If there are no reactions in the citric acid cycle that use oxygen, O 2 , why does the cycle operate only in aerobic conditions?

OK. Hello everyone. So this question is asking us which statement best explains why the citric acid cycle operates in aerobic conditions. So here we have four different answer options labeled A through D which we'll discuss in greater detail throughout this video. But for now, let's just recall the fact that the phrase aerobic conditions refers to the fact that oxygen is required for the citric acid cycle to operate. And so with this context in mind, let's start with option A which reads that the oxidized co enzymes N ad positive and F ad essential for the citric acid cycle are regenerated through electron transport which needs oxygen. So the question is, is this statement true and the answer is actually yes. And if you recall this is because oxygen behaves as a sort of electron acceptor. So these co enzymes in their reduced form are known as N A DH and fa DH too. Once these carriers have performed their function, these electrons are often transferred to molecular oxygen to which N ad positive and F ad are then regenerated. So they can repeat the process all over again. So statement one is true or statement A moving on now to statement B it says that the citric acid cycle directly consumes oxygen to produce energy rich molecules needed for cellular respiration in mitochondria. So this statement option B is actually incorrect. And the reason for that is because it implies that oxygen is being directly consumed during the citric acid cycle. And this is the part that's misleading because that's the part that's not true, right? The citric acid cycle doesn't directly consume oxygen. Instead, it's the citric acid cycle produces both N A DH and FA H two, these reduced co enzymes. Now, N A DH and FA DH two will require oxygen as mentioned when talking about answer choice. A but the citric acid cycle itself does not directly use oxygen. So that's why statement B is not true. Moving on to statement C it says that the citric acid cycle produces N A DH and FA DH two which require oxygen to be synthesized into a TP directly via electron transport. Now, option C is not correct either because it's implying that N A DH and FA DH two are directly converted into a TP and that's not accurate, right? Because recall that N A DH and FA DH two are essential electron transporters, but they themselves are not converted into any other product. Rather they go back and forth between their oxidized and reduced forms as they are transferring electrons. So just to clarify C is not correct, right? Because our co enzymes are essential for synthesizing A TP, but they themselves are not converted into a TP. This brings us now to option D which says that oxygen is required to convert acetylate into carbon dioxide and water during the citric acid cycle for energy release. Now, in the case of option D, while it is true that acetyl coa is converted into carbon dioxide and water during the citric acid cycle, that process does not directly involve oxygen. So we can't say that it's required for this reaction to take place. Meaning that option D is not correct either. And so that leads us now to our final answer, which is going to be option A in the multiple choice because the oxidized co enzymes N ad positive and F ad essential for the citric acid cycle are regenerated through electron transport, which needs oxygen. So there you have it. And with that being said, thank you so very much for watching. And I hope you found this helpful.

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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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4:45 minutes

Problem 87

Textbook Question

If there are no reactions in the citric acid cycle that use oxygen, O₂, why does the cycle operate only in aerobic conditions?

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 high-energy molecules like NADH and FADH₂, which are later used in the electron transport chain (ETC) to produce ATP.

Recognize the role of oxygen: While the citric acid cycle itself does not directly use oxygen (O₂), the NADH and FADH₂ produced in the cycle are oxidized in the ETC, which requires oxygen as the final electron acceptor.

Connect the dependency: If oxygen is not available, the ETC cannot function. This leads to a buildup of NADH and FADH₂, which are not converted back to their oxidized forms (NAD⁺ and FAD). These oxidized forms are essential for the citric acid cycle to continue operating.

Explain the aerobic condition: Without oxygen, the lack of NAD⁺ and FAD halts the citric acid cycle because these molecules are required to accept electrons during the cycle's reactions.

Summarize the relationship: Although the citric acid cycle does not directly use oxygen, it depends on the availability of NAD⁺ and FAD, which are regenerated in the oxygen-dependent ETC. Therefore, the cycle operates only under aerobic conditions.

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Key Concepts

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

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 energy carriers like NADH and FADH₂. Although it does not directly use oxygen, it is crucial for aerobic respiration, as it provides the reducing agents needed for the electron transport chain.

Aerobic Conditions

Aerobic conditions refer to environments where oxygen is present, allowing organisms to perform cellular respiration efficiently. In these conditions, the electron transport chain can operate, utilizing the NADH and FADH₂ produced in the citric acid cycle to generate ATP through oxidative phosphorylation, which is essential for energy production.

Electron Transport Chain

The electron transport chain (ETC) is a series of protein complexes located in the inner mitochondrial membrane that transfer electrons from NADH and FADH₂ to oxygen, forming water. This process creates a proton gradient that drives ATP synthesis. The citric acid cycle feeds into the ETC, linking its operation to the presence of oxygen, which is why the cycle is primarily active under aerobic conditions.

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