November 22 marks the passing of Hans Adolf Krebs. Krebs was a German chemist who was awarded the 1953 Nobel Prize in Medicine for the discovery of the citric acid cycle
or the Krebs cycle. The Krebs cycle is a series of chemical reactions that take place in cells where food is broken down into carbon dioxide, water and energy. The reactions take place in the mitochondria of cells as part of the process of cellular respiration. At the beginning of the cycle, an acetyl group broken down from food combines with a four-carbon molecule called oxaloacetate to make a six-carbon compound, citric acid. The citric acid molecule is rearranged and stripped of two of its carbon atoms during the process releasing carbon dioxide and 4 electrons. At the end of the cycle, a molecule of oxaloacetate remains, which can combine with another acetyl group to being the cycle again.
Find out more about Hans Krebs and what else occurred on this day in science history