The chemical process of breaking down glucose is called glycolysis. This process occurs in the cytoplasm of cells, where one molecule of glucose (a six-carbon sugar) is converted into two molecules of pyruvate (three-carbon molecules). Glycolysis occurs in both aerobic and anaerobic conditions and produces a net gain of ATP (adenosine triphosphate) for energy utilization in metabolic processes. It is the first step in cellular respiration, leading to further energy extraction in the presence of oxygen or via fermentation in its absence.