Citric-acid cycle Metabolic confusion He thought he was lucky Path of life Commentary

Hans Adolf Krebs metabolism

Citric-acid cycle

• In living cells, citric acid is consumed and
• then regenerated in a cycle of reactions
• that generates energy from the
• food you eat in the form of
• adenosine triphosphate.
• Cellular metabolism
• in animals doesn’t
• just break down
• carbs, fats,
• and proteins,
• but synthesizes
• complex molecules.
• Hans Krebs discovered
• the citric-acid cycle using
• Otto Warburg’s manometer,
• a laboratory device that collects
• waste products from tissue samples.

Metabolic confusion

• Warburg’s manometer measures
• intercellular respiratory gases
• of tissue samples
• subjected to varying conditions.
• Studying cellular
• metabolism, Krebs was confused
• by conflicting results
• until he realized
• animal cells produce energy
• in a cycle of eight reactions
• starting and ending
• with citric acid.

He thought he was lucky

• Having worked as Warburg’s assistant
• at the Kaiser Wilhelm Institute for Biology,
• Krebs was dismissed from his position
• as a medical assistant
• at the University of Freiburg
• because he was a Jew.
• He left Germany in 1933
• with thirty manometers
• and was welcomed by
• Cambridge University and
• the University of Sheffield
• where he became the head
• of the biochemistry department
• and the director of the research unit
• for cell metabolism of the
• Medical Research Council.

Path of life

• The citric-acid cycle is common to all organisms
• that live in an oxygenated environment,
• and is likely to have been one of the earliest
• metabolic pathways supporting life on earth.
• As natural as eating and breathing,
• common to yeast, aerobic bacteria, and animal cells,
• it is more common than yawning, scratching, or blinking,
• even more common than selfishness or stupidity.