Question:medium

How many times does oxidation occur in the Krebs cycle of cellular respiration?

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Each oxidation step in the Krebs cycle is coupled with the reduction of an electron carrier (NAD\(^+\) or FAD), which later donates electrons to the electron transport chain to generate ATP.
Updated On: Jan 13, 2026
  • Once
  • Twice
  • Three times
  • Four times
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The Correct Option is D

Solution and Explanation

Step 1: The Krebs cycle, also identified as the citric acid cycle, is a fundamental metabolic pathway within cellular respiration. Located in the mitochondrial matrix, its function is to oxidize acetyl-CoA into carbon dioxide. This process simultaneously reduces NAD\(^+\) and FAD to NADH and FADH\(_2\), respectively, which subsequently fuel ATP production in the electron transport chain.

Step 2: Oxidation reactions within the Krebs cycle occur in these specific steps: 1. Isocitrate undergoes oxidation to form \(\alpha\)-ketoglutarate, reducing NAD\(^+\) to NADH. 2. \(\alpha\)-ketoglutarate is oxidized to succinyl-CoA, also reducing NAD\(^+\) to NADH. 3. Succinate is oxidized to fumarate, reducing FAD to FADH\(_2\). 4. Malate is oxidized to oxaloacetate, with a reduction of NAD\(^+\) to NADH. Consequently, oxidation takes place four times throughout the Krebs cycle.

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