets, the whole thing breaks down. So that's why oxygen is essential even though it's not being consumed directly in the citric acid cycle. So we have our answer. But to be thorough, let's just look at choice. Do two aids, the conversion of pyruvate to acetyl coa well, this might stop us for a moment. This is an oxidation reaction but it is not 02 that's involved in that reaction. It is N ad plus that gets reduced in that pyruvate oxidation reaction. So pyruvate is oxidized to acetyl coa but its electrons go to N AD plus which becomes N A DH. So twist d not our answer either. So once again, why do aerobic organisms need 02 for survival even though it's not directly used during the citric acid cycle? And the answer is choice. Co2 serves as an ultimate electronic acceptor at the end of the electron transport chain. See you in the next video.

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21. The Generation of Biochemical Energy

The Citric Acid Cycle

GOB Chemistry

21. The Generation of Biochemical Energy

The Citric Acid Cycle

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Problem 80

Textbook Question

We talk of burning food in a combustion process, producing CO₂ and H₂O from food and O₂. Explain how O₂ is involved in the process although no O₂ is directly involved in the citric acid cycle.

Verified step by step guidance

Understand the context: The citric acid cycle (also known as the Krebs cycle) is a central metabolic pathway that generates energy by oxidizing acetyl-CoA derived from carbohydrates, fats, and proteins. While O₂ is not directly involved in the reactions of the citric acid cycle, it plays a crucial role in the overall process of cellular respiration.

Explain the role of O₂ in cellular respiration: O₂ is the final electron acceptor in the electron transport chain, which is the stage of cellular respiration that follows the citric acid cycle. The electron transport chain is located in the inner mitochondrial membrane and is responsible for producing the majority of ATP (energy) in cells.

Connect the citric acid cycle to the electron transport chain: The citric acid cycle produces reduced coenzymes, specifically NADH and FADH₂, which carry high-energy electrons to the electron transport chain. These electrons are passed through a series of protein complexes, ultimately reducing O₂ to form H₂O.

Highlight the importance of O₂: Without O₂ to act as the final electron acceptor, the electron transport chain would cease to function. This would lead to a buildup of NADH and FADH₂, preventing the citric acid cycle from continuing because it relies on the availability of oxidized forms of these coenzymes (NAD⁺ and FAD).

Summarize the connection: Although O₂ is not directly involved in the chemical reactions of the citric acid cycle, it is essential for maintaining the flow of electrons in the electron transport chain. This ensures the regeneration of NAD⁺ and FAD, which are necessary for the citric acid cycle to proceed and for the cell to produce energy efficiently.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Combustion Process

The combustion process refers to the chemical reaction where a substance, typically organic matter like food, reacts with oxygen (O₂) to produce energy, carbon dioxide (CO₂), and water (H₂O). In biological systems, this process is analogous to cellular respiration, where glucose is oxidized to release energy, highlighting the role of O₂ as a crucial reactant in energy production.

Cellular Respiration

Cellular respiration is a metabolic pathway that converts biochemical energy from nutrients into adenosine triphosphate (ATP), with byproducts of CO₂ and H₂O. It consists of several stages, including glycolysis, the citric acid cycle, and oxidative phosphorylation, where O₂ is essential for the final stage, allowing for the efficient production of ATP through the electron transport chain.

Citric Acid Cycle

The citric acid cycle, also known as the Krebs cycle, is a series of enzymatic reactions that occur in the mitochondria, where acetyl-CoA is oxidized to produce electron carriers (NADH and FADH₂) and CO₂. Although O₂ is not directly involved in this cycle, it is critical for the subsequent oxidative phosphorylation stage, where the electron carriers donate electrons to the electron transport chain, ultimately requiring O₂ to regenerate ATP.

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