Question:
The fate of a cell in which pyruvate dehydrogenase is completely inhibited will be:
The fate of a cell in which pyruvate dehydrogenase is completely inhibited will be:
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Lactate fermentation is crucial not for the energy in lactate itself, but to recycle $\text{NAD}^+$ so that the glycolysis pathway can continue yielding its modest 2 ATP per glucose under anaerobic or blocked conditions.
Updated On: Jun 16, 2026
- Glycolysis continues with $\text{NAD}^+$ regeneration via lactate fermentation, yielding 2 ATP per glucose molecule.
- Pyruvate accumulates and enters the Krebs cycle via an alternative pathway, yielding 32 ATP per glucose molecule.
- Glycolysis stops due to $\text{NAD}^+$ depletion, and no ATP is produced.
- Pyruvate is converted to acetyl CoA, yielding 8 ATP per glucose molecule via fermentation.
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Question:
The question asks about the metabolic consequences of completely inhibiting the enzyme pyruvate dehydrogenase (PDH) in a cell.
Step 2: Detailed Explanation:
• Pyruvate dehydrogenase (PDH) is a key mitochondrial enzyme complex that catalyzes the link reaction.
• This reaction converts pyruvate (produced via glycolysis in the cytoplasm) into acetyl-coenzyme A (acetyl-CoA) in the mitochondrial matrix.
• Acetyl-CoA is the primary input molecule for the tricarboxylic acid (TCA) cycle (Krebs cycle).
• When PDH is completely inhibited, pyruvate cannot be converted into acetyl-CoA, effectively blocking the aerobic respiration pathway.
• As aerobic metabolism halts, the cell must rely solely on anaerobic glycolysis to produce adenosine triphosphate (ATP).
• However, glycolysis requires a continuous supply of oxidized nicotinamide adenine dinucleotide ($\text{NAD}^+$) to convert glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate.
• Under aerobic conditions, $\text{NAD}^+$ is regenerated by the electron transport chain (ETC) in the mitochondria.
• Without PDH and aerobic respiration, the cell must regenerate $\text{NAD}^+$ anaerobically through lactate fermentation, where lactate dehydrogenase reduces pyruvate to lactate while oxidizing NADH back to $\text{NAD}^+$.
• This anaerobic pathway allows glycolysis to continue, producing a net yield of 2 ATP per glucose molecule.
Step 3: Final Answer:
Therefore, glycolysis continues with $\text{NAD}^+$ regeneration via lactate fermentation, yielding 2 ATP per glucose molecule.
The question asks about the metabolic consequences of completely inhibiting the enzyme pyruvate dehydrogenase (PDH) in a cell.
Step 2: Detailed Explanation:
• Pyruvate dehydrogenase (PDH) is a key mitochondrial enzyme complex that catalyzes the link reaction.
• This reaction converts pyruvate (produced via glycolysis in the cytoplasm) into acetyl-coenzyme A (acetyl-CoA) in the mitochondrial matrix.
• Acetyl-CoA is the primary input molecule for the tricarboxylic acid (TCA) cycle (Krebs cycle).
• When PDH is completely inhibited, pyruvate cannot be converted into acetyl-CoA, effectively blocking the aerobic respiration pathway.
• As aerobic metabolism halts, the cell must rely solely on anaerobic glycolysis to produce adenosine triphosphate (ATP).
• However, glycolysis requires a continuous supply of oxidized nicotinamide adenine dinucleotide ($\text{NAD}^+$) to convert glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate.
• Under aerobic conditions, $\text{NAD}^+$ is regenerated by the electron transport chain (ETC) in the mitochondria.
• Without PDH and aerobic respiration, the cell must regenerate $\text{NAD}^+$ anaerobically through lactate fermentation, where lactate dehydrogenase reduces pyruvate to lactate while oxidizing NADH back to $\text{NAD}^+$.
• This anaerobic pathway allows glycolysis to continue, producing a net yield of 2 ATP per glucose molecule.
Step 3: Final Answer:
Therefore, glycolysis continues with $\text{NAD}^+$ regeneration via lactate fermentation, yielding 2 ATP per glucose molecule.
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