Accumulation of NADH inhibits the Krebs cycle by inhibiting:
Correct answer: D. Pyruvate dehydrogenase
- A. Citrate synthase
- B. Isocitrate dehydrogenase
- C. α-Ketoglutarate dehydrogenase
- D. Pyruvate dehydrogenase
Explanation
Accumulation of NADH inhibits the Krebs cycle primarily by suppressing enzymes involved in oxidative reactions. High levels of NADH indicate that the cell has enough reducing power, signalling a reduced need for further oxidation of metabolites. This leads to inhibition of key enzymes such as pyruvate dehydrogenase, which prevents the conversion of pyruvate into acetyl-CoA and slows the entry of carbon into the Krebs cycle. Within the cycle itself, NADH inhibits isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, both of which are responsible for generating NADH during the oxidation of intermediates. By inhibiting these enzymes, the cycle's rate decreases, preventing overproduction of NADH and maintaining energy balance in the cell.
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Cellular respiration explains how cells release energy from glucose through glycolysis, the link reaction, Krebs cycle and electron transport chain. It includes ATP production, substrate-level and oxidative phosphorylation, aerobic versus anaerobic respiration, and the roles of mitochondria, oxygen and fermentation in energy transfer.
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