Write down the reactions that produce NADH during Krebs cycle.
The Krebs cycle, also called the citric acid cycle, is a central metabolic pathway that generates energy carriers, including NADH, which fuel ATP production in cells. Two key steps in the cycle produce NADH. First, isocitrate is converted into alpha-ketoglutarate by isocitrate dehydrogenase. During this reaction, isocitrate is oxidized, CO₂ is released, and NAD⁺ is reduced to NADH:
Isocitrate + NAD⁺ → alpha-ketoglutarate + CO₂ + NADH + H⁺
Second, alpha-ketoglutarate is transformed into succinyl-CoA via the alpha-ketoglutarate dehydrogenase complex. This step also releases CO₂ and reduces NAD⁺ to NADH:
alpha-ketoglutarate + NAD⁺ + CoA → succinyl-CoA + CO₂ + NADH + H⁺
These NADH molecules then carry high-energy electrons to the electron transport chain, where their energy drives ATP synthesis through oxidative phosphorylation. Because each glucose molecule produces two pyruvate molecules, the Krebs cycle runs twice per glucose, generating four NADH from these two steps alone. This highlights their importance in cellular energy production, powering metabolic processes and sustaining life.
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