Chloroplasts perform many metabolic reactions in green leaves. In addition to CO₂ fixation—incorporation of gaseous CO₂ into small organic molecules and then sugars—the synthesis of almost all amino acids, all fatty acids and carotenes, all pyrimidines, and probably all purines occurs in chloroplasts. However, the synthesis of sugars from CO₂ is the most extensively studied biosynthetic pathway in plant cells. We first consider the unique pathway, known as the Calvin cycle (after discoverer Melvin Calvin), that fixes CO₂ into three-carbon compounds, powered by energy released during ATP hydrolysis and oxidation of NADPH.