The Krebs cycle was founded by Hans Adolf Krebs in 1953, 1 however many of the reaction pathways were discovered earlier by its link to fumaric acid by Albert Szent-Györgyi in 1937.2 The Krebs cycle requires oxygen to function, so it is an integral pathway for all aerobic organisms to generate ATP.
The Krebs cycle (Citric Acid Cycle or TCA cycle) occurs in the mitochondrial matrix. The pyruvates generated from glycolysis are converted to two acetyl-coenzyme As, which each degrade to help form citrate. The cycle is known to be recycling because the reactant of citrate is consumed at the beginning, and regenerated at the end of the cycle. Citrate goes through many chemical reactions aided by enzymes, an example is the production of carbon dioxide by the loss of two carboxyl groups – the residual electrons enter oxidative phosphorylation to produce more ATP.
1The Nobel Prize in Physiology or Medicine 1953. The Nobel Foundation. Retrieved at http://www.nobelprize.org/nobel_prizes/medicine/laureates/1953/
2The Nobel Prize in Physiology or Medicine 1937. The Nobel Foundation. Retrieved at http://www.nobelprize.org/nobel_prizes/medicine/laureates/1937/
3 Nelson, D.L., & Cox, M.M. Lehninger Principles of Biochemistry, 6th Edition.