What molecule is broken down during glycolysis?

During glycolysis, glucose is the molecule that is broken down. Glycolysis is the initial stage of cellular respiration and occurs in the cytoplasm of the cell. In this process, one molecule of glucose, a six-carbon sugar, is enzymatically cleaved into two molecules of pyruvate, which are three-carbon compounds. This metabolic pathway involves a series of ten enzyme-mediated reactions, and it produces a net gain of two ATP molecules and two NADH molecules, which are crucial for later stages of cellular respiration.

The other options, although they are important in metabolic processes, do not serve as the primary substrate for glycolysis. Fructose can enter glycolysis but is converted into intermediates before being metabolized; lactate is a product formed during anaerobic metabolism rather than a substrate, and acetyl-CoA is produced from pyruvate as a result of glycolysis and plays a key role in the citric acid cycle, not directly in glycolysis itself.