FIGURE 12-3 The glycolytic pathway. A series of ten reactions degrades glucose to pyruvate. Two reactions consume ATP, forming ADP and phosphorylated sugars (red), two generate ATP from ADP by substrate-level phosphorylation (green), and one yields NADH by reduction of NAD⁺ (yellow). Note that all the intermediates between glucose and pyruvate are phosphorylated compounds. Steps 1, 3 and 10, with single arrows, are essentially irreversible (have large negative ΔG values) under ordinary conditions in cells.