Proteinoid

Proteinoid refers to polymers formed by the thermal condensation of amino acids, produced by heating amino acids to promote dehydration reactions. The resulting non-biological polymers are not true proteins, since they lack defined sequences and a genetic blueprint. When these proteinoids are dissolved in water, they can self-assemble into microscale spheres known as proteinoid microspheres.

Proteinoids exhibit a range of physical properties that depend on their composition. They often form hollow, porous, or semi-porous spheres and can encapsulate small molecules. Their aggregates may swell or shrink in response to changes in temperature, pH, or ionic conditions. Some proteinoid compositions display primitive catalytic activity at their surfaces due to functional groups on the amino acid residues, contributing to discussions about early chemical evolution and compartmentalized chemistry.

Historically, proteinoids were central to origin-of-life research in the mid-20th century. American biochemist Sidney W. Fox conducted experiments in the 1950s and 1960s in which proteinoid microspheres were proposed as potential precursors to protocells, capable of incorporating nutrients and exhibiting simple metabolism-like behavior under prebiotic conditions.

Today, proteinoids are viewed mainly as a historical and niche model rather than widely accepted evidence for the origin of life. They illustrate how simple abiotic processes can produce self-assembled, compartmentalized structures, but they lack genetic information, defined sequence, and robust replication. Contemporary protocell research more often emphasizes lipid vesicles, coacervates, or synthetic polymersomes, while proteinoids remain a topic of historical interest in origin-of-life studies.