Oxygen is not used at any point in the citric acid cycle. However, the cycle will not work without oxygen because

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To understand why the citric acid cycle cannot run to completion without oxygen, we need to examine the role of oxygen in cellular respiration.
Option 1: 'molecular O2 will regulate many of the enzyme steps.' In reality, the regulation of the cycle is not governed by direct sensing of O2 at enzyme steps within the cycle itself. Regulation occurs through allosteric controls and substrate availability, not primarily by O2 as a direct regulator of those enzymes within the cycle.
Option 2: 'oxygen is necessary to transcribe and translate enzymes for the reactions.' While oxygen demand exists for overall cellular respiration, transcription and translation of enzymes are not the immediate reason the cycle halts without O2. The cycle can proceed enzymatically as long as substrates and cofactors are present; the bottleneck is the availability of NAD+ and FAD, not the direct need to synthesize enzymes.
Option 3: 'oxygen is needed to regenerate electron carriers.' This is the key point. During respiration, NADH and FADH2 produced by the citric acid cycle must be oxidized back to NAD+ and FAD to sustain the cycle. The electron transport chain, which requires oxygen as the final electron acceptor, regenerates these carriers. Without oxygen to accept electrons, NAD+ and FAD are not regenerated efficiently, and the cycle cannot proceed because dehydrogenase reactions in the cycle rely on NAD+ and FAD being available.
Option 4: 'not enough energy is generated without O2 to run the cycle.' It’s true that oxidative phosphorylation yields much of the energy, but the cycle itself can operate independent of ATP yield per se if NAD+ and FADH2 can be reoxidized. The cycle’s progression is limited primarily by the availability of oxidized cofactors, not by a lack of energy per se. Moreover, the statement oversimplifies the mechanism, since the essential issue is cofactor regeneration rather than immediate energy shortfall alone.
In summary, the most accurate explanation is that the citric acid cycle depends on regenerating its electron carriers (NAD+ and FAD) via the electron transport chain, which requires oxygen as the final electron acceptor. Without oxygen, NAD+ and FAD cannot be replenished efficiently, stalling the cycle despite the presence of substrates and enzymes. The other options misstate the regulatory role of O2, the necessity of transcription/translation for immediate cycle operation, or attribute the limitation to energy output alone rather than cofactor regeneration.

Oxygen is not used at any point in the citric acid cycle. However, the cycle will not work without oxygen because

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Oxygen is not used at any point in the citric acid cycle. However, the cycle will not work without oxygen because

View Explanation

Log in for full answers

Similar Questions

Question at position 93 The final electron acceptor in aerobic cellular respiration is:FADH2NADHO2CO2

Question at position 3 Aerobic respiration is the way that we:produce CO2 from O2make ATP from CO2produce O2 from CO2synthesize glucoseget chemical energy from our food

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In aerobic organisms, the ultimate electron acceptor in the _____ of carbon fuels is _____.

One of the following was either used or produced in both pyruvate processing and the citric acid cycle - which one?

Which one of the following does not take place in the mitochondrial matrix?

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