Chemical Origins of Life

The citric acid (or Krebs) cycle is a core metabolic pathway conserved amongst all aerobic cells. How this pathway came to be in the absence of complex macromolecules (enzymes) in the primordial soup is a key question to the origins of life. Several of the steps of the citric acid cycle involve decarboxylation or oxidation and their reverse reactions provide an interesting platform for creating useful organic molecules from carbon dioxide. A recent paper published in the Journal of the American Chemical Society has driven the reverse reactions of several steps of the TCA cycle using photoreactions and a simple mineral catalyst, ZnS (full text, may require subscription). In total, 3 of the 5 reductive reactions of the reverse Krebs cycle were succesfully driven in this manner, demonstrating the plausibility of the idea that useful biomolecules can be generated in a prebiotic system.