Which molecule is primarily regenerated during anaerobic respiration?

During anaerobic respiration, the primary molecule that is regenerated is NAD+. This process occurs when glycolysis is taking place, allowing cells to generate ATP without oxygen. In glycolysis, glucose is broken down into pyruvate, resulting in the production of NADH. However, since anaerobic conditions prevent the electron transport chain from functioning, NADH cannot be oxidized back to NAD+ through oxidative phosphorylation.

To ensure that glycolysis can continue and ATP production is maintained, cells must regenerate NAD+ from NADH. This is accomplished through fermentation pathways, where pyruvate is converted into various byproducts, such as lactic acid in lactic acid fermentation or ethanol and carbon dioxide in alcoholic fermentation. The key outcome of these fermentation processes is the conversion of NADH back to NAD+, enabling glycolysis to progress and sustain energy production in the absence of oxygen.

The regeneration of NAD+ is crucial because it ensures that the cellular metabolic processes requiring this coenzyme can continue, enabling the cell to survive under anaerobic conditions.