Cellular and theoretical chimeras: piecing together how cells process energy.

AMONG THE fantastic creatures that Homer described in the Iliad is the chimera, a fire-breathing monster with the head of a lion, the body of a goat and the tail of a serpent. Biologically, the chimera is unimaginable-a quintessentially mythical creature. Yet as an improbable hybrid, it also served as a model for naming another, very real product of cellular biochemistry in the 1970s. Using a dramatic new experimental technique, chemists pieced together parts of cell organelles from different species.’ Though the fragments had been extracted from cells representing three different kingdoms, they functioned together to produce adenosine triphosphate, or ATP, the unit of energy in the cell. The chimeric vesicles were striking-and persuasive, as well. They helped resolve a deep theoretical debate about how cells process energy at the stage of oxidative phosphorylation. The experimentally produced cellular chimeras are thus important landmarks in the history of bioenergetics. They are also relevant to the philosophy of experiment. In this case, they represent a special category of ‘capstone experiments’. The chimeras demonstrated that several domains of experiment could be pieced together (though none of the individual elements was itself novel). The notion of a chimera, or a mosaic of divergent components, also describes how the broader controversy itself was resolved. The episode illustrates that, contrary to many models of scientific change, theories or models may be pieced together into ‘conceptual chimeras’. The image of chimeras thus offers a common theme for several significant conclusions about the history of bioenergetics, the philosophy of experiment, and the dynamics of conceptual change.