The breakdown of glucose into pyruvate occurs in the cytoplasm of cells. This process is known as glycolysis and represents the initial stage of cellular respiration. During glycolysis, a single molecule of glucose, a six-carbon sugar, is enzymatically broken down into two molecules of pyruvate, each containing three carbon atoms. This process occurs in the cell’s cytoplasm, making it the common starting point for energy extraction from glucose in various organisms, regardless of their oxygen availability. Following glycolysis, the subsequent steps of cellular respiration, such as the Krebs cycle and oxidative phosphorylation, may occur in different cellular compartments.