Final answer:
In the final step of the Krebs cycle, NAD+ is reduced to NADH during the oxidation of L-malate to oxaloacetate, completing the cycle and preparing for another round.
Step-by-step explanation:
The final step of the Krebs cycle involves the regeneration of oxaloacetate, which is produced when NAD+ is reduced to NADH. During this process, L-malate (malate) is oxidized to oxaloacetate by the enzyme malate dehydrogenase, and one molecule of NAD+ is converted to NADH + H+. This transformation is crucial as the oxaloacetate acts as the starting point for another turn of the Krebs cycle whenever a new acetyl CoA molecule enters. It also has implications beyond the Krebs cycle, as NADH is a critical energy carrier and its oxidation in later stages of cellular respiration is vital for ATP synthesis.