AP BIOLOGY

Detailed explanation-1: -When sufficient oxygen is not present in the muscle cells for further oxidation of pyruvate and NADH produced in glycolysis, NAD+ is regenerated from NADH by reduction of pyruvate to lactate. Lactate is converted to pyruvate by the enzyme lactate dehydrogenase.

Detailed explanation-2: -NAD+ can be regenerated in the cytoplasm from NADH through the conversion of pyruvate to lactate by the lactate dehydrogenase (LDH), thereby maintaining active aerobic glycolysis [5].

Detailed explanation-3: -The anaerobic regeneration of NAD is called fermentation. In animal tissues, fermentation reduces pyruvate to lactate, as NADH transfers electrons to pyruvate. This enzyme-catalyzed reaction occurs whenever the available oxygen has been consumed.

Detailed explanation-4: -The 2 molecules of NADH that are generated during glycolysis are then converted back into NAD+ during anaerobic respiration so that glycolysis can continue.