On the origin of metabolic pathways

Area of Science:

• Origin of life studies
• Prebiotic chemistry
• Metabolic pathway evolution

Background:

• The heterotrophic theory is the leading hypothesis for the origin of life, supported by experimental evidence of prebiotic synthesis under reducing conditions.
• Autotrophy, where organisms synthesize their own constituents, differs significantly from heterotrophy, which utilizes external organic compounds.
• Existing biosynthetic pathways in the last common ancestor (LCA) diverge from proposed prebiotic synthetic pathways.

Purpose of the Study:

• To propose a semienzymatic theory for the origin of metabolism.
• To bridge the gap between prebiotic chemistry and the metabolic pathways of the last common ancestor (LCA).
• To incorporate environmental prebiotic compounds and compounds from early metabolic pathways into the origin of metabolism.

Main Methods:

• Review of experimental evidence supporting heterotrophic origin of life.
• Comparison of prebiotic synthesis pathways with known biosynthetic pathways.
• Development of a theoretical framework for a semienzymatic origin of metabolism.

Main Results:

• Prebiotic synthesis of organic monomers is feasible under reducing conditions, supporting heterotrophic origins.
• Metabolic pathway evolution likely involved steps closer to prebiotic chemistry than to the LCA's pathways.
• Early metabolism may have utilized transient biosynthetic routes not present in extant organisms.

Conclusions:

• The semienzymatic theory offers a plausible model for the origin of metabolism, integrating prebiotic compounds and leaked pathway intermediates.
• This theory suggests a gradual transition from prebiotic chemistry to early biological metabolism.
• Understanding these early metabolic steps is crucial for comprehending the origin of life.