Hans Krebs won the 1953 Nobel Prize in Physiology or Medicine for discovering the citric acid cycle. The cycle is a central sequence of chemical reactions that helps cells extract usable energy from nutrients.
Krebs described the cycle in 1937 while working in Britain. It begins when acetyl-CoA combines with oxaloacetate and proceeds through a repeating series of reactions in which carbon dioxide is released and energy-rich molecules are produced. In aerobic organisms, the cycle takes place mainly in mitochondria.
The pathway is also called the Krebs cycle or the tricarboxylic acid cycle. A common mix-up is confusing it with glycolysis, which is a separate pathway that breaks glucose into smaller molecules before the citric acid cycle uses its products. Krebs shared the prize with Fritz Lipmann, who was honored for discovering coenzyme A and its importance in metabolism.
The cycle is not simply a one-way fuel-burning chain: several of its intermediates also serve as starting materials for biosynthesis.