Figure 3: The cellular metabolic response to hypoxia. Under normal oxygen levels, glucose is converted into pyruvate through the process of glycolysis and then enters the mitochondrion and generates energy (in the form of ATP) through the process of oxidative respiration. Under hypoxic conditions, and in highly proliferating cells, however, pyruvate is converted into lactate which is actively secreted from the cell. In cancer, the reduced activity of the catalytic enzyme pyruvate kinase induces the pentose phosphate pathway which in turn limits ROS accumulation, diminishes oxidative damage and so promotes tumour growth. Adapted by Grüning and Ralser (2011).